Jun 14 – 18, 2021
Asia/Seoul timezone

Abstracts - Cosmology

ALLAHVERDI, Rouzbeh University of New Mexico Title: Superheavy Dark Matter from String Theory
Abstract: I argue that generic features of string compactifications, namely a high scale of supersymmetry breaking and one or more epochs of modulus domination, can accommodate superheavy neutralino dark matter with a mass around 10^10−10^11 GeV. Interestingly, this mass range may also explain the recent detection of ultra-high-energy neutrinos by IceCube and ANITA via dark matter decay.
AOKI, Shuntaro Chung-ang University Title: Disentangling mass spectra of multiple fields in cosmological collider
It has been recently claimed that cosmological higher order correlation functions of the primordial curvature perturbations play important roles not only for restricting inflation models, but for exploring a new massive particle (isocurvaton) with mass up to the Hubble scale H. This approach known as the cosmological collider has attracted much attention so far, because the energy scale H is typically much higher than that of terrestrial experiments. In this talk, I discuss effects of multiple scalar fields (scalar isocurvatons) with the Hubble scale masses on the inflationary bispectrum in the squeezed limit, particularly paying attention to the question how to disentangle mass spectra of such fields. A characteristic feature associated with nearly degenerate masses in the oscillating part of the bispectrum is investigated in detail.
ASHOORIOON, Amjad Institute for Research in Fundamental Sciences (IPM) Title: Examining the end of inflation with primordial black hole mass distribution and gravitational waves
We explicitly construct a double field inflationary model, which satisfies the latest PLANCK constraints at the CMB scales and produces the whole dark matter energy density as primordial black holes (PBHs), in the mass range $10^{-17}~M_{\odot}\lesssim M_{{}_{\rm PBH}}\lesssim 10^{-13}~M_{\odot}$. The PBHs can be produced after the end of slow-roll inflation from the bubbles of true vacuum that nucleate during the course of inflation. Obtaining PBHs in this mass range enforces the scale of inflation to be extremely low, $10^{-7}~{\rm GeV}\lesssim H \lesssim 10^{-3} ~{\rm GeV}$, which makes the efforts to observe gravitational waves at the CMB scales futile, although it is high enough to allow for a successful Big Bang Nucleosynthesis (BBN). We will show that the shape of the mass distribution of the PBHs is dependent on how inflation ends and the universe settles from the metastable direction to the true one. End of inflation can also be probed by examining the gravitational waves spectrum. In particular, we show that if exit from the rolling metastable direction to the true vacuum of the potential happens through a first-order phase transition (PT) after the end of slow-roll inflation, it leaves behind a stochastic gravitational wave background (SGWB), which is potentially observable by LISA. We also show that PBHs produced during such a first-order PT from the collision of bubble walls contribute negligibly to the PBH mass spectrum. Examining the mass distribution of PBHs and possible SGWB from the end of inflation, we may be able to gain invaluable information about the end of inflation.
AUFFINGER, Jérémy Institut de physique des deux infinis, Lyon, France Title: Dark matter and dark radiation constraints on light primordial black holes
Primordial black holes (PBHs) lighter than $10^9\,$g are at present mostly unconstrained, because they evaporate before Big Bang Nucleosynthesis (BBN). Hence, they can not represent a fraction of dark matter (DM). However, their evaporation products can leave an imprint on the early universe observables. In this talk, we will decribe how the public code BlackHawk has been adapted to compute the Hawking radiation of light PBHs with the addition of a dark sector particle. Depending on this particle mass, it can result in a contribution to warm DM or dark radiation. The first one is further constrained using structure formation thanks to CLASS and the second one contributes to $\Delta N_\text{eff}$, constrained by BBN and CMB (future) experiments. We conclude by giving the Hawking radiation constraints on light PBHs.
BARRIE, Neil IBS-CTPU Title: Affleck-Dine Leptogenesis from Higgs Inflation
Abstract: We investigate the possibility of simultaneously explaining inflation, the neutrino masses and the
baryon asymmetry through extending the Standard Model by a triplet Higgs. The neutrino masses are generated by the vacuum expectation value of the triplet Higgs, while a combination of the triplet and doublet Higgs' plays the role of the inflaton. Additionally, the dynamics of the triplet, and its inherent lepton number violating interactions, lead to the generation of a lepton asymmetry during inflation. The resultant baryon asymmetry, inflationary predictions and neutrino masses are consistent with current observational and experimental results.
BARROSO BELLIDO, Samuel University of Szczecin Title: Entanglement entropy at critical points in the Multiverse
Recently the entanglement entropy between universes has been calculated, an entropy which somehow describes the quantumness of a homogeneous multiverse. The third quantization formalism of canonical quantum gravity is used here. I will show improvements of the results in a more general scenario, studying what happens at critical points of the evolution of a classical universe. We infer the relation of that entanglement entropy with the Hubble parameter of single universes.
BODAS, Arushi University of Maryland College Park Title: Cosmological collider physics beyond the Hubble scale
Abstract: Non-gaussianity in the primordial density fluctuations is an effective probe of new physics during the inflationary era. On-shell production of heavy particles during inflation may leave a distinctive non-analytic signature in the bispectrum, presenting a unique opportunity for the “direct detection” of particles with masses as large as the inflationary Hubble scale (H). However, the strength of this non-analytic signal ordinarily drops exponentially by a Boltzmann-like factor as masses exceed H. I will discuss a mechanism for massive complex scalar fields that gives orders of magnitude larger signal through a derivative coupling of inflaton to the complex scalar current. The operator has a chemical potential-like form, which harnesses the large kinetic energy scale of the inflation (~ 60H) for efficient particle production. I will show that the bispectrum with fNL ∼ O(0.01−10) can be obtained for an extended range of scalar masses (up to ~ 60H), and delineate a procedure to infer the mass of the heavy field and chemical potential scale from the signal.
The talk will be based on the work: arXiv:2010.04727
CYR-RACINE, Francis-Yan University of New Mexico Title: A cosmological dark matter collider experiment
Observations of dark matter structure at the smallest scales can tell us about physical processes taking place in the dark sector at very early times. Here, we point out that the presence of light degrees of freedom coupling to dark matter in the early Universe introduces a localized feature in the halo mass function. This leads to a mass function that is distinct in shape than either warm dark matter or cold dark matter, hence distinguishing these models from other leading classes of dark matter theories. We present analytical calculations of these mass functions and show that they closely match N-body simulations results. We also discuss the impact of these mass functions at high-redshift on the 21-cm signal from cosmic dawn. We briefly discuss how current constraints on the abundance of small-scale dark matter structure do not directly apply to these models due to the multi-scale nature of their mass function.
EBRAHIMIAN, Ehsan Sharif University Title: Dynamical Tidal Locking Theory: A new source of the Spin of Dark Matter Halos
We revisit the question of what mechanism is responsible for the spins of halos of dark matter. The answer to this question is of high importance for modeling galaxy intrinsic alignment, which can potentially contaminate current and future lensing data. In particular, we show that when the dark matter halos pass nearly by each other in dense environments-- namely halo assemblies-- they swing and spin each other via exerting mutual tidal torques. We show that this has a significant contribution to the spin of dark matter halos comparable to that of calculated by the so-called tidal torque theory (TTT). We use the results of state-of-the-art simulation of Illutris to check the prediction of this theory against the simulation data.
ERFANI, Encieh IASBS Title: Primordial Black Holes in the Excursion Set Theory
We study primordial black holes (PBHs) formation in the excursion set theory (EST) in a vast range of PBHs masses with and without confirmed constraints on their abundance. In this work, a new concept of the first touch in the EST is introduced for PBHs formation which takes into account the earlier horizon reentry of smaller masses. Our study shows that in the EST, it is possible to produce PBHs in different mass ranges which could make up all dark matter. We also show that in a broad blue-tilted power spectrum, the production of PBHs is dominated by a smaller mass. Our analysis put an upper limit ~ 0.1 on the amplitude of the curvature power spectrum at length scales relevant for PBHs formation.
ERÖNCEL, Cem DESY Title: Fragmentation of the axion field in the early universe
Abstract: Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it has been subject to extensive theoretical and experimental research in recent years. The most popular ALP production mechanism studied in the literature is the misalignment mechanism, where the ALP field has negligible kinetic energy initially, and it starts oscillating when its mass becomes comparable to the Hubble scale. In most of these studies, the ALP field has been assumed to be a homogeneous classical field, and its quantum fluctuations have been ignored. However a non-zero initial velocity can cause exponential growth in the amplitude of fluctuations, and most of the energy density in the homogeneous mode can be converted to axion particles, known as fragmentation. In this talk, I will present a semi-analytical study of this process, and describe the necessary ingredients for an efficient fragmentation. I will also mention the implications for axion miniclusters.
FUJIKURA, Kohei The University of Tokyo Title: Electroweak-like Baryogenesis with New Chiral Matter
We propose a framework where a phase transition associated with a gauge symmetry breaking that occurs (not far) above the electroweak scale sets a stage for baryogenesis similar to the electroweak baryogenesis in the Standard Model. New chiral fermions charged under the extended gauge symmetry have nonzero lepton numbers, which makes the B-L symmetry anomalous. The new lepton sector contains a large flavor-dependent CP violation, similar to the Cabibbo-Kobayashi-Maskawa phase, without inducing sizable electric dipole moments of the Standard Model particles. A bubble wall dynamics associated with the first-order phase transition and sphaleron processes generate a lepton asymmetry, which is transferred into a baryon asymmetry via the ordinary electroweak sphaleron process. Unlike the Standard Model electroweak baryogenesis, the new phase transition can be of the strong first order and the new CP violation is not significantly suppressed by Yukawa couplings, so that the observed asymmetry can be produced. The model can be probed by collider searches for new particles and the observation of gravitational waves. This seminar is based on arXiv:2103.05005.
GARCIA, Marcos IFT UAM-CSIC Title: Dark Matter Production During Reheating (by example)
I will present a systematic analysis of dark matter production during post-inflationary reheating. The damped oscillations of the inflaton as it decays, the inflaton dissipation rate, the thermalization rate of its decay products, and the evolution of the temperature of the subsequently thermalized radiation are dependent on the shape of the inflaton potential, and they determine the production rate of dark matter. In the context of a non-supersymmetric spin-3/2 dark matter candidate, I will also discuss how to exploit dark matter as a probe of the dynamics during reheating, through smoking-gun signals such as monochromatic neutrinos or gamma-rays, or through power spectrum data (Lyman-alpha forest).
GOUTTENOIRE, Yann Tel Aviv University Title: String Fragmentation in Supercooled Confinement and implications for Dark Matter
A strongly-coupled sector can feature a supercooled confinement transition in the early universe. When fundamental quanta of the strong sector are swept into expanding bubbles of the confined phase, the distance between them is large compared to the confinement scale. The flux linking the fundamental quanta then deforms and stretches towards the wall, producing an enhanced number of composite states upon string fragmentation. The composite states are highly boosted in the plasma frame, which leads to additional particle production through the subsequent deep inelastic scattering. I will discuss the modelling of these dynamics and introduce the consequences for the abundance and energetics of particles in the universe and for bubble-wall Lorentz factors. As a case of study, I will show that the composite dark matter relic density is affected by many orders of magnitude.
GUERRERO MENKARA, Adriana Chung Ang University Title: Cosmology of Linear Higgs-Sigma Models with Conformal Invariance
We consider general linear Higgs-sigma models as ultra-violet completions of the Higgs inflation. We introduce general higher curvature terms beyond Einstein gravity and recast them into a class of linear Higgs-sigma models in the scalar-dual formulation where conformal symmetry is manifest. Integrating out the sigma field in this class of linear sigma models, we obtain the same Higgs inflation Lagrangian of non-linear sigma model type in the effective theory. We show that the successful inflation for sigma field singles out the sigma-field potential derived from the R^2 term and the tracker solution for dark energy at late times can be realized for the R^(p+1) term with −1<p<0. We also discuss the implications of Higgs-sigma interactions for the inflation and the vacuum stability in the Standard Model.
HAYASHI, Takumi University of Tokyo Title: Vacuum decay in de-Sitter spacetime with the Lorentzian path integral
Abstract: False vacuum decay is an important phenomenon in both the quantum field theory and cosmology, and it has been formulated in the Euclidean path integral. However, the Euclidean formalism is not well justified with the dynamical gravity, so it is necessary to explore alternative ways to formulate the false vacuum decay.
Recently, a new method addressing oscillatory behavior of the Lorentzian path integral by saddle-point method is developed and applied to the problem of quantum cosmology, which could clarify the issues in the Euclidean path integral in the false vacuum decay process.
In this talk, I will introduce our novel method to evaluate the decay rate of a false vacuum in the Lorentzian path integral. Although our computation is still limited to cases where gravity is background, we find that the Lorentzian formalism predicts a consistent bubble size and bubble nucleation probability with the ones obtained by the Euclidean formalism. Intriguingly, our computation can be extended to the nucleation of a smaller or larger vacuum bubble as well. This result suggest that the Lorentzian path integral provides a new formalism reliably dealing with the vacuum decay, which could be applicable to the case involving dynamical gravity.
HE, Minxi RESCEU, UTokyo Title: Reheating in the mixed Higgs-R^2 inflation model
The reheating process in the mixed Higgs-R^2 model will be introduced. The mixed Higgs-R^2 model is an observationally favored two-field inflationary model that can serve as the UV extension of the Higgs inflation up to Planck scale free from strongly-coupled issue during inflation and reheating. The inflation dynamics in this model is described by effective R^2 inflation, while the (p)reheating process involves different dominant mechanisms for different parameters, resulting in different reheating temperatures. The Universe can be reheated through tachyonic instability of Higgs which can complete the reheating instantaneously, or through perturbative inflaton decay which leads to much longer reheating and lower reheating temperature.
HERTZBERG, Mark Tufts University Title: The causal structure of superfluid dark matter
Abstract: There has been much interest in novel models of dark matter that exhibit interesting behavior on galactic scales. A primary motivation is the observed Baryonic Tully-Fisher Relation in which the mass of galaxies increases as the quartic power of rotation speed. This scaling is not obviously accounted for by standard cold dark matter. This has prompted the development of dark matter models that exhibit some form of MONDian phenomenology to account for this galactic scaling, while also recovering the success of cold dark matter on large scales. A beautiful example of this are the so-called superfluid dark matter models, in which a complex bosonic field undergoes spontaneous symmetry breaking on galactic scales, entering a superfluid phase with a 3/2 kinetic scaling in the low energy effective theory, that mediates a long-ranged MONDian force. In this work we examine the causality and locality properties of these and other related models
JAHANI POSHTEH, Mohammad Bagher Institute for Research in Fundamental Sciences (IPM) Title: Gravitational lensing by slowly accelerating black holes
Accelerating black holes can be pair produced on cosmic strings, in a de Sitter background, and/or in a background magnetic field. We propose a method to observe the accelerating black holes through the gravitational lensing of these black holes. We show that, for slowly accelerating black holes, the angular position of images in the gravitational lensing effects do not change significantly. However, the differential time delays associated with the images are different with respect to the case of non-accelerating black holes. This is in contrast with when the theory governing the strong gravitational field around the black hole is different from general relativity, where not only the differential time delays but the angular position of images would be different. We conclude that, if the observed angular position of images are compatible with the prediction of general relativity, a possible deviation in the differential time delays between the observed values and those predicted by general relativity, could be due to the acceleration of the black hole.
JINNO, Ryusuke DESY Title: Deformation of the gravitational wave spectrum by density perturbations
Abstract: In recent years, the possibility of having large density perturbations at high wavenumbers has been actively studied, especially in the study of primordial black holes (PBHs). In this presentation, I point out that such density perturbations affect any pre-existing gravitational wave (GW) spectrum through CMB-like effects. Since GWs produced in the early universe propagate through the density perturbations before reaching the observer, GWs coming from each direction experience different evolution depending on the density perturbations. As a result, the observed (directionally averaged) GWs generally have a deformed spectrum compared to the original one. Therefore, by carefully comparing the observed spectrum with the theoretical GW spectrum at the time of production, we may be able to indirectly observe density perturbations at high wevenumbers. In this presentation, I explain how this effect shows up and estimate the maximum expected impact on the GW spectrum, taking into account the latest bound on density perturbations from PBH searches.
JYOTI DAS, Suruj Indian Institute of Technology, Guwahati Title: Low scale leptogenesis and dark matter in the presence of primordial black holes.
Abstract : We study the possibility of low scale leptogenesis along with dark matter (DM) in the presence of primordial black holes (PBH). For a common setup to study both leptogenesis and DM we consider the minimal scotogenic model which also explains light neutrino mass at radiative level. While PBH in the mass range of $0.1-10^5$ g can, in principle, affect leptogenesis, the required initial PBH fraction usually leads to overproduction of scalar doublet DM whose thermal freeze-out occurs before PBH evaporation. PBH can lead to non-thermal source of leptogenesis as well as dilution of thermally generated lepton asymmetry via entropy injection, with the latter being dominant. The parameter space of scotogenic model which lead to overproduction of baryon or lepton asymmetry in standard cosmology can be made consistent in the presence of PBH with appropriate initial mass and energy fraction. On the other hand, for such PBH parameters, the scalar DM is constrained to be in light mass regime where its freeze-out occurs after PBH evaporation. We then discuss the possibility of fermion singlet DM with $N_2$ leptogenesis in the same model where due to singlet nature of DM, its connection with PBH parameters and hence leptogenesis becomes stronger compared to the previous case.
KAMADA, Kohei Research Center for the Early Universe, University of Tokyo Title: Wash-in Leptogenesis as a New Framework for Baryogenesis
Washout of B+L asymmetry by the electroweak sphaleron is an obstacle for a class of baryogenesis such as SU(5) GUT baryogenesis. However, the sphaleron washout works only at a low temperature lower than 100 TeV because at higher temperature we have some approximate conserved charges that prevents from the washout being completed. Thus if we have some other mechanisms after B+L generation before the washout completion, there opens a possibility to avoid the sphaleron washout. In this talk, I present a new idea to implement the mechanism to avoid the sphaleron washout based on the standard type-I seesaw model, which we dub wash-in leptogenesis. With nonvanishing initial chemical potentials for the approximate conserved charges and right-handed neutrinos, they are reprocessed to generate a nonvanishing B-L asymmetry at low temperatures. This mechanism successfully operates at right-handed-neutrino masses as low as a few 100 TeV. This mechanism does not require any $CP$ violation in the neutrino sector and can be implemented even in the regime of strong washout. As concrete examples, I discuss wash-in leptogenesis after axion inflation and in the context of grand unification.
KEELEY, Ryan Korea Astronomy Space Science Institute Title: Testing LCDM with eBOSS / SDSS
In this talk I will review recent progress that the SDSS-IV / eBOSS collaboration has made in constraining cosmology from the clustering of galaxies, quasars and the Lyman-alpha forest. The SDSS-IV / eBOSS collaboration has measured the baryon acoustic oscillation (BAO) and redshift space distortion (RSD) features in the correlation function in redshift bins from z~0.15 to z~2.33. These features constitute measurements of angular diameter distances, Hubble distances, and growth rate measurements. A number of consistency tests have been performed between the BAO and RSD datasets and additional cosmological datasets such as the Planck cosmic microwave background constraints, the Pantheon Type Ia supernova compilation, and the weak lensing results from the Dark Energy Survey. Taken together, these joint constraints all point to a broad consistency with the standard model of cosmology LCDM + GR, though they remain in tension with local measurements of the Hubble parameter.
KOO, Hanwool KASI/UST Title: Cosmology with Type Ia supernovae: Searching for systematics and model independent reconstructions
We analyze the Joint Light-curve Analysis (JLA) Type Ia supernovae (SN Ia) compilation implementing the non-parametric iterative smoothing method. We explore the SN Ia light-curve hyperparameter space and find no dark energy model dependence nor redshift evolution of the hyperparameters. We also analyze the more recent Pantheon SN Ia compilation to search for possible deviations from the expectations of the concordance ΛCDM model. We demonstrate that the redshift binned best fit parameter values oscillate about their full dataset best fit values with considerably large amplitudes. At the redshifts below z≈0.5, we show that such oscillations can only occur in 4 to 5% of the simulations. This might be a hint for some behavior beyond the predictions of the concordance model or a possible additional systematic in the data. In addition, we develop a non-parametric approach using the distribution of likelihoods from the iterative smoothing method. It determines consistency of a model and the data without comparison with another model. Simulating future WFIRST-like data, we show how confidently we can distinguish different dark energy models using this approach.
KRAJEWSKI, Tomasz University of Warsaw Title: Stability of domain walls in generic models.
We study the evolution of cosmological domain walls in models with asymmetric potentials. Our research goes beyond the standard case of spontaneous breaking of an approximate symmetry. The time after which the network will decay depends on the difference of values of the potential in minima, its asymmetry around the maximum separating minima and the bias of initial distribution. Using numerical lattice simulations we determine relative importance of these factors on decay time of networks for generic potentials. We find that even very small departures from the symmetric case lead to rapid decay of the domain wall network. As a result creation of a long lasting network capable of producing observable gravitational wave signals is much more difficult than previously thought.
KUME, Jun'ya RESCEU, University of Tokyo Title: Chiral gravitational effect in primordial thermal plasma
Abstract:Parity violating effects related to quantum anomalies have been discussed in various fields of physics, including cosmology. For example, chiral magnetic effect (CME) is extensively studied since it causes chiral plasma instability which can be ascribed as the possible origin of the primordial magnetic fields. In this talk, I present gravitational counterpart of CME, which is caused by the chiral gravitational anomaly. Since the anomaly connects the left-right asymmetry of the fermions with the helicity of the gravitational waves, there is non-trivial interplay between the primordial gravitational waves and the primordial chiral plasma due to this effect. While comparing it with CME, I will discuss cosmological implications and potential effects on the gravitational wave observation.
LEEDOM, Jacob UC Berkeley Title: Cosmological Tension of Ultralight Axion Dark Matter and its Solutions
Abstract: A number of proposed and ongoing experiments search for axion dark matter with a mass nearing the limit set by small scale structure [O(10-21  eV)]. We consider the late universe cosmology of these models, showing that requiring the axion to have a matter-power spectrum that matches that of cold dark matter constrains the magnitude of the axion couplings to the visible sector. Comparing these limits to current and future experimental efforts, we find that many searches require axions with an abnormally large coupling to Standard Model fields, independently of how the axion was populated in the early Universe. We survey mechanisms that can alleviate the bounds, namely, the introduction of large charges, various forms of kinetic mixing, a clockwork structure, and imposing a discrete symmetry. We provide an explicit model for each case and explore their phenomenology and viability to produce detectable ultralight axion dark matter.
LENOCI, Alessandro DESY Title: Lower Mass Bounds on Fimp Dark Matter
Feebly Interacting Massive Particles (FIMPs) are dark matter candidates that never thermalize in the early universe and whose production takes place via decays and/or scatterings of thermal bath particles. If FIMPs interactions with the thermal bath are renormalizable, a scenario which is known as freeze-in, production is most efficient at temperatures around the mass of the bath particles and insensitive to unknown physics at high temperatures. Working in a model-independent fashion, we consider three different production mechanisms: two-body decays, three-body decays, and binary collisions. We compute the FIMP phase space distribution and matter power spectrum, and we investigate the suppression of cosmological structures at small scales. Our results are lower bounds on the FIMP mass. Finally, we study how to relax these constraints in scenarios where FIMPs provide a sub-dominant dark matter component.
LI, Lingfeng HKUST Title: The Hubble Constant in the Axi-Higgs Univers
Abstract: The $\Lambda$CDM model provides an excellent fit to the CMB data. However, a statistically significant tension emerges when its determination of the Hubble constant $H_0$ is compared to the local distance-redshift measurements. The axi-Higgs model, which couples ultralight axions to the Higgs field, offers a specific variation of the $\Lambda$CDM model. It relaxes the $H_0$ tension as well as explains the $^7$Li puzzle in Big-Bang nucleosynthesis, the $S_8$ tension with the weak-lensing data, and the observed isotropic cosmic birefringence in CMB. In this letter, we demonstrate how the $H_0$ and $S_8$ tensions can be resolved simultaneously, by correlating the axion impacts on the early and late universe. In a benchmark scenario selected for experimental tests soon, the analysis combining the CMB+BAO+WL+SN data yields $H_0 = 71.1 \pm 1.1$~km/s/Mpc and $S_8 = 0.766 \pm 0.011$. Combining this (excluding the SN(supernovae) part) with the local distance-redshift measurements yields $H_0 = 72.3 \pm 0.7$~km/s/Mpc, while $S_8$ is unchanged.
LU, Qianshu Harvard University Title: Spillway Preheating: an efficient particle production mechanism
Abstract: In traditional models of preheating, only an order one fraction of energy is transferred from the inflaton to radiation through nonperturbative resonance production immediately after inflation, due to backreaction effects. We propose a particle production mechanism, "spillway preheating", that could improve the depletion of the inflaton energy density by up to four orders of magnitude. The improvement comes from the fast perturbative decays of resonantly produced daughter particles. They act as a "spillway" to drain these daughter particles, reducing their backreaction on the inflaton and keeping the resonant production effective for a longer period. We also show that the fraction of energy density remaining in the inflaton has a simple inverse power-law scaling in the scenario.
MALEKNEJAD, Azadeh CERN Title: Is Our Universe the Remnant of Chiral Anomaly in Inflation?
Modern cosmology has been remarkably successful in describing the universe from a second after the Big Bang until today. However, its physics before that time is still much less certain. It profoundly involves particle theory beyond the Standard Model to explain long-standing puzzles: the origin of the observed matter asymmetry, and massive neutrinos, as well as the particle physics of dark matter and cosmic inflation. In this talk, I will explain that a new framework based on embedding axion-inflation in left-right symmetric gauge extensions of the SM can possibly solve and relate these seemingly unrelated mysteries of modern cosmology. The baryon asymmetry and dark matter today may be remnants of a pure quantum effect (chiral anomaly) in inflation which is the source of CP violation in inflation. As a smoking
gun, this setup has robust observable signatures for the GW background to be probed by future CMB missions and laser interferometer detectors.
MANTZIRIS, Andreas Imperial College London Title: Cosmological implications of electroweak vacuum instability: constraints on the Higgs-curvature coupling from inflation
Abstract: The current experimentally measured parameters of the Standard Model (SM) suggest that our Universe lies in a metastable electroweak vacuum, where the Higgs field is prone to vacuum decay to a lower state with catastrophic consequences. Our measurements dictate that such an event has not taken place yet, despite the many different mechanisms that could have triggered it in our past light-cone. The focus of our work has been to calculate the probability of the false vacuum to decay during the period of inflation and use it to constrain the last unknown renormalisable SM parameter $\xi$, which couples the Higgs field with space-time curvature. More specifically, we derived lower $\xi$-bounds from vacuum stability in three inflationary models: quadratic and quartic chaotic inflation, and Starobinsky-like power-law inflation. We also took the time-dependence of the Hubble rate into account both in the geometry of our past light-cone and in the Higgs effective potential, which is approximated with three-loop renormalisation group improvement supplemented with one-loop curvature corrections.
MISHRA, Swagat Saurav Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune Title: Curing inflationary degeneracies using reheating predictions and relic gravitational waves
It is well known that the inflationary scenario often displays different sets of degeneracies in its predictions for CMB observables, such as the scalar spectral index $n_{_S}$ and the tensor-to-scalar ratio $r$, making it difficult for CMB observations alone to constitute a unique probe of inflationary cosmology. We demonstrate that by taking into account constraints on the post-inflationary reheating parameters such as the duration of reheating $N_{_{\rm re}}$, its temperature $T_{_{\rm re}}$ and especially its equation of state (EOS), $w_{_{\rm re}}$, it is possible to break this degeneracy in certain classes of inflationary models where identical values of $\lbrace n_{_S}, r \rbrace$ can correspond to different reheating $w_{_{\rm re}}$. The relic gravitational wave (GW) spectrum provides us with another tool to break inflationary degeneracies. This is because the GW spectrum is sensitive to the post-inflationary EOS of the universe. Indeed a stiff EOS during reheating $(w_{_{\rm re}} > 1/3)$ gives rise to a small scale blue tilt in the spectral index $n_{_{\rm GW}} = \frac{d\log{\Omega_{_{\rm GW}}}}{d\log{k}} > 0$, while a soft EOS $(w_{_{\rm re}} < 1/3)$ results in a red tilt. Relic GWs therefore provide us with valuable information about the post-inflationary epoch, and their spectrum can be used to cure inflationary degeneracies in $\lbrace n_{_S}, r\rbrace$.
NOTARI, Alessio Universitat de Barcelona Title: Cosmic Axion Background: the QCD axion as a hot relic
QCD Axions can be produced in various ways in the Early Universe by scatterings and decays from Standard Model particles, forming thus a Cosmic Axion Background that contributes to the abundance of relativistic relics (N_eff). We review in various setups how this is already constrained by present experiments and how it could be observed by future CMB experiments, in particular focusing on the coupling to quarks and leptons, the bounds on the DFSZ model, and also the connection with the Xenon1T excess.
Ó COLGÁIN, Eoin Sogang University Title: A potential Dark Energy narrative
Abstract: As I will show, Hubble tension, if true, sinks the simplest EFT beyond Lambda, i.e. Quintessence, and maybe also Lambda. It is tempting to interpret this as an indication that Dark Energy EFTs are not the right direction. I will attempt to argue that determinations of H0 ~ 73 km/s/Mpc likely fall outside the FLRW paradigm. If true, then this would demystify 70% of the dark Universe.
OKANO, So Tokyo Institute of Technology Title: When does the Schwinger Preheating occur
If the inflaton has a kinetic coupling to U(1) gauge fields, the electric fields are amplified during inflation and then produce charged particles via the Schwinger effect. Using the kinetic approach to the Boltzmann equation, we investigate the dynamics of the charged particle and its back reaction. The produced charged particles temporarily dominate the universe at the end of the inflation in some models, which is called the Schwinger preheating. We found the analytic condition for the Schwinger preheating, using a general attractor solution of the electric fields. In our talk, we will show that our condition explains the numerical results, and discuss influences of the anisotropic background on the dynamics.
PARIKH, Aditya Harvard University Title: Exploring the Co-SIMP Dark Sector.
Abstract: A particularly salient aspect of particle dark matter models is the connection between thermal interactions and cosmological abundance. Extending from the famous WIMP paradigm is a rich sector of dark sector models with different number changing mechanisms, all of which realize a relic abundance via interactions with the Standard Model or itself. In this talk I will introduce one of these scenarios: Co-SIMP dark matter, whose key interactions involve both cannibalistic interactions and couplings to the Standard Model. I will discuss the phenomenology and UV completions of this scenario, as well as constraints and prospects for detection.
ROMPINEVE, Fabrizio Tufts University Title: A Dark Sector to Restore Cosmological Concordance
Observations of the early Universe indicate a Universe expanding today at a (Hubble) rate which is significantly slower than what is measured locally via supernovae, if the ΛCDM model is assumed. Furthermore, the amplitude of matter fluctuations at late times measured by cosmic shear surveys is smaller than what is inferred from the same early Universe observations, assuming the ΛCDM model.
Barring unaccounted systematics, these may be the first hints of new components beyond the ΛCDM model.
In this talk, we present a new phenomenological Dark Sector (DS) model that addresses the tensions above. The scenario features a decaying dark energy fluid which raises the value of H_0 and an ultra-light axion, which suppresses the matter power spectrum. We present results of Monte Carlo Markov Chain searches of the parameter space of this DS model with several early and late Universe datasets. Furthermore, we discuss a possible particle physics realization of this model, with a dark confining gauge sector and its associated axion, highlighting its challenges.
ROSTAMI, Abasalt Institute For Research In Fundamental Sciences(IPM) Title: EFT Compatible PBHs: an Effective Spawning of the Seeds for Primordial Black Holes during Inflation
Most of the inflationary scenarios that try to explain the origin of Primordial Black Holes (PBHs) from the enhancements of the power spectrum to values of order one at the relevant scales, run into clashes with the Effective Field Theory (EFT) criteria or fail to enhance the power spectrum to such large amplitudes. In this paper, we unravel a mechanism of enhancing the power spectrum during inflation without flattening the potential or reducing the sound speed of scalar perturbations. The mechanism is based on this observation in the formalism of Extended EFT of inflation (EEFToI) with the sixth order polynomial dispersion relation for scalar perturbations, that if the quartic coefficient in the dispersion relation is negative and smaller than a certain threshold, the amplitude of power spectrum can be enhanced substantially. The instability mechanism needs to be arranged to kick in at the scales of interest which is related to the mass of the PBHs one would like to produce, which can be ten(s) of solar mass PBHs, suitable for LIGO events, or 10−13−10−17 solar mass PBHs, which can comprise the whole dark matter energy density. This can be accommodated within the EEFToI by endowing time-dependence to the coefficients of the dispersion relation, or in turn, to the couplings in the unitary gauge action. We argue that for the range of parameters that the mechanisms enhance the power spectrum to the required amount, the strong coupling is avoided.
SARMAH, Priyanka IIT bombay Title: Broadband 21 cm cosmological signal from dark matter spin-flip interactions
21 cm cosmology has opened up room to look for new physics interaction and the recent observation of an anomalous absorption dip in the 21 cm global signal by the EDGES experiment has broached a lot of interest from particle physicists. In the light of this, we propose a novel mechanism of dark matter induced spin-flip interactions with electrons through a light axial-vector mediator and show that such a trigger could directly induce a 21 cm absorption signal which is characteristically different from the Standard model of cosmology as well as the excess gas cooling models. We find generically, that our model predicts a strong, broadband absorption signal extending from frequencies as low as 1.4 MHz (z ∼ 1000), from early in the cosmic dark ages where no conventional signal is expected, all the way up to 90 MHz, depending upon the epoch of star formation and X-ray heating. We find a rich set of spectral features that could be probed in current and future experiments looking for the global 21 cm signal. Large portion of our model parameter space of interest are safe from existing particle physics constraints, however future searches for short range spin-dependent forces between electrons on the millimeter to nanometer scale have the potential to discover the light mediator responsible for our predicted signal.
SHAH, Neil Tufts University Title: Real Time Approach to Vacuum Tunneling
Abstract: Recently there has been increasing interest in alternate methods to compute quantum tunneling in field theory. Of particular interest is a stochastic approach which involves (i) sampling from the free theory Gaussian approximation to the Wigner distribution in order to obtain stochastic initial conditions for the field and momentum conjugate, then (ii) evolving under the classical field equations of motion, which leads to random bubble formation. Previous work showed parametric agreement between the logarithm of the tunneling rate in this stochastic approach and the usual instanton approximation. However, recent work claimed excellent agreement between these methods. Here we show that this approach does not in fact match precisely; the stochastic method tends to overpredict the instanton tunneling rate. We numerically implement the stochastic approach to obtain the bubble formation rate for a range of potentials in 1+1-dimensions and find the stochastic method fails to match the instanton. We find that a mismatch in predictions also occurs when sampling from other Wigner distributions, and in single particle quantum mechanics even when the initial quantum system is prepared in an exact Gaussian state. If the goal is to obtain agreement between the two methods, our results show that the stochastic approach would be useful if a prescription to specify optimal fudge factors for fluctuations can be developed.
SHEIKH-JABBARI, Shahin IPM, Tehran Title: Running Hubble Tension
Abstract: Hubble tension is routinely presented as a mismatch between the Hubble constant H_0 determined locally and a value inferred from the flat LCDM cosmology. In essence, the tension boils down to a disagreement between two numbers. Here, assuming the tension is cosmological in origin, we predict that within flat LCDM there should be other inferred values of H_0, and that a "running of H_0 with redshift" can be expected. These additional determinations of H_0 may be traced to a difference between the effective equation of state (EoS) of the Universe and the current standard model. We introduce a diagnostic that flags such a running of H_0.
SIMAKACHORN, Peera Universität Hamburg and DESY Title: "Primordial gravitational waves revealed by a spinning axion"
A fast-spinning axion can dominate the Universe at early times and generates the so-called kination era. The presence of kination imprints a smoking-gun spectral enhancement in the primordial gravitational-wave (GW) background. Current and future-planned GW observatories could constrain particle theories that generate the kination phase. Surprisingly, the viable parameter space allows for a kination era at the PeV-EeV scale and generates a peaked spectrum of GW from either cosmic strings or primordial inflation, which lies inside ET and CE windows.
(Keyword: Cosmology)
SOERENSEN, Philip DESY / Uni Hamburg Title: Axion Dark Matter from Fragmentation
Fragmentation of the axion field may produce the observed DM abundance, which makes it possible for ALP DM to appear with lower values of the axion decay constant than those allowed by the conventional misalignment mechanism. Previously, kinetic misalignment has been proposed to open up this parameter space. We find that for a large range of parameters the field becomes fragmented before kinetic misalignment can take place. Additionally, we demonstrate how the initial velocity necessary for fragmentation can be delivered and study how the process may be constrained or tested via cosmological observables such as BBN and structure formation.
SUZUKI, Motoo T.D.Lee Institute Title: Gravitational Waves and Dark Sector: Connecting NANOGrav Pulsar Timing Data and Hubble Tension
Recent pulsar timing data reported by the NANOGrav collaboration may indicate the existence of a stochastic gravitational wave background around f∼10−8 Hz. We explore a possibility to generate such low-frequency gravitational waves from a dark sector phase transition. Assuming that the dark sector is completely decoupled from the visible sector except via the gravitational interaction, we find that some amount of dark radiation should remain until present. The NANOGrav data implies that the amount of dark radiation is close to the current upper bound, which may help mitigate the so-called Hubble tension. If the existence of dark radiation is not confirmed in the future CMB-S4 experiment, it would imply the existence of new particles feebly interacting with the standard model sector at an energy scale of O(1 - 100) MeV.
TAMARIT, Carlos Technical University of Munich Title: Gravitational waves as a Big Bang thermometer
There is a guaranteed background of stochastic gravitational waves produced in the thermal plasma in the early universe. Its energy density per logarithmic frequency interval scales with the maximum temperature Tmax which the primordial plasma attained at the beginning of the standard hot big bang era. It peaks in the microwave range, at around (80 GHz )x[106.75/g*s(Tmax)]^1/3, where g*s(Tmax) is the effective number of entropy degrees of freedom in the primordial plasma at Tmax. We present a state-of-the-art prediction of this Cosmic Gravitational Microwave Background (CGMB) for general models, and carry out calculations for the case of the Standard Model (SM) as well as for several of its extensions. On the side of minimal extensions we consider the Neutrino Minimal SM (νMSM) and the SM-Axion-Seesaw-Higgs portal inflation model (SMASH), which provide a complete and consistent cosmological history including inflation. As an example of a non-minimal extension of the SM we consider the Minimal Supersymmetric Standard Model (MSSM). Furthermore, we discuss the current upper limits and the prospects to detect the CGMB in laboratory experiments and thus measure the maximum temperature and the effective number of degrees of freedom at the beginning of the hot big bang.
TERADA, Takahiro Institute for Basic Science Title: Minimal Supergravity Inflation without Slow Gravitino
Inflation in supergravity with minimal degrees of freedom utilizing orthogonal nilpotent superfields is known to lead to catastrophic production of slow gravitinos provided that the description keeps valid after inflation. We will present an alternative formulation of minimal supergravity inflation circumventing the catastrophic production issue. This talk is based on arXiv:2104.05731 [hep-th]. Depending on the progress, we may add comments on Swampland conjectures on gravitino mass and speed.
TODA, Yo Hokkaido University Title: Hubble tension with an extra radiation and neutrino degeneracy
The standard Lambda CDM cosmological model now seems to face some puzzles. One of the most serious problems is the so-called Hubble tension; the values of the Hubble constant obtained by local measurements look inconsistent with that inferred from CMB. Although introducing extra radiations such as hot axions or sterile neutrinos appears to be promising, such extra radiations increase the Helium mass fraction synthesized by Big Bang Nucleosynthesis (BBN). To cancel such an increment, positive electron neutrino asymmetry may be also needed. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae, we evaluate the possibility of non-zero asymmetry and extra radiations.
UCHIDA, Fumio RESCEU, University of Tokyo Title: Constraints on primordial magnetic fields from baryon isocurvature perturbations.
Magnetic fields are ubiquitous in the universe, and even in the voids, where few astrophysical objects that could amplify seed fields through e.g., the galactic dynamo exist, lower bounds of the strength of the so-called intergalactic magnetic fields are observationally suggested. A possibility is that such cosmological magnetic fields originate in the very early universe. In the talk, we assume primordial magnetic fields before the electroweak symmetry breaking and argue that such fields unavoidably generate baryon isocurvature perturbations through a conversion from magnetic helicity to baryon number through the chiral anomaly in the Standard Model. For successful big-bang nucleosynthesis is a constraint put on the baryon isocurvature perturbations, and hence we can constrain the properties of the primordial magnetic fields. The condition is so strong that the intergalactic magnetic fields cannot be purely primordial and that some mechanisms of amplification or generation of magnetic fields after the electroweak symmetry breaking are needed.
VELASCO, Liliana KIAS Title: Tracking Down the Route to the SM with Inflation and Gravitational Waves
Abstract: The extraordinary epoch of gravitational wave (GW) detection is yet to reach its top. During the next few years, the interferometers KAGRA and LIGO-India will be integrated in the LIGO and Virgo interferometer network. Thanks to the improved sensitivity, this network will catch a huge number of events. Their detection will be so frequent that most of them will not be separated in time, and their signals are going to be too  entangled to identify.  All these  unresolvable events will  be detected as a Stochastic Gravitational Wave Background (SGWB). This is intriguing because these properties are also the characteristics GW signals  created by the physical processes occurring at the earliest moments of the universe.
Therefore,  model building within the context of Grand Unified Theories (GUT) needs to make an effort to provide a compelling science case for scenarios where neither the cosmological nor the astrophysical contribution dominates over the other,  making the identification of GW predicted by GUT indeed possible to be resolved among all the SGWB. We make a survey of GUT models with different sources of SGWB at different scales to point out that a particular breaking chain down to the SM would lead its imprint in SGWB making then possible to discern among  the many possible chain routes.  We point out which current theoretical uncertainties in the mechanisms and codes for computing First Order Phase Transitions, cosmic strings and domain walls parameters need to be improved in order to truly identify the particular breaking chains down to the SM.
YAMADA, Masaki Tohoku University Title: Cosmic Birefringence Triggered by Dark Matter Domination
Abstract: Cosmic birefringence is predicted if an axion-like particle (ALP) moves after the recombination. We show that this naturally happens if the ALP is coupled to the dark matter density because it then acquires a large effective mass after the matter-radiation equality. We give a simple model to realize this scenario, where dark matter is made of hidden monopoles, which give the ALP such a large effective mass through the Witten effect. The mechanism works if the ALP decay constant is of order the GUT-scale without a fine-tuning of the initial misalignment angle.
YIN, Lu CQUeST Title: Can dark energy be dynamical?
We highlight shortcomings of the dynamical dark energy (DDE) paradigm. For parametric models with
equation of state (EOS), w(z) = w0 + wa f(z) for a given function of redshift f(z), we show that the errors in wa are sensitive to f(z): if f(z) increases quickly with redshift z, then errors in wa are smaller, and vice versa. As a result, parametric DDE models suffer from a degree of arbitrariness and focusing too much on one model runs that risk that DDE may be overlooked. In particular, we show the ubiquitous Chevallier-Polarski-Linder model is one of the least sensitive to DDE. We also comment on “wiggles” in w(z) uncovered in non-parametric reconstructions. Concretely, we isolate the most relevant Fourier modes in the wiggles, model them and fit them back to the original data to confirm the wiggles at . 2σ. We delve into the assumptions going into the reconstruction and argue that the assumed correlations, which clearly influence the wiggles, place strong constraints on field theory models of DDE.