Saxion cosmology for thermalized gravitino dark matter

Abstract

In all supersymmetric theories, gravitinos, with mass suppressed by the Planck scale, are an obvious candidate for dark matter; but if gravitinos ever reached thermal equilibrium, such dark matter is apparently either too abundant or too hot, and is excluded. However, in theories with an axion, a saxion condensate is generated during an early era of cosmological history and its late decay dilutes dark matter. We show that such dilution allows previously thermalized gravitinos to account for the observed dark matter over very wide ranges of gravitino mass, keV < m 3/2 < TeV, axion decay constant, 10 9 GeV < f a < 10 16 GeV, and saxion mass, 10 MeV < m s < 100 TeV. Constraints on this parameter space are studied from BBN, supersymmetry breaking, gravitino and axino production from freeze-in and saxion decay, and from axion production from both misalignment and parametric resonance mechanisms. Large allowed regions of (m 3/2 , f a , m s ) remain, but differ for DFSZ and KSVZ theories. Superpartner production at colliders may lead to events with displaced vertices and kinks, and may contain saxions decaying to (W W, ZZ, hh), gg, γγ or a pair of Standard Model fermions. Freeze-in may lead to a sub-dominant warm component of gravitino dark matter, and saxion decay to axions may lead to dark radiation.

QCD Axion Dark Matter with a Small Decay Constant

“…For sufficiently large m H , saxions are still in thermal equilibrium while nonrelativistic and, hence, disappear without leaving any imprint by decaying into standard model fermions. Saxion masses below Oð10Þ MeV are, however, excluded, for the f a of interest, from saxion cooling of supernovae [33][34][35][36][37]56]. For small m H , on the other hand, saxions decouple from the thermal bath while relativistic, and decay dominantly to a pair of axions at temperature…”

When the universe expands too fast: relentless dark matter

“…* Electronic address: fderamo@ucsc.edu † Electronic address: nfernan2@ucsc.edu ‡ Electronic address: profumo@ucsc.edu However, we have no direct information about the energy budget of the universe at higher temperatures. The WIMP DM thermal relic abundance may differ by orders of magnitude if deviations from a standard cosmological history are considered [10][11][12][13][14][15][16][17][18][19][20][21][22].…”

Searching for metastable particles with sub-millimeter displaced vertices at hadron colliders

“…For instance, in supersymmetric (SUSY) models, gluino tends to be long-lived if sfermion masses are in the multi-TeV range [2][3][4]. Such a long-lived particle is also found in the gauge-mediation models [5][6][7][8], in R-parity violating models [9][10][11], in SUSY axion models [12][13][14][15][16][17][18], in the stealth SUSY scenario [19][20][21], in the SUSY relaxion models [22,23], and in a degenerate SUSY spectrum [24][25][26][27][28][29][30][31][32][33][34]. Other well-motivated scenarios such as Neutral Naturalness [35][36][37][38][39], hidden-valley models [40][41][42][43][44], composite Higgs models [45], dark matter models [46][47][48]…”