59 research outputs found
The Inflaton Portal to Dark Matter
We consider the possibility that the inflaton is part of the dark sector and
interacts with the standard model through a portal interaction with a heavy
complex scalar field in equilibrium with the standard model at high energies.
The inflaton and dark matter are encapsulated in a single complex field and
both scalar sectors are charged under different (approximate) global U(1)'s
such that the dark matter, as well as the visible pseudo-scalar are taken to be
relatively light, as pseudo Nambu-Goldstone bosons of the theory. The dark
matter relic density is populated by Freeze-In productions through the inflaton
portal. In particular, after the reheating, production of dark matter by
inflaton decay is naturally suppressed thanks to Planck stringent constraints
on the dark quartic coupling, therefore preserving the non thermal scenario
from any initial condition tuning.Comment: 11 pages, 5 figures, citations added, typos corrected, comments adde
Supergravity, complex parameters and the Janis-Newman algorithm
The Demia\'nski-Janis-Newman algorithm is an original solution generating
technique. For a long time it has been limited to producing rotating solutions,
restricting to the case of a metric and real scalar fields, despite the fact
that Demia\'nski extended it to include more parameters such as a NUT charge.
Recently two independent prescriptions have been given for extending the
algorithm to gauge fields and thus electrically charged configurations. In this
paper we aim to end setting up the algorithm by providing a missing but
important piece, which is how the transformation is applied to complex scalar
fields. We illustrate our proposal through several examples taken from N=2
supergravity, including the stationary BPS solutions from Behrndt et al. and
Sen's axion-dilaton rotating black hole. Moreover we discuss solutions that
include pairs of complex parameters, such as the mass and the NUT charge, or
the electric and magnetic charges, and we explain how to perform the algorithm
in this context (with the example of Kerr-Newman-Taub-NUT and dyonic
Kerr-Newman black holes). The final formulation of the DJN algorithm can
possibly handle solutions with five of the six Pleba\'nski-Demia\'nski
parameters along with any type of bosonic fields with spin less than two
(exemplified with the SWIP solutions). This provides all the necessary tools
for applications to general matter-coupled gravity and to (gauged)
supergravity.Comment: 18 page
The Inflaton Portal to a Highly decoupled EeV Dark Matter Particle
We explore the possibility that the dark-matter relic abundance is generated
in a context where the inflaton is the only mediator between the visible and
the hidden sectors of our universe. Due to the relatively large mass of the
inflaton field, such a portal leads to an extremely feeble interaction between
the dark and the visible sectors suggesting that the dark sector cannot reach
any thermal equilibrium with the visible sector. After the two sectors are
populated by the decay of the inflaton, a heavy dark-matter particle thermally
decouples within the dark sector. Later, a lighter dark particle, whose decay
width is naturally suppressed by the inflaton propagator, decays into the
visible sector after it dominates the energy density of universe. This process
dilutes the dark-matter relic density by injecting entropy in the visible
sector. We show that an inflaton mass of GeV together
with couplings of order one are fully compatible with a dark-matter relic
abundance . As a general feature of the model, the entropy
dilution mechanism is accompanied by a period of early matter domination, which
modifies the amount of e-folds of inflation necessary to accommodate Planck
data. Moreover, the coupling of the inflaton to the dark and visible sectors
brings loop contributions to the inflationary potential which can destabilize
the inflation trajectory. Considering all these complementary constraints, we
show that, in the context of a plateau-inflation scenario such as the
-attractor model, the inflaton can constitute a viable mediator between
the visible sector and a EeV dark-matter candidate. Furthermore, we
show that improved constraints on the tensor-to-scalar ratio and spectral index
could potentially rule out dark-matter scenarios of this sort in the future.Comment: 18 pages, 6 figures, new version after publicatio
Five-dimensional Janis-Newman algorithm
The Janis-Newman algorithm has been shown to be successful in finding new
sta- tionary solutions of four-dimensional gravity. Attempts for a
generalization to higher dimensions have already been found for the restricted
cases with only one angular mo- mentum. In this paper we propose an extension
of this algorithm to five dimensions with two angular momenta - using the
prescription of G. Giampieri - through two specific examples, that are the
Myers-Perry and BMPV black holes. We also discuss possible enlargements of our
prescriptions to other dimensions and maximal number of angular momenta, and
show how dimensions higher than six appear to be much more challenging to treat
within this framework. Nonetheless this general algorithm provides a
unification of the formulation in d = 3, 4, 5 of the Janis-Newman algorithm,
from which which expose several examples including the BTZ black hole.Comment: 27 page
Dark matter and observable Lepton Flavour Violation
Seesaw models with leptonic symmetries allow right-handed (RH) neutrino
masses at the electroweak scale, or even lower, at the same time having large
Yukawa couplings with the Standard Model leptons, thus yielding observable
effects at current or near-future lepton-flavour-violation (LFV) experiments.
These models have been previously considered also in connection to low-scale
leptogenesis, but the combination of observable LFV and successful leptogenesis
has appeared to be difficult to achieve unless the leptonic symmetry is
embedded into a larger one. In this paper, instead, we follow a different route
and consider a possible connection between large LFV rates and Dark Matter
(DM). We present a model in which the same leptonic symmetry responsible for
the large Yukawa couplings guarantees the stability of the DM candidate,
identified as the lightest of the RH neutrinos. The spontaneous breaking of
this symmetry, caused by a Majoron-like field, also provides a mechanism to
produce the observed relic density via the decays of the latter. The
phenomenological implications of the model are discussed, finding that large
LFV rates, observable in the near-future conversion experiments,
require the DM mass to be in the keV range. Moreover, the active-neutrino
coupling to the Majoron-like scalar field could be probed in future detections
of supernova neutrino bursts.Comment: 10 pages, 8 figures; extended discussion, version to appear in PR
Supernova Constraints on Massive (Pseudo)Scalar Coupling to Neutrinos
In this paper we derive constraints on the emission of a massive
(pseudo)scalar from annihilation of neutrinos in the core of supernovae
through the dimension-4 coupling , as well as the effective
dimension-5 operator . While most of earlier
studies have focused on massless or ultralight scalars, our analysis involves
scalar with masses of order which can be copiously produced
during the explosion of supernovae, whose core temperature is generally of
order MeV. From the luminosity and deleptonization
arguments regarding the observation of SN1987A, we exclude a large range of
couplings for the
dimension-4 case, depending on the neutrino flavours involved and the scalar
mass. In the case of dimension-5 operator, for a scalar mass from MeV to 100
MeV the coupling get constrained from to ,
with the cutoff scale explicitly set TeV. We finally show that if
the neutrino burst of a nearby supernova explosion is detected by
Super-Kamiokande and IceCube, the constraints will be largely reinforced.Comment: 17 pages, 4 figures, version to appear in JCA
Generating X-ray lines from annihilating dark matter
We propose different scenarios where a keV dark matter annihilates to produce
a monochromatic signal. The process is generated through the exchange of a
light scalar of mass of order 300 keV - 50 MeV coupling to photon through loops
or higher dimensional operators. For natural values of the couplings and
scales, the model can generate a gamma-ray line which can fit with the recently
identified 3.5 keV X-ray line.Comment: 10 pages, 8 figure
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