13,774 research outputs found
The Semi-Hooperon: Gamma-ray and anti-proton excesses in the Galactic Center
A puzzling excess in gamma-rays at GeV energies has been observed in the
center of our galaxy using Fermi-LAT data. Its origin is still unknown, but it
is well fitted by Weakly Interacting Massive Particles (WIMPs) annihilations
into quarks with a cross section around with masses
of ~GeV, scenario which is promptly revisited. An excess favoring
similar WIMP properties has also been seen in anti-protons with AMS-02 data
potentially coming from the Galactic Center as well. In this work, we explore
the possibility of fitting these excesses in terms of semi-annihilating dark
matter, dubbed as semi-Hooperon, with the process being responsible for the gamma-ray excess, where X=h,Z. An
interesting feature of semi-annihilations is the change in the relic density
prediction compared to the standard case, and the possibility to alleviate
stringent limits stemming from direct detection searches. Moreover, we discuss
which models might give rise to a successful semi-Hooperon setup in the context
of , and extra "dark" gauge symmetries.Comment: 8 pages, 3 figures, version published in Phys. Lett.
Fractional Brownian motions ruled by nonlinear equations
In this note we consider generalized diffusion equations in which the
diffusivity coefficient is not necessarily constant in time, but instead it
solves a nonlinear fractional differential equation involving fractional
Riemann-Liouville time-derivative. Our main contribution is to highlight the
link between these generalised equations and fractional Brownian motion (fBm).
In particular, we investigate the governing equation of fBm and show that its
diffusion coefficient must satisfy an additive evolutive fractional equation.
We derive in a similar way the governing equation of the iterated fractional
Brownian motion.Comment: 7 page
Monetary Policy Rules, Asset Prices and Exchange Rates
We examine empirically whether asset prices and exchange rates may be admitted into a standard interest rate rule, using data for the US, the UK and Japan since 1979. Asset prices and exchange rates can be employed as information variables for a standard ‘Taylor-type’ rule or as arguments in an augmented interest rate rule. Our empirical evidence, based on measures of the output gap proxied by marginal costs calculations, suggests that monetary policy-makers may use asset prices and exchange rates not only as part of their information set for setting interest rates, but also to set interest rates to offset deviations of asset prices or exchange rates from their equilibrium levels. These results are open to several alternative interpretations.Asset prices; exchange rates; interest rate rules; monetary policy.
Does Microcredit Reach the Poor and Vulnerable? Evidence from Northern Bangladesh
Subsidized loans have a history of being diverted to the rich. Yet recently microcredit programs, such as the Grameen Bank in Bangladesh, have become popular among donors and governments as a way to channel funds to the poor. This paper uses a unique panel dataset from two Bangladeshi villages to test if the modern microcredit movement is different from its predecessors. Poverty is measured by levels of consumption. Vulnerability is measured as fluctuations in consumption associated with inefficient risk sharing. We find that subsidized credit is largely successful at reaching the poor and vulnerable. The probability that a microcredit member is below the poverty line is substantially higher than that of a randomly picked household in both villages. In the village where female headed households were found to be vulnerable, nearly half of the female headed households belonged to microcredit programs yet only a quarter of male headed households were microcredit members. While restricting loans to the landless is not effective in reaching the poor and vulnerable, targeting female headed households is.
Pseudoscalar Mediators: A WIMP model at the Neutrino Floor
Due to its highly suppressed cross section (fermionic) dark matter
interacting with the Standard Model via pseudoscalar mediators is expected to
be essentially unobservable in direct detection experiments. We consider both a
simplified model and a more realistic model based on an extended two Higgs
doublet model and compute the leading one-loop contribution to the effective
dark matter- nucleon interaction. This higher order correction dominates the
scattering rate completely and can naturally, i.e. for couplings of order one,
lead to a direct detection cross section in the vicinity of the neutrino floor.
Taking the observed relic density and constraints from low-energy observables
into account we analyze the direct detection prospects in detail and find
regions of parameter space that are within reach of upcoming direct detection
experiments such as XENONnT, LZ, and DARWIN.Comment: 29 pages, 8 figure
A first principle computation of the thermodynamics of glasses
We propose a first principle computation of the equilibrium thermodynamics of
simple fragile glasses starting from the two body interatomic potential. A
replica formulation translates this problem into that of a gas of interacting
molecules, each molecule being built of m atoms, and having a gyration radius
(related to the cage size) which vanishes at zero temperature. We use a small
cage expansion, valid at low temperatures, which allows to compute the cage
size, the specific heat (which follows the Dulong and Petit law), and the
configurational entropy.Comment: Latex, 40 pages, 9 figures, corrected misprints, improved
presentatio
Augury of Darkness: The Low-Mass Dark Z' Portal
Dirac fermion dark matter models with heavy mediators are
subject to stringent constraints from spin-independent direct searches and from
LHC bounds, cornering them to live near the resonance. Such
constraints can be relaxed, however, by turning off the vector coupling to
Standard Model fermions, thus weakening direct detection bounds, or by
resorting to light masses, below the Z pole, to escape heavy
resonance searches at the LHC. In this work we investigate both cases, as well
as the applicability of our findings to Majorana dark matter. We derive
collider bounds for light gauge bosons using the method,
spin-dependent scattering limits, as well as the spin-independent scattering
rate arising from the evolution of couplings between the energy scale of the
mediator mass and the nuclear energy scale, and indirect detection limits. We
show that such scenarios are still rather constrained by data, and that near
resonance they could accommodate the gamma-ray GeV excess in the Galactic
center.Comment: 25 pages, 6 Figures. Typos correcte
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