55 research outputs found
Generation of Asymmetric Dark Matter and Gravitational Waves
We consider the possibility of a gravitational wave signal in an asymmetric
dark matter model. In this model a generative sector produces both the baryon
asymmetry and a dark matter asymmetry in a strong first-order phase transtion.
Bubble collisions during the phase transition lead to sound waves in the plasma
which are a source of a stochastic gravitational wave background. We consider
the prospects of future graviational wave observatories such as LISA and BBO
detecting such a signal. Constraints on the model from Halo ellipticity,
and direct detection experiments are also discussed.Comment: 4 pages, 3 figures. Prepared for the proceedings of the 29th
Rencontres de Blois on Particle Physics and Cosmolog
Gravitational waves from the asymmetric-dark-matter generating phase transition
The baryon asymmetry, together with a dark matter asymmetry, may be produced
during a first order phase transition in a generative sector. We study the
possibility of a gravitational wave signal in a model realising such a
scenario. We identify areas of parameter space with strong phase transitions
which can be probed by future, space based, gravitational wave detectors. Other
signals of this scenario include collider signatures of a , DM self
interactions, a contribution to and nuclear recoils at
direct detection experiments.Comment: 23 pages, 3 figures. V2: corrected typo, added references. V3: small
corrections, added reference
Asymmetric thermal-relic dark matter: Sommerfeld-enhanced freeze-out, annihilation signals and unitarity bounds
Dark matter that possesses a particle-antiparticle asymmetry and has
thermalised in the early universe, requires a larger annihilation cross-section
compared to symmetric dark matter, in order to deplete the dark antiparticles
and account for the observed dark matter density. The annihilation
cross-section determines the residual symmetric component of dark matter, which
may give rise to annihilation signals during CMB and inside haloes today. We
consider dark matter with long-range interactions, in particular dark matter
coupled to a light vector or scalar force mediator. We compute the couplings
required to attain a final antiparticle-to-particle ratio after the thermal
freeze-out of the annihilation processes in the early universe, and then
estimate the late-time annihilation signals. We show that, due to the
Sommerfeld enhancement, highly asymmetric dark matter with long-range
interactions can have a significant annihilation rate, potentially larger than
symmetric dark matter of the same mass with contact interactions. We discuss
caveats in this estimation, relating to the formation of stable bound states.
Finally, we consider the non-relativistic partial-wave unitarity bound on the
inelastic cross-section, we discuss why it can be realised only by long-range
interactions, and showcase the importance of higher partial waves in this
regime of large inelasticity. We derive upper bounds on the mass of symmetric
and asymmetric thermal-relic dark matter for s-wave and p-wave annihilation,
and exhibit how these bounds strengthen as the dark asymmetry increases.Comment: 31 pages, 8 figures. V2: small corrections, added discussion and
reference
Hot and Heavy Dark Matter from Supercooling
We point out that dark matter which is produced non-adiabatically in a phase
transition (PT) with fast bubble walls receives a boost in velocity which leads
to long free-streaming lengths. We find that this could be observed via the
suppressed matter power spectrum for dark matter masses around
GeV and energy scales of the PT around . The PT should
take place at the border of the supercooled regime, i.e. approximately when the
Universe becomes vacuum dominated. This work offers novel physics goals for
galaxy surveys, Lyman-, lensing, and 21-cm observations, and connects
these to the gravitational waves from such phase transitions, and more
speculatively to possible telescope signals of heavy dark matter decays.Comment: 5 pages plus appendice
Particle-antiparticle asymmetries from annihilations
An extensively studied mechanism to create particle-antiparticle asymmetries
is the out-of-equilibrium and CP violating decay of a heavy particle. Here we
instead examine how asymmetries can arise purely from 2 2 annihilations
rather than from the usual 1 2 decays and inverse decays. We review the
general conditions on the reaction rates that arise from S-matrix unitarity and
CPT invariance, and show how these are implemented in the context of a simple
toy model. We formulate the Boltzmann equations for this model, and present an
example solution.Comment: 5 pages, v2: added reference, v3: some changes to text in response to
comment
Non-Cold Dark Matter from Primordial Black Hole Evaporation
Dark matter coupled solely gravitationally can be produced through the decay
of primordial black holes in the early universe. If the dark matter is lighter
than the initial black hole temperature, it could be warm enough to be subject
to structure formation constraints. In this paper we perform a more precise
determination of these constraints. We first evaluate the dark matter
phase-space distribution, without relying on the instantaneous decay
approximation. We then interface this phase-space distribution with the
Boltzmann code CLASS to extract the corresponding matter power spectrum, which
we find to match closely those of warm dark matter models, albeit with a
different dark matter mass. This mapping allows us to extract constraints from
Lyman- data without the need to perform hydrodynamical simulations. We
robustly rule out the possibility, consistent with previous analytic estimates,
of primordial black holes having come to dominate the energy density of the
universe and simultaneously given rise to all the DM through their decay.
Consequences and implications for dark radiation and leptogenesis are also
briefly discussed.Comment: 33 pages, 4 figure
Primordial black holes as dark matter: Interferometric tests of phase transition origin
We show that primordial black holes - in the observationally allowed mass
window with - formed from late nucleating patches in a first
order phase transition imply upcoming gravitational wave interferometers will
see a large stochastic background arising from the bubble collisions. As an
example, we use a classically scale invariant model, in which the right
handed neutrinos explain the neutrino masses and leptogenesis, and the dark
matter consists of primordial black holes. The conclusion regarding the
gravitational waves is, however, expected to hold model independently for black
holes coming from such late nucleating patches.Comment: 33 page
Baryon Number Violating Scalar Diquarks at the LHC
Baryon number violating (BNV) processes are heavily constrained by
experiments searching for nucleon decay and neutron-antineutron oscillations.
If the baryon number violation occurs via the third generation quarks, however,
we may be able to avoid the nucleon stability constraints, thus making such BNV
interactions accessible at the LHC. In this paper we study a specific class of
BNV extensions of the standard model (SM) involving diquark and leptoquark
scalars. After an introduction to these models we study one promising extension
in detail, being interested in particles with mass of O(TeV). We calculate
limits on the masses and couplings from neutron-antineutron oscillations and
dineutron decay for couplings to first and third generation quarks. We explore
the possible consequences of such a model on the matter-antimatter asymmetry.
We shall see that for models which break the global baryon minus lepton number
symmetry, (B-L), the most stringent constraints come from the need to preserve
a matter-antimatter asymmetry. That is, the BNV interaction cannot be
introduced if it would remove the matter-antimatter asymmetry independent of
baryogenesis mechanism and temperature. Finally, we examine the phenomenology
of such models at colliders such as the LHC.Comment: 10 pages, 9 figures. v2: references added, some typos corrected. v3:
some small corrections to match published version, no change in conclusion
Asymmetric dark matter: residual annihilations and self-interactions
Dark matter (DM) coupled to light mediators has been invoked to resolve the
putative discrepancies between collisionless cold DM and galactic structure
observations. However, -ray searches and the CMB strongly constrain
such scenarios. To ease the tension, we consider asymmetric DM. We show that,
contrary to the common lore, detectable annihilations occur even for large
asymmetries, and derive bounds from the CMB, -ray, neutrino and
antiproton searches. We then identify the viable space for self-interacting DM.
Direct detection does not exclude this scenario, but provides a way to test it.Comment: 20 pages, 4 figure
- …