19 research outputs found

### The neutrino ground state in a neutron star

We address a recent claim that the stability of neutron stars implies a lower
bound on the mass of the neutrino. We argue that the result obtained by some
previous authors is due to an improper summation of an infrared-sensitive
series and that a non-perturbative "resummation" of the series yields a finite
and well-behaved result. The stability of neutron stars thus gives no lower
bound on the mass of the neutrino.Comment: 5 pages, 3 figures, Latex (uses espcrc2.sty); contribution to the
proceedings of Neutrino 98, Takayama, Japan, 4-9 June, 199

### Sum Rules in the CFL Phase of QCD at finite density

We study the asymmetry between the vector current and axial-vector current
correlators in the colour-flavour locking (CFL) phase of QCD at finite density.
Using Weinberg's sum rules, we compute the decay constant $f_\pi$ of the
Goldstone modes and find agreement with previous derivations. Using Das's sum
rule, we also estimate the contribution of electromagnetic interactions to the
mass of the charged modes. Finally, we comment on low temperature corrections
to the effective field theory describing the Goldstone bosons.Comment: 13 pages, revtex, using epsfig. Typo in reference correcte

### Electroweak Symmetry Breaking induced by Dark Matter

The mechanism behind Electroweak Symmetry Breaking (EWSB) and the nature of
dark matter (DM) are currently among the most important issues in high energy
physics. Since a natural dark matter candidate is a weakly interacting massive
particle or WIMP, with mass around the electroweak scale, it is clearly of
interest to investigate the possibility that DM and EWSB are closely related.
In the context of a very simple extension of the Standard Model, the Inert
Doublet Model, we show that dark matter could play a crucial role in the
breaking of the electroweak symmetry. In this model, dark matter is the
lightest component of an inert scalar doublet. The coupling of the latter with
the Standard Model Higgs doublet breaks the electroweak symmetry at one-loop,
"a la Coleman-Weinberg". The abundance of dark matter, the breaking of the
electroweak symmetry and the constraints from electroweak precision
measurements can all be accommodated by imposing an (exact or approximate)
custodial symmetry.Comment: 4 pages, no figure, one tabl

### Varying alpha and black hole entropy

Recently it has been suggested that an increase in the fine structure
constant alpha with time would decrease the entropy of a Reissner-Nordstrom
black hole, thereby violating the second law of thermodynamics. In this note we
point out that, at least for a certain class of charged dilaton black holes
related to string theory, the entropy does not change under adiabatic
variations of alpha and one might expect it to increase for non-adiabatic
changes.Comment: 5 pages, matches version accepted in JHE

### The Inert Doublet Model and Inelastic Dark Matter

The annual modulation observed by DAMA/NaI and DAMA/Libra may be interpreted
in terms of elastic or inelastic scattering of dark matter particles. In this
paper we confront these two scenarios within the framework of a very simple
extension of the Standard Model, the Inert Doublet Model (IDM). In this model
the dark matter candidate is a scalar, the lightest component of an extra Higgs
doublet. We first revisit the case for the elastic scattering of a light scalar
WIMP, M_DM~10 GeV, a scenario which requires that a fraction of events in DAMA
are channelled. Second we consider the possibility of inelastic Dark Matter
(iDM). This option is technically natural in the IDM, in the sense that the
mass splitting between the lightest and next-to-lightest neutral scalars may be
protected by a Peccei-Quinn (PQ) symmetry. We show that candidates with a mass
M_DM between ~535 GeV and ~50 TeV may reproduce the DAMA data and have a cosmic
abundance in agreement with WMAP. This range may be extended to candidates as
light as ~50 GeV if we exploit the possibility that the approximate PQ symmetry
is effectively conserved and that a primordial asymmetry in the dark sector may
survive until freeze-out.Comment: 16 pages, 7 figures. v2: minor changes and discussion on the
embedding in SO(10) added. v3: matches the published version in JCA

### Inflation from a Tachyon Fluid?

Motivated by recent works of Sen and Gibbons, we study the evolution of a
flat and homogeneous universe dominated by tachyon matter. In particular, we
analyse the necessary conditions for inflation in the early roll of a single
tachyon field.Comment: 12 pages, 2 figures, minor corrections and comments on reheating
adde

### Complementarity of Galactic radio and collider data in constraining WIMP dark matter models

In this work we confront dark matter models to constraints that may be
derived from radio synchrotron radiation from the Galaxy, taking into account
the astrophysical uncertainties and we compare these to bounds set by
accelerator and complementary indirect dark matter searches. Specifically we
apply our analysis to three popular particle physics models. First, a generic
effective operator approach, in which case we set bounds on the corresponding
mass scale, and then, two specific UV completions, the Z' and Higgs portals. We
show that for many candidates, the radio synchrotron limits are competitive
with the other searches, and could even give the strongest constraints (as of
today) with some reasonable assumptions regarding the astrophysical
uncertainties.Comment: 22 pages, 12 figure

### Positrons and antiprotons from inert doublet model dark matter

In the framework of the Inert Doublet Model, a very simple extension of the
Standard Model, we study the production and propagation of antimatter in cosmic
rays coming from annihilation of a scalar dark matter particle. We consider
three benchmark candidates, all consistent with the WMAP cosmic abundance and
existing direct detection experiments, and confront the predictions of the
model with the recent PAMELA, ATIC and HESS data. For a light candidate, M_{DM}
= 10 GeV, we argue that the positron and anti-proton fluxes may be large, but
still consistent with expected backgrounds, unless there is an enhancement
(boost factor) in the local density of dark matter. There is also a substantial
anti-deuteron flux which might be observable by future experiments. For a
candidate with M_{DM} = 70 GeV, the contribution to positron and anti-proton
fluxes is much smaller than the expected backgrounds. Even if a boost factor is
invoked to enhance the signals, the candidate is unable to explain the observed
positron and anti-proton excesses. Finally, for a heavy candidate, M_{DM} = 10
TeV, it is possible to fit the PAMELA excess (but, unfortunately, not the ATIC
one) provided there is a large enhancement, either in the local density of dark
matter or through the Sommerfeld effect.Comment: 17 pages ; v2: matches JCAP published versio

### Forays into the dark side of the swamp

International audienceMotivated by the swampland conjectures, we study the cosmological signatures of a quintessence potential which induces time variation in the low-energy effective field theory. After deriving the evolution of the quintessence field, we illustrate its possible ramifications by exploring putative imprints in a number of directions of particle phenomenology. We first show that a dark matter self-interaction rate increasing with time gives a novel way of reconciling the large self-interactions required to address small-scale structure issues with the constraint coming from clusters. Next, we study the effects of kinetic mixing variation during the radiation-dominated era on freeze-in dark matter production. Last, we elucidate quintessence effects on the restoration of the electroweak symmetry at finite temperature and the lifetime of the electroweak vacuum through a modification of the effective Higgs mass and quartic coupling