arXiv subjects

Francesc Ferrer

Publications and source records attributed to Francesc Ferrer.

At least 37 records · Page 2Linked to original sources

arXiv2014

Intergalactic magnetic field spectra from diffuse gamma rays

Non-vanishing parity-odd correlators of gamma ray arrival directions observed by Fermi-LAT indicate the existence of a helical intergalactic magnetic field (Tashiro et al.2013). We successfully test this hypothesis using more stringent cuts of the data, Monte Carlo simulations with Fermi-LAT time exposure information, separate analyses for the northern and southern galactic hemispheres, and confirm predictions made in Tashiro & Vachaspati (2014). With some further technical assumptions, we show how to reconstruct the magnetic helicity spectrum from the parity-odd correlators.

astro-ph.CO↗

arXiv2014

Search for CP Violating Signature of Intergalactic Magnetic Helicity in the Gamma Ray Sky

The existence of a cosmological magnetic field could be revealed by the effects of non-trivial helicity on large scales. We evaluate a CP odd statistic, $Q$, using gamma ray data obtained from Fermi satellite observations at high galactic latitudes to search for such a signature. Observed values of $Q$ are found to be non-zero; the probability of a similar signal in Monte Carlo simulations is $\sim 0.2\%$. Contamination from the Milky Way does not seem to be responsible for the signal since it is present even for data at very high galactic latitudes. Assuming that the signal is indeed due to a helical cosmological magnetic field, our results indicate left-handed magnetic helicity and field strength $\sim 10^{-14}~{\rm G}$ on $\sim 10~{\rm Mpc}$ scales.

astro-ph.CO↗

arXiv2014

The Scientific Reach of Multi-Ton Scale Dark Matter Direct Detection Experiments

The next generation of large scale WIMP direct detection experiments have the potential to go beyond the discovery phase and reveal detailed information about both the particle physics and astrophysics of dark matter. We report here on early results arising from the development of a detailed numerical code modeling the proposed DARWIN detector, involving both liquid argon and xenon targets. We incorporate realistic detector physics, particle physics and astrophysical uncertainties and demonstrate to what extent two targets with similar sensitivities can remove various degeneracies and allow a determination of dark matter cross sections and masses while also probing rough aspects of the dark matter phase space distribution. We find that, even assuming dominance of spin-independent scattering, multi-ton scale experiments still have degeneracies that depend sensitively on the dark matter mass, and on the possibility of isospin violation and inelasticity in interactions. We find that these experiments are best able to discriminate dark matter properties for dark matter masses less than around 200 GeV. In addition, and somewhat surprisingly, the use of two targets gives only a small improvement (aside from the advantage of different systematics associated with any claimed signal) in the ability to pin down dark matter parameters when compared with one target of larger exposure.

astro-ph.CO↗

arXiv2013

The impact of the phase-space density on the indirect detection of dark matter

We study the indirect detection of dark matter when the local dark matter velocity distribution depends upon position, as expected for the Milky Way and its dwarf spheroidal satellites, and the annihilation cross-section is not purely s-wave. Using a phase-space distribution consistent with the dark matter density profile, we present estimates of cosmic and gamma-ray fluxes from dark matter annihilations. The expectations for the indirect detection of dark matter can differ significantly from the usual calculation that assumes that the velocity of the dark matter particles follows a Maxwell-Boltzmann distribution.

astro-ph.HE↗

arXiv2013

Dark matter distributions around massive black holes: A general relativistic analysis

The cold dark matter at the center of a galaxy will be redistributed by the presence of a massive black hole. The redistribution may be determined using an approach pioneered by Gondolo and Silk: begin with a model distribution function for the dark matter, and ``grow'' the black hole adiabatically, holding the adiabatic invariants of the motion constant. Unlike the approach of Gondolo and Silk, which adopted Newtonian theory together with ad hoc correction factors to mimic general relativistic effects, we carry out the calculation fully relativistically, using the exact Schwarzschild geometry of the black hole. We find that the density of dark matter generically vanishes at r=2R_S, not 4R_S as found by Gondolo and Silk, where R_S is the Schwarzschild radius, and that the spike very close to the black hole reaches significantly higher densities. We apply the relativistic adiabatic growth framework to obtain the final dark matter density for both cored and cusped initial distributions. Besides the implications of these results for indirect detection estimates, we show that the gravitational effects of such a dark matter spike are significantly smaller than the relativistic effects of the black hole, including frame dragging and quadrupolar effects, for stars orbiting close to the black hole that might be candidates for testing the black hole no-hair theorems.

astro-ph.GA↗

arXiv2012

Detecting Chameleon Dark Energy via Electrostatic Analogy

The late-time accelerated expansion of the universe could be caused by a scalar field that is screened on small scales, as in chameleon or symmetron scenarios. We present an analogy between thin shell configurations of such scalar fields and electrostatics, which allows calculation of the field profile for general extended bodies. Interestingly, the field demonstrates a `lightning rod' effect, where it becomes enhanced near the ends of a pointy or elongated object. Drawing from this correspondence, we show that non-spherical test bodies immersed in a background field will experience a net torque caused by the scalar field. This effect, with no counterpart in the gravitational case, can be potentially tested in future experiments.

astro-ph.CO↗

arXiv2012

Constraints on Light Hidden Sector Gauge Bosons from Supernova Cooling

We derive new bounds on hidden sector gauge bosons which could produce new energy loss mechanisms in supernovae, enlarging the excluded region in mass-coupling space by a significant factor compared to earlier estimates. Both considerations of trapping and possible decay of these particles need to be incorporated when determining such bounds, as does scattering on both neutrons and protons. For masses and couplings near the region which saturates current bounds, a significant background of such gauge bosons may also be produced due to the cumulative effects of all supernovae over cosmic history.

astro-ph.CO↗

arXiv2010

Degree-scale anomalies in the CMB: localizing the first peak dip to a small patch of the north ecliptic sky

Noticeable deviations from the prediction of the fiducial LCDM cosmology are found in the angular power spectrum of the CMB. Besides large-angle anomalies, the WMAP 1st year data revealed a dip in the power spectrum at l \sim 200, which seemed to disappear in the 3rd year and subsequent angular power spectra. Using the WMAP 1st, 3rd, and 5th year data as well as the 5 year coadded data, we study the intensity and spatial distribution of this feature in order to unveil its origin and its implications for the cosmological parameters. We show that in all WMAP data releases there is a substantial suppression of the first Doppler peak in a region near the north ecliptic pole.

astro-ph.CO↗

arXiv2010

Dark matter in natural supersymmetric extensions of the Standard Model

We explore the dark matter sector in extensions of the Minimal Supersymmetric Standard Model (MSSM) that can provide a good fit to the PAMELA cosmic ray positron excess, while at the same time addressing the little hierarchy problem of the MSSM. Adding a singlet Higgs superfield, S, can account for the observed positron excess, as recently discussed in the literature, but we point out that it requires a fine-tuned choice for the parameters of the model. We find that including an additional singlet allows both a reduction of the weak-scale fine-tuning, and an interpretation of the cosmic ray observations in terms of dark matter annihilations in the galactic halo. Our setup contains a light axion, but does not require light CP-even scalars in the spectrum.

hep-ph↗

arXiv2009

Secular evolution of galaxies and galaxy clusters in decaying dark matter cosmology

If the dark matter sector in the universe is composed by metastable particles, galaxies and galaxy clusters are expected to undergo significant secular evolution from high to low redshift. We show that the decay of dark matter, with a lifetime compatible with cosmological constraints, can be at the origin of the observed evolution of the Tully-Fisher relation of disk galaxies and alleviate the problem of the size-evolution of elliptical galaxies, while being consistent with the current observational constraints on the gas fraction of clusters of galaxies.

astro-ph.CO↗

arXiv2009

Cosmological acceleration from a gas of strings

In string gas cosmology, the extra dimensions of the underlying theory are kept at a microscopic scale by a gas of strings. In the matter-dominated era, however, dust pressure can lead to oscillations of the extra dimensions and to acceleration in the three visible dimensions, even with a vanishing cosmological term. We review the resulting oscillating expansion history, that provides an acceptable fit to the observed accelerated expansion of the Universe.

hep-th↗

arXiv2009

Fitting oscillating string gas cosmology to supernova data

In string gas cosmology, extra dimensions are stabilised by a gas of strings. In the matter-dominated era, competition between matter pushing the extra dimensions to expand and the string gas pulling them back can lead to oscillations of the extra dimensions and acceleration in the visible dimensions. We fit this model to supernova data, taking into account the Big Bang Nucleosynthesis constraint on the energy density of the string gas. The fit to the Union set of supernova data is acceptable, but the fit to the ESSENCE data is poor.

hep-th↗

arXiv2008

Helical Magnetic Fields from Sphaleron Decay and Baryogenesis

Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in these models creates helical cosmic magnetic fields. After a transitory period, electroweak dynamics is found to conserve the Chern-Simons number and the total electromagnetic helicity. We argue that baryogenesis could lead to magnetic fields of nano-Gauss strength today on astrophysical length scales. In addition to being astrophysically relevant, such helical magnetic fields can provide an independent probe of baryogenesis and CP violation in particle physics.

astro-ph↗

arXiv2007

Lovelock inflation and the number of large dimensions

We discuss an inflationary scenario based on Lovelock terms. These higher order curvature terms can lead to inflation when there are more than three spatial dimensions. Inflation will end if the extra dimensions are stabilised, so that at most three dimensions are free to expand. This relates graceful exit to the number of large dimensions.

hep-th↗

arXiv2006

Indirect detection of light neutralino dark matter in the NMSSM

We explore the prospects for indirect detection of neutralino dark matter in supersymmetric models with an extended Higgs sector (NMSSM). We compute, for the first time, one-loop amplitudes for NMSSM neutralino pair annihilation into two photons and two gluons, and point out that extra diagrams (with respect to the MSSM), featuring a potentially light CP-odd Higgs boson exchange, can strongly enhance these radiative modes. Expected signals in neutrino telescopes due to the annihilation of relic neutralinos in the Sun and in the Earth are evaluated, as well as the prospects of detection of a neutralino annihilation signal in space-based gamma-ray, antiproton and positron search experiments, and at low-energy antideuteron searches. We find that in the low mass regime the signals from capture in the Earth are enhanced compared to the MSSM, and that NMSSM neutralinos have a remote possibility of affecting solar dynamics. Also, antimatter experiments are an excellent probe of galactic NMSSM dark matter. We also find enhanced two photon decay modes that make the possibility of the detection of a monochromatic gamma-ray line within the NMSSM more promising than in the MSSM.

hep-ph↗

arXiv2006

Light superconducting strings in the Galaxy

Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 KeV gamma-ray line emission from the bulge, which require an intense source of positrons in the galactic center. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma-ray background. Here we suggest that light superconducting strings could be the source of the observed 511 KeV emission. The associated particle physics, at the ~ 1 TeV scale, is within reach of planned accelerator experiments, while the distinguishing spatial distribution, proportional to the galactic magnetic field, could be mapped by SPI or by future, more sensitive, satellite missions.

astro-ph↗

arXiv2006

Zero modes on cosmic strings in an external magnetic field

A classical analysis suggests that an external magnetic field can cause trajectories of charge carriers on a superconducting domain wall or cosmic string to bend, thus expelling charge carriers with energy above the mass threshold into the bulk. We study this process by solving the Dirac equation for a fermion of mass $m_f$ and charge $e$, in the background of a domain wall and a magnetic field of strength $B$. We find that the modes of the charge carriers get shifted into the bulk, in agreement with classical expectations. However the dispersion relation for the zero modes changes dramatically -- instead of the usual linear dispersion relation, $ω_k =k$, the new dispersion relation is well fit by $ω\approx m_f tanh(k/k_*)$ where $k_*=m_f$ for a thin wall in the weak field limit, and $k_*=eBw$ for a thick wall of width $w$. This result shows that the energy of the charge carriers on the domain wall remains below the threshold for expulsion even in the presence of an external magnetic field. If charge carriers are expelled due to an additional perturbation, they are most likely to be ejected at the threshold energy $\sim m_f$.

hep-th↗

arXiv2006

Dark energy and decompactification in string gas cosmology

We study the stability of extra dimensions in string gas cosmology at late times. Vacuum energy and, interestingly, baryons lead to decompactification after they become dynamically important. The string gas can stabilise the effect of baryons, but not that of vacuum energy. However, we find that the interplay of baryons and strings can lead to acceleration in the visible dimensions, without the need for vacuum energy.

hep-th↗