Cosmic neutrino absorption spectroscopy Gabriela Barenboim University of

Cosmic neutrino absorption spectroscopy Gabriela Barenboim University of Valencia

According to standard cosmology, neutrinos should be the most abundant particles in the Universe, after CMB photons.

The CMB neutrino is the oldest relic !!!

Resonant annihilation of extremely high neutrinos on background neutrinos through the reaction nn Z

The relic neutrino background The annihilation of e+ eg g at T 2 me 1 Me. V transferred entropy from e+ e- to g ´s and so heated g ´s leaving Tn = (4/11)1/3 Tg Neutrinos are fermions while photons are bosons, so at a common temperature nn = 3/4 ng rn = 7/8 rg

Today … nn 0 = ¾ (Tn / Tg)3 ng 0 = 112 cm-3 The temperature of a massless decoupled species scales as T 0 (1+z) The relic neutrino number density will be red-shifted as nn 0 (1+z)3

However, the effective relic neutrino density that an UHE neutrino would encounter while traversing the expanding Universe we live in, is the neutrino density per unit red shift

Cosmic neutrino spectroscopy The location of the absorption lines in the UHEn spectrum points to neutrino masses !!!

Good news !!! It is possible to detect the absolute masses and the flavor composition of the mass eigenstates through the detection of the dips It could be, assuming perfect energy resolution and flavour tagging Bad news !!! Integration over cosmic time (red-shift), unconventional neutrino histories, thermal history of the Universe…

The ideal(ized) experiment Ideal laboratory : we neglect the expansion of the Universe and relic neutrino temperature Ideal target: the cosmic neutrino attenuator is a very long uniform column of length L with the current relic density Ideal beam: the UHE neutrino beam is originated >100 Mpc and contains all neutrino flavors in sufficient numbers Ideal detector: detector with perfect energy resolution and flavour tagging

Normal hierarchy Inverted hierarchy

Resonant absorption energy (e. V) Annihilation cross section (e. V-2)

Normal hierarchy Inverted hierarchy

Absorption lines in an expanding Universe Ø Evolution of the relic neutrino density changes Ø The energy of the UHE neutrino is red-shifted

neutrino mass = 0. 1 e. V 0 z 4

neutrino mass = 0. 1 e. V 4 z 8

neutrino mass = 0. 1 e. V 8 z 12

neutrino mass = 0. 1 e. V 12 z 16

neutrino mass = 0. 1 e. V 16 z 20

neutrino mass = 0. 1 e. V 0 z 20

neutrino mass = 0. 1 e. V 0 z 20

Absorption lines in an expanding Universe Normal hierarchy Inverted hierarchy

Alternative thermal histories and the effect grows with red-shift !!!

Neutrino temperature neutrinos are moving targets

Neutrino temperature neutrinos are moving targets

when considering cosmic evolution, thermal motion has to be considered for m <. 1 e. V

Normal hierarchy Inverted hierarchy

Diagnostic potential of cosmic spectroscopy ØThe detection of relic neutrinos would be a major discovery ØAs a byproduct, in principle, cosmic neutrino spectroscopy could provide the value of the individual neutrino masses and mixings, unveiling neutrino properties or unconventional neutrino stories. ØThe red-shift dependence is both a blessing and a curse…it shifts the dips to lower energies but gets them distorted, compromising the determination of neutrino masses. ØWith external information, neutrino spectroscopy can tell us about thermal history of the Universe.