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SUMMARY:[JC] CMB Birefringence from Axion String Networks Calibrated to an
  AMR Simulation
DTSTART:20260903T060000Z
DTEND:20260903T070000Z
DTSTAMP:20260916T145800Z
UID:indico-event-1402@indico.ibs.re.kr
DESCRIPTION:Speakers: Taehyun Jung\n\nIn this talk\, I will review the rec
 ent paper (2608.24456)\, where the authors studied CMB birefringence from 
 axion string networks and obtained a strong constraint on the axion-to-pho
 ton-photon anomaly coefficient for an ultra-light axion (mass < 10^-33 eV)
 . I will briefly introduce birefringence induced by an axion background an
 d the evolution of the axion string network. Then\, I will explain how the
  authors model the axion string evolution with parameters informed by the 
 AMR simulation (2412.08699) and obtain the constraint. For your informatio
 n\, I leave the abstract of the paper below.Abstract of the paper:  A cos
 mological network of axion strings may exist in the Universe today. If axi
 on-like particles couple to electromagnetism\, such a network induces spat
 ially varying birefringence in the polarization of the cosmic microwave ba
 ckground (CMB)\, which can be probed by current and next-generation CMB ex
 periments. We calibrate a loop-crossing model against a large-scale adapti
 ve-mesh-refinement (AMR) simulation of axion-string network dynamics in th
 e early Universe and use the calibrated model to predict CMB birefringence
  from recombination to today. We find that the non-detection of anisotropi
 c birefringence in CMB observations places a strong upper bound on the ele
 ctromagnetic anomaly coefficient A that enters the axion-photon coupling g
 aγγ = −Aαem/πfa. A joint analysis of available anisotropic birefring
 ence measurements constrains |A| < 0.24 at 95% C.L.\, which is independent
  of the Peccei-Quinn scale fa\, assuming that the axions are hyperlight so
  that the network survives until today. This limit strongly restricts the 
 high-energy embedding of hyperlight axions\, excluding the minimal Grand U
 nified Theory prediction for the electromagnetic anomaly coefficient at hi
 gh significance. In addition\, we discuss implications for an axion string
  origin of the recently reported evidence for isotropic birefringence.\n\n
 https://indico.ibs.re.kr/event/1402/
LOCATION:CTPU seminar room (IBS)
URL:https://indico.ibs.re.kr/event/1402/
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