524 research outputs found
Solitosynthesis induced phase transitions
We consider a phase transition induced by the growth of Q-balls in a false
vacuum. Such a transition could occur in the early universe in the case of
broken supersymmetry with a metastable false vacuum. Small Q-balls with a
negative potential energy can grow in a false vacuum by accretion of global
charge until they reach critical size, expand, and cause a phase transition. We
consider the growth of Q-balls from small to large, using the Bethe-Salpeter
equation to describe small charge solitons and connecting to the growth of
larger solitons for which the semiclassical approximation is reliable. We thus
test the scenario in a simplified example inspired by supersymmetric extensions
of the standard model.Comment: 14 pages, 9 figures, 2 tables Added sections on explicit connection
between Q-balls and squark and higgs field
Signals from dark atom formation in halos
We consider indirect detection signals of atomic dark matter, with a massive
dark photon which mixes kinetically with hypercharge. In significant regions of
parameter space, dark matter remains at least partially ionized today, and dark
atom formation can occur efficiently in dense regions, such as the centers of
galactic halos. The formation of dark atoms is accompanied by emission of a
dark photon, which can subsequently decay into Standard Model particles. We
discuss the expected signal strength and compare it to that of annihilating
dark matter. As a case study, we explore the possibility that dark atom
formation can account for the observed 511 keV line and outline the relevant
parameter space.Comment: 14 pages, 10 figure
Leptogenesis via Higgs Condensate Relaxation
An epoch of Higgs relaxation may occur in the early universe during or
immediately following postinflationary reheating. It has recently been pointed
out that leptogenesis may occur in minimal extensions of the Standard Model
during this epoch. We analyse Higgs relaxation taking into account the effects
of perturbative and non-perturbative decays of the Higgs condensate, and we
present a detailed derivation of the relevant kinetic equations and of the
relevant particle interaction cross sections. We identify the parameter space
in which a sufficiently large asymmetry is generated.Comment: 18 pages, 14 figure
Self-interacting asymmetric dark matter coupled to a light massive dark photon
Dark matter (DM) with sizeable self-interactions mediated by a light species
offers a compelling explanation of the observed galactic substructure;
furthermore, the direct coupling between DM and a light particle contributes to
the DM annihilation in the early universe. If the DM abundance is due to a dark
particle-antiparticle asymmetry, the DM annihilation cross-section can be
arbitrarily large, and the coupling of DM to the light species can be
significant. We consider the case of asymmetric DM interacting via a light (but
not necessarily massless) Abelian gauge vector boson, a dark photon. In the
massless dark photon limit, gauge invariance mandates that DM be
multicomponent, consisting of positive and negative dark ions of different
species which partially bind in neutral dark atoms. We argue that a similar
conclusion holds for light dark photons; in particular, we establish that the
multi-component and atomic character of DM persists in much of the parameter
space where the dark photon is sufficiently light to mediate sizeable DM
self-interactions. We discuss the cosmological sequence of events in this
scenario, including the dark asymmetry generation, the freeze-out of
annihilations, the dark recombination and the phase transition which gives mass
to the dark photon. We estimate the effect of self-interactions in DM haloes,
taking into account this cosmological history. We place constraints based on
the observed ellipticity of large haloes, and identify the regimes where DM
self-scattering can affect the dynamics of smaller haloes, bringing theory in
better agreement with observations. Moreover, we estimate the cosmological
abundance of dark photons in various regimes, and derive pertinent bounds.Comment: v3: published versio
Leptogenesis Via Neutrino Production During Higgs Condensate Relaxation
During inflation, scalar fields, including the Higgs boson, may acquire a
nonzero vacuum expectation value, which must later relax to the equilibrium
value during reheating. In the presence of the time-dependent condensate, the
vacuum state can evolve into a state with a nonzero particle number. We show
that, in the presence of lepton number violation in the neutrino sector, the
particle production can explain the observed matter-antimatter asymmetry of the
universe. We find that this form of leptogenesis is particularly effective when
the Higgs condensate decays rapidly and at low reheat scale. As part of the
calculation, we present some exact results for the Bogoliubov transformations
for Majorana fermions with a nonzero time-dependent chemical potential, in
addition to a time-dependent mass.Comment: 19 pages, 3 figure
Gravitational waves from fermion production during axion inflation
We present analytic results for the gravitational wave power spectrum induced
in models where the inflaton is coupled to a fermionic pseudocurrent. We show
that although such a coupling creates helically polarized fermions, the
polarized component of the resulting gravitational waves is parametrically
suppressed with respect to the non-polarized one. We also show that the
amplitude of the gravitational wave signal associated to this production cannot
exceed that generated by the standard mechanism of amplification of vacuum
fluctuations. We previously found that this model allows for a regime in which
the backreaction of the produced fermions allows for slow-roll inflation even
for a steep inflaton potential, and still leads to Gaussian primordial scalar
perturbations. The present analysis shows that this regime also results in a
gravitational wave signal compatible with the current bounds.Comment: 29 pages, 2 figure
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