500 research outputs found
Homeopathic Dark Matter, or how diluted heavy substances produce high energy cosmic rays
We point out that current and planned telescopes have the potential of
probing annihilating Dark Matter (DM) with a mass of O(100) TeV and beyond. As
a target for such searches, we propose models where DM annihilates into lighter
mediators, themselves decaying into Standard Model (SM) particles. These models
allow to reliably compute the energy spectra of the SM final states, and to
naturally evade the unitarity bound on the DM mass. Indeed, long-lived
mediators may cause an early matter-dominated phase in the evolution of the
Universe and, upon decaying, dilute the density of preexisting relics thus
allowing for very large DM masses. We compute this dilution in detail and
provide results in a ready-to-use form. Considering for concreteness a model of
dark U(1) DM, we then study both dilution and the signals at various high
energy telescopes observing gamma rays, neutrinos and charged cosmic rays. This
study enriches the physics case of these experiments, and opens a new
observational window on heavy new physics sectors.Comment: 39 pages, 11 figures. v2: reference added, fixed technical issue
causing 2 figures not to show properly. v3: BBN constraints amended,
conclusions unchanged. Matches published versio
First-order Phase Transition interpretation of PTA signal produces solar-mass Black Holes
We perform a Bayesian analysis of NANOGrav 15yr and IPTA DR2 pulsar timing
residuals and show that the recently detected stochastic gravitational-wave
background (SGWB) is compatible with a SGWB produced by bubble dynamics during
a cosmological first-order phase transition. The timing data suggests that the
phase transition would occur around QCD confinement temperature and would have
a slow rate of completion. This scenario can naturally lead to the abundant
production of primordial black holes (PBHs) with solar masses. These PBHs can
potentially be detected by current and advanced gravitational wave detectors
LIGO-Virgo-Kagra, Einstein Telescope, Cosmic Explorer, by astrometry with GAIA
and by 21-cm survey.Comment: 5 pages, 4 figures + appendice
Domain wall interpretation of the PTA signal confronting black hole overproduction
Recently, Pulsar Timing Array (PTA) collaborations have detected a stochastic
gravitational wave background (SGWB) at nano-Hz frequencies, with Domain Wall
networks (DWs) proposed as potential sources. To be cosmologically viable, they
must annihilate before dominating the universe energy budget, thus generating a
SGWB. While sub-horizon DWs shrink and decay rapidly, causality requires DWs
with super-horizon size to continue growing until they reach the Hubble
horizon. Those entering the latest can be heavier than a Hubble patch and
collapse into Primordial Black Holes (PBHs). By applying percolation theory, we
pioneer an estimation of the PBH abundance originating from DW networks. We
conduct a Bayesian analysis of the PTA signal, interpreting it as an outcome of
SGWB from DW networks, accounting for PBH overproduction as a prior. We
included contributions from supermassive black hole binaries along with their
astrophysical priors. Our findings indicate that DWs, as the proposed source of
the PTA signal, result in the production of PBHs about ten times heavier than
the sun. The binary mergers occurring within these PBHs generate a second SGWB
in the kilo-Hz domain which could be observable in on-going or planned
Earth-based interferometers if the correlation length of the DW network is
greater than approximately 60 than the cosmic horizon, .Comment: Major improvements of the PBH formation modeling, of the depth of the
Bayesian analysis and of the SMBH binary prior (5 pages, 4 figures +
appendix, 21 pages in total
Primordial Black Holes and Wormholes from Domain Wall Networks
Domain walls (DWs) are topological defects originating from phase transitions
in the early universe. In the presence of an energy imbalance between distinct
vacua, enclosed DW cavities shrink until the entire network disappears. By
studying the dynamics of thin-shell bubbles in General Relativity, we
demonstrate that closed DWs with sizes exceeding the cosmic horizon tend to
annihilate later than the average. This delayed annihilation allows for the
formation of large overdensities, which, upon entering the Hubble horizon,
eventually collapse to form Primordial Black Holes (PBHs). We rely on 3D
percolation theory to calculate the number density of these late-annihilating
DWs, enabling us to infer the abundance of PBHs. A key insight from our study
is that DW networks with the potential to emit observable Gravitational Waves
are also likely to yield detectable PBHs. Additionally, we study the production
of wormholes connected to baby-universes and conclude on the possibility to
generate a multiverse.Comment: 11 pages, 7 figures, and appendi
Primordial Black Holes from Supercooled Phase Transitions
Cosmological first-order phase transitions (1stOPTs) are said to be strongly
supercooled when the nucleation temperature is much smaller than the critical
temperature. These are often encountered in theories that admit a nearly
scale-invariant potential, for which the bounce action decreases only
logarithmically with temperature. During supercooled 1stOPTs the equation of
state of the universe undergoes a rapid and drastic change, transitioning from
vacuum-domination to radiation-domination. The statistical variations in bubble
nucleation histories imply that distinct causal patches percolate at slightly
different times. Patches which percolate the latest undergo the longest
vacuum-domination stage and as a consequence develop large over-densities
triggering their collapse into primordial black holes (PBHs). We derive an
analytical approximation for the probability of a patch to collapse into a PBH
as a function of the 1stOPT duration, , and deduce the expected PBH
abundance. We find that 1stOPTs which take more than of a Hubble time to
complete () produce observable PBHs. Their abundance is
independent of the duration of the supercooling phase, in agreement with the de
Sitter no hair conjecture.Comment: Main text: 6 pages, 5 figures, Appendices: 12 pages, 6 figures, v2:
references added and a typo correcte
Friction pressure on relativistic bubble walls
During a cosmological first-order phase transition, particles of the plasma crossing the bubble walls can radiate a gauge boson. The resulting pressure cannot be computed perturbatively for large coupling constant and/or large supercooling. We resum the real and virtual emissions at all leading-log orders, both analytically and numerically using a Monte-Carlo simulation. We find that radiated bosons are dominantly soft and that the resulting retarding pressure on relativistic bubble walls is linear both in the Lorentz boost and in the order parameter, up to a log. We further quantitatively discuss IR cut-offs, wall thickness effects, the impact of various approximations entering the calculation, and comment on the fate of radiated bosons that are reflected
String fragmentation in supercooled confinement and implications for dark matter
A strongly-coupled sector can feature a supercooled confinement transition in the early universe. We point out that, when fundamental quanta of the strong sector are swept into expanding bubbles of the confined phase, the distance between them is large compared to the confinement scale. We suggest a modelling of the subsequent dynamics and find that the flux linking the fundamental quanta deforms and stretches towards the wall, producing an enhanced number of composite states upon string fragmentation. The composite states are highly boosted in the plasma frame, which leads to additional particle production through the subsequent deep inelastic scattering. We study the consequences for the abundance and energetics of particles in the universe and for bubble-wall Lorentz factors. This opens several new avenues of investigation, which we begin to explore here, showing that the composite dark matter relic density is affected by many orders of magnitude
Friction pressure on relativistic bubble walls
During a cosmological first-order phase transition, particles of the plasma
crossing the bubble walls can radiate a gauge boson. The resulting pressure
cannot be computed perturbatively for large coupling constant and/or large
supercooling. We resum the real and virtual emissions at all leading-log
orders, both analytically and numerically using a Monte-Carlo simulation. We
find that radiated bosons are dominantly soft and that the resulting retarding
pressure on relativistic bubble walls is linear both in the Lorentz boost and
in the order parameter, up to a log. We further quantitatively discuss IR
cut-offs, wall thickness effects, the impact of various approximations entering
the calculation, and comment on the fate of radiated bosons that are reflected.Comment: 26 pages, 8 figures, plus appendices and references. v2: additional
references added, matches JHEP publicatio
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
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