35 research outputs found
Weak Scale Baryogenesis in a Supersymmetric Scenario with R-parity violation
We investigate the connection between R-parity violation (RPV) in
supersymmetric models and Baryogenesis. First we discuss in detail the
assumptions of a theorem by Nanopoulos and Weinberg on the CP asymmetry
generated from the decay of massive particles. In light of this statement, we
analyse some interesting models of Baryogenesis through RPV. We then explore,
in the context of RPV SUSY, the possibility to generate the baryon asymmetry
through the out-of-equilibrium decay of a metastable Weakly Interacting Massive
Particle (WIMP), as proposed in \cite{Cui:2012jh}. This setting is also
motivated by the observed coincidence between the abundances of dark and
baryonic matter. In this framework, we propose two models of out-of-equilibrium
decay of a would-be cold relic, and compute the associated CP asymmetry. With a
TeV-scale parent, the observed baryon abundance can be reproduced in these
models when the stop is in the multi-TeV region. Furthermore, annihilation of
the metastable particle into SM states must be characterised by a very weak
coupling, and by a heavy mediator TeV. These
models can also accommodate stop masses far from the TeV scale, at the expense
of weakening the explanation of the coincidence.Comment: 31 pages, 12 figures. Revised version according to JHEP requirements:
quantitative analyses added in Sec. 4, extended and revised list of refs,
abstract and conclusions clarifie
Axion Monodromy and the Weak Gravity Conjecture
Axions with broken discrete shift symmetry (axion monodromy) have recently
played a central role both in the discussion of inflation and the `relaxion'
approach to the hierarchy problem. We suggest a very minimalist way to
constrain such models by the weak gravity conjecture for domain walls: While
the electric side of the conjecture is always satisfied if the
cosine-oscillations of the axion potential are sufficiently small, the magnetic
side imposes a cutoff, , independent of the height
of these `wiggles'. We compare our approach with the recent related proposal by
Ibanez, Montero, Uranga and Valenzuela. We also discuss the non-trivial
question which version, if any, of the weak gravity conjecture for domain walls
should hold. In particular, we show that string compactifications with branes
of different dimensions wrapped on different cycles lead to a `geometric weak
gravity conjecture' relating volumes of cycles, norms of corresponding forms
and the volume of the compact space. Imposing this `geometric conjecture',
e.g.~on the basis of the more widely accepted weak gravity conjecture for
particles, provides at least some support for the (electric and magnetic)
conjecture for domain walls.Comment: 22 pages, 2 figures; v2: references added, typos corrected; v3:
published version + minor clarifications on self dual flux in Sec. 3.
Tuning and Backreaction in F-term Axion Monodromy Inflation
We continue the development of axion monodromy inflation, focussing in
particular on the backreaction of complex structure moduli. In our setting, the
shift symmetry comes from a partial large complex structure limit of the
underlying type IIB orientifold or F-theory fourfold. The coefficient of the
inflaton term in the superpotential has to be tuned small to avoid conflict
with Kahler moduli stabilisation. To allow such a tuning, this coefficient
necessarily depends on further complex structure moduli. At large values of the
inflaton field, these moduli are then in danger of backreacting too strongly.
To avoid this, further tunings are necessary. In weakly coupled type IIB theory
at the orientifold point, implementing these tunings appears to be difficult if
not impossible. However, fourfolds or models with mobile D7-branes provide
enough structural freedom. We calculate the resulting inflaton potential and
study the feasibility of the overall tuning given the limited freedom of the
flux landscape. Our preliminary investigations suggest that, even imposing all
tuning conditions, the remaining choice of flux vacua can still be large enough
for such models to provide a promising path to large-field inflation in string
theory.Comment: 46 pages, 6 figures; v2: typos removed, references added; v3:
references adde
Primordial Black Holes from the QCD axion
We propose a mechanism to generate Primordial Black Holes (PBHs) which is
independent of cosmological inflation and occurs slightly below the QCD phase
transition. Our setup relies on the collapse of long-lived string-domain wall
networks and is naturally realized in QCD axion models with domain wall number
and Peccei-Quinn symmetry broken after inflation. In our framework,
dark matter is mostly composed of axions in the meV mass range along with a
small fraction, of
heavy PBHs. The latter could play a role in
alleviating some of the shortcomings of the CDM model on sub-galactic
scales. The scenario has distinct signatures in ongoing axion searches as well
as gravitational wave observatories.Comment: 7 pages, 2 figures. v2: version accepted for publication in PR
Footprints of the QCD Crossover on Cosmological Gravitational Waves at Pulsar Timing Arrays
Pulsar Timing Arrays (PTAs) have reported evidence for a stochastic
gravitational wave (GW) background at nHz frequencies, possibly originating in
the early Universe. We show that the spectral shape of the low-frequency
(causality) tail of GW signals sourced at temperatures around GeV
is distinctively affected by confinement of strong interactions (QCD), due to
the corresponding sharp decrease in the number of relativistic species. A
Bayesian analysis in the latest International PTA dataset reveals a significant
improvement in the fit with respect to cubic power law spectra, previously
employed for the causality tail. Comparison with the results of NANOGrav 15
years and European PTA Data Release 2 suggests that our inclusion of Standard
Model effects on GWs can have a potentially decisive impact on model selection.Comment: 6+9 pages, 7 figure