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SUMMARY:The Cluster Soft Excess\, Dark Radiation and a 0.1-1 keV Cosmic Ax
 ion Background - Joseph Conlan (Oxford)
DTSTART:20131021T120000Z
DTEND:20131021T130000Z
UID:TALK48204@talks.cam.ac.uk
CONTACT:33215
DESCRIPTION:Since 1996 soft excess emission above thermal bremsstrahlung f
 rom the intracluster medium \nhas been observed from galaxy clusters in ex
 treme ultraviolet and soft X-ray frequencies. \nWe review proposed astroph
 ysical explanations\, and the difficulties they face in the light of clust
 er magnetic field measurements \nand null observations of clusters in gamm
 a rays. String theory moduli that decay at t ~ 10^-6^ s generally have non
 -zero branching ratios\nto axion-like particles. These freestream to the p
 resent day and currently constitute a dark radiation Cosmic Axion Backgrou
 nd at\n0.1 - 1 keV energies.  These axions can convert into photons in clu
 ster magnetic fields\, and \nallowed particle physics parameters can easil
 y generate the required excess luminosity of approximately 10^43^ erg s^-1
 ^.\nFor the case of Coma\, we use a detailed model of the Coma magnetic fi
 eld\nto calculate the axion conversion probabilities and to study the resu
 lting excess morphology.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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