1,390 research outputs found
Sub-GeV Dark Matter Shining at Future MeV Gamma-Ray Telescopes
We propose a novel framework where light (sub-GeV) dark matter (DM) is
detectable with future MeV gamma-ray telescopes without conflicting with Cosmic
Microwave Background (CMB) data. The stable DM particle has a very low
thermal relic abundance due to its large pair-annihilation cross section. The
DM number density is stored in a heavier, meta-stable partner with
suppressed pair-annihilation rates, that does not perturb the CMB, and whose
late-time decays fill the universe with DM
particles. We provide explicit, model-independent realizations for this
framework, and discuss constraints on late-time decays, and thus on parameters
of this setup, from CMB, Big Bang Nucleosynthesis, and Large Scale Structure.Comment: 6 pages, 3 figures, version published in Physical Review Letter
Surprises from Complete Vector Portal Theories: New Insights into the Dark Sector and its Interplay with Higgs Physics
We study UV complete theories where the Standard Model (SM) gauge group is
extended with a new abelian , and the field content is augmented by an
arbitrary number of scalar and fermion SM singlets, potentially including dark
matter (DM) candidates. Considerations such as classical and quantum gauge
invariance of the full theory and S-matrix unitarity, not applicable within a
simplified model approach, are shown to have significant phenomenological
consequences. The lack of gauge anomalies leads to compact relations among the
fermion charges, and puts a lower bound on the number of dark fermions.
Contrary to naive expectations, the DM annihilation to Zh is found to be p-wave
suppressed, as hinted by perturbative unitarity of S-matrix, with dramatic
implications for DM thermal relic density and indirect searches. Within this
framework, the interplay between dark matter, new vector boson and Higgs
physics is rather natural and generic.Comment: 5 pages, 3 figures; v2: minor corrections, references added, journal
versio
Imprint of a scalar era on the primordial spectrum of gravitational waves
Upcoming searches for the stochastic background of inflationary gravitational
waves (GWs) offer the exciting possibility to probe the evolution of our
Universe prior to Big Bang nucleosynthesis. In this spirit, we explore the
sensitivity of future GW observations to a broad class of
beyond-the-Standard-Model scenarios that lead to a nonstandard expansion
history. We consider a new scalar field whose coherent oscillations dominate
the energy density of the Universe at very early times, resulting in a scalar
era prior to the standard radiation-dominated era. The imprint of this scalar
era on the primordial GW spectrum provides a means to probe well-motivated yet
elusive models of particle physics. Our work highlights the complementarity of
future GW observatories across the entire range of accessible frequencies.Comment: 8 pages, 3 figures. v2: typos removed, updated references. v3:
matches version published in Phys. Rev. Researc
When the Universe Expands Too Fast: Relentless Dark Matter
We consider a modification to the standard cosmological history consisting of
introducing a new species whose energy density red-shifts with the scale
factor like . For , such a red-shift is
faster than radiation, hence the new species dominates the energy budget of the
universe at early times while it is completely negligible at late times. If
equality with the radiation energy density is achieved at low enough
temperatures, dark matter can be produced as a thermal relic during the new
cosmological phase. Dark matter freeze-out then occurs at higher temperatures
compared to the standard case, implying that reproducing the observed abundance
requires significantly larger annihilation rates. Here, we point out a
completely new phenomenon, which we refer to as dark
matter: for large enough , unlike the standard case where annihilation ends
shortly after the departure from thermal equilibrium, dark matter particles
keep annihilating long after leaving chemical equilibrium, with a significant
depletion of the final relic abundance. Relentless annihilation occurs for and for s-wave and p-wave annihilation, respectively, and it
thus occurs in well motivated scenarios such as a quintessence with a kination
phase. We discuss a few microscopic realizations for the new cosmological
component and highlight the phenomenological consequences of our calculations
for dark matter searches.Comment: 14 pages, 9 figure
New Constraints on Dark Matter Effective Theories from Standard Model Loops
We consider an effective field theory for a gauge singlet Dirac dark matter
(DM) particle interacting with the Standard Model (SM) fields via effective
operators suppressed by the scale TeV. We perform a
systematic analysis of the leading loop contributions to spin-independent (SI)
DM--nucleon scattering using renormalization group evolution between
and the low-energy scale probed by direct detection experiments. We find that
electroweak interactions induce operator mixings such that operators that are
naively velocity-suppressed and spin-dependent can actually contribute to SI
scattering. This allows us to put novel constraints on Wilson coefficients that
were so far poorly bounded by direct detection. Constraints from current
searches are comparable to LHC bounds, and will significantly improve in the
near future. Interestingly, the loop contribution we find is maximally isospin
violating even if the underlying theory is isospin conserving.Comment: 6 pages, 3 figures. v2: revised manuscript, updated formulas and
plots, improved bounds, references added, journal versio
Multiple Gamma Lines from Semi-Annihilation
Hints in the Fermi data for a 130 GeV gamma line from the galactic center
have ignited interest in potential gamma line signatures of dark matter.
Explanations of this line based on dark matter annihilation face a parametric
tension since they often rely on large enhancements of loop-suppressed cross
sections. In this paper, we pursue an alternative possibility that dark matter
gamma lines could arise from "semi-annihilation" among multiple dark sector
states. The semi-annihilation reaction with a single final state photon is
typically enhanced relative to ordinary annihilation into photon pairs.
Semi-annihilation allows for a wide range of dark matter masses compared to the
fixed mass value required by annihilation, opening the possibility to explain
potential dark matter signatures at higher energies. The most striking
prediction of semi-annihilation is the presence of multiple gamma lines, with
as many as order N^3 lines possible for N dark sector states, allowing for dark
sector spectroscopy. A smoking gun signature arises in the simplest case of
degenerate dark matter, where a strong semi-annihilation line at 130 GeV would
be accompanied by a weaker annihilation line at 173 GeV. As a proof of
principle, we construct two explicit models of dark matter semi-annihilation,
one based on non-Abelian vector dark matter and the other based on retrofitting
Rayleigh dark matter.Comment: 15 pages of text, 8 figures. v2: refs adde
Jet Quenching Parameter via Soft Collinear Effective Theory (SCET)
We analyze the transverse momentum broadening in the absence of radiation of
an energetic parton propagating through quark-gluon plasma via Soft Collinear
Effective Theory (SCET). We show that the probability for picking up transverse
momentum k_\perp is given by the Fourier transform of the expectation value of
two transversely separated light-like path-ordered Wilson lines. The subtleties
about the ordering of operators do not change the \hat q value for the strongly
coupled plasma of N=4 SYM theory.Comment: 6 pages, 2 figures - Talk presented by F. D'Eramo at Jets in
Proton-Proton and Heavy-Ion Collisions, August 12-14, 2010, Prague, Czech
Republi
Finding the Scatterers in Hot Quark Soup
We present a brief report on a thought experiment in which an incident
energetic parton traverses a brick of quark-gluon plasma (QGP), see
arXiv:1808.03250 for the full report. We calculate the probability of detecting
a parton showing up at a large angle with respect to its initial direction due
to scattering with the constituents of QGP, using leading order perturbative
QCD. We include all relevant channels, including the Rutherford-like channel as
considered in early works, and those that are not Rutherford-like but become
important at a large angle. The resulting probability distributions contain
information about the short distance structure of QGP. Our results provide key
theoretical input toward finding the scatterers within the QGP liquid, which in
turn is the necessary first step toward using precise, high-statistics,
suitably differential measurements of jet modification in heavy ion collisions
to study the evolution of the properties of QGP with changing resolution scale.Comment: 5 pages, 4 figures, for the International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear Collisions, 30 September - 5
October 2018 in Aix-Les-Bains, Savoie, Franc
Multiverse Dark Matter: SUSY or Axions
The observed values of the cosmological constant {\it and} the abundance of
Dark Matter (DM) can be successfully understood, using certain measures, by
imposing the anthropic requirement that density perturbations go non-linear and
virialize to form halos. This requires a probability distribution favoring low
amounts of DM, i.e. low values of the PQ scale for the QCD axion and low
values of the superpartner mass scale for LSP thermal relics. In
theories with independent scanning of multiple DM components, there is a high
probability for DM to be dominated by a single component. For example, with
independent scanning of and , TeV-scale LSP DM and an axion
solution to the strong CP problem are unlikely to coexist. With thermal LSP DM,
the scheme allows an understanding of a Little SUSY Hierarchy with multi-TeV
superpartners. Alternatively, with axion DM, PQ breaking before (after)
inflation leads to typically below (below) the projected range of the
current ADMX experiment of GeV, providing strong
motivation to develop experimental techniques for probing lower .Comment: 32 pages, 14 figures, version published on JHE
Radiative PQ Breaking and the Higgs Boson Mass
The small and negative value of the Standard Model Higgs quartic coupling at
high scales can be understood in terms of anthropic selection on a landscape
where large and negative values are favored: most universes have a very
short-lived electroweak vacuum and typical observers are in universes close to
the corresponding metastability boundary. We provide a simple example of such a
landscape with a Peccei-Quinn symmetry breaking scale generated through
dimensional transmutation and supersymmetry softly broken at an intermediate
scale. Large and negative contributions to the Higgs quartic are typically
generated on integrating out the saxion field. Cancellations among these
contributions are forced by the anthropic requirement of a sufficiently
long-lived electroweak vacuum, determining the multiverse distribution for the
Higgs quartic in a similar way to that of the cosmological constant. This leads
to a statistical prediction of the Higgs boson mass that, for a wide range of
parameters, yields the observed value within the 1 statistical
uncertainty of 5 GeV originating from the multiverse distribution. The
strong CP problem is solved and single-component axion dark matter is
predicted, with an abundance that can be understood from environmental
selection. A more general setting for the Higgs mass prediction is discussed.Comment: 30 pages, 10 figures; v2, JHEP versio
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