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SUMMARY:Right-handed Neutrinos and the (Dark Sector of the) Universe
DTSTART;VALUE=DATE-TIME:20130215T140000Z
DTEND;VALUE=DATE-TIME:20130215T150000Z
DTSTAMP;VALUE=DATE-TIME:20260627T115704Z
UID:indico-event-1892@indico.ific.uv.es
DESCRIPTION:I discuss the role of neutrinos\, in particular right-handed s
 terile ones\, in contributing to the dark sector of the Universe\, especia
 lly in playing the role of dark matter. I start from a simplest extension 
 of the standard model\, proposed by Shaposhnikov and collaborators\, which
  involves three right-handed Majorana massive neutrinos\, and exploit astr
 ophysical and cosmological constraints on the lowest of these extra states
  in order for it to be the dark matter candidate. This is consistent with 
 current constraints\, provided the mass of the lightest right-handed neutr
 ino is of order of a few keV. I discuss mechanisms for which a mass of suc
 h an order can be generated. One of such mechanisms can be via non-perturb
 ative effects\, when axions (pseudoscalar fields) couple to fermions via c
 hirality-changing Yukawa couplings with appropriately suppressed coefficie
 nts. In such theories\, an effective right-handed Majorana neutrino mass c
 an be generated at two loops by gravitational interactions that involve gl
 obal anomalies related to quantum torsion\, associated with a totally anti
 symmetric tensor field that exist in the gravitational multiplet of quantu
 m gravity theories\, such as strings\, or in general loop quantum gravity 
 models that are known to have torsion. The gravitational torsion in four s
 pace-time dimensions is equivalent to the existence of a Kalb-Ramond pesud
 oscalar field\, which upon mixing with ordinary axions gives rise to Major
 ana neutrino masses as above. We estimate the magnitude of such gravitatio
 nally-induced Majorana right-handed neutrino masses and find that it is hi
 ghly model dependent\, ranging from multi-TeV to keV scales\, the latter r
 ange being the one that makes such heavy neutrinos dark matter candidates.
 \n\nhttps://indico.ific.uv.es/event/1892/
LOCATION:Dpto. de Física Teórica (UVEG) Sala Seminarios
URL:https://indico.ific.uv.es/event/1892/
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