arXiv subjects

France

Publications and source records attributed to France.

9 recordsLinked to original sources

arXiv2020

High-energy and Very High-energy Constraints from Log-parabolic Spectral Models in Narrow-line Seyfert 1 Galaxies

Narrow-line Seyfert 1 galaxies (NLSy1s) are a well-established class of $\gamma$-ray sources, showing the presence of a jet like the more common flat-spectrum radio quasars. The evidence of $\gamma$-ray emission poses the issue of the location of the $\gamma$-ray emitting zone and of the contribution of the $\gamma$-$\gamma$ absorption within the broad-line region (BLR), since such objects have been detected by Fermi-LAT in the MeV-GeV energy range but not by imaging atmospheric Cherenkov telescopes beyond 100 GeV. We discuss how the spectral properties of three NLSy1s (SBS 0846+513, PMN J0948+0022, and PKS 1502+036) derived from the Fermi Large Area Telescope Fourth Source Catalog (4FGL) compare with theoretical models based on the observed properties of the BLR. In particular, we focus on the question on how simple power-law spectral models and log-parabolic ones could be disentangled in $\gamma$-ray narrow-line Seyfert 1 galaxies by means of current Fermi-LAT or future imaging atmospheric Cherenkov telescopes data. We find that the only possibility for a log-parabolic model to mimic a power-law model in the energy band above $E \sim 100$ GeV is to have a very small value of the curvature parameter $ \beta \sim 0.05$.

astro-ph.HE↗

arXiv2019

Interior potential of a toroidal shell from pole values

We have investigated the toroidal analog of ellipsoidal shells of matter, which are of great significance in Astrophysics. The exact formula for the gravitational potential $\Psi(R,Z)$ of a shell with a circular section at the pole of toroidal coordinates is first established. It depends on the mass of the shell, its main radius and axis-ratio $e$ (i.e. core-to-main radius ratio), and involves the product of the complete elliptic integrals of the first and second kinds. Next, we show that successive partial derivatives $\partial^{n +m} \Psi/\partial_{R^n} \partial_{Z^m}$ are also accessible by analytical means at that singular point, thereby enabling the expansion of the interior potential as a bivariate series. Then, we have generated approximations at orders $0$, $1$, $2$ and $3$, corresponding to increasing accuracy. Numerical experiments confirm the great reliability of the approach, in particular for small-to-moderate axis ratios ($e^2 \lesssim 0.1$ typically). In contrast with the ellipsoidal case (Newton's theorem), the potential is not uniform inside the shell cavity as a consequence of the curvature. We explain how to construct the interior potential of toroidal shells with a thick edge (i.e. tubes), and how a core stratification can be accounted for. This is a new step towards the full description of the gravitating potential and forces of tori and rings. Applications also concern electrically-charged systems, and thus go beyond the context of gravitation.

astro-ph.SR↗

arXiv2019

Updated Summation Model: An Improved Agreement with the Daya Bay Antineutrino Fluxes

A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our Total Absorption Gamma-ray Spectroscopy measurements performed during the last decade. For the first time the spectral measurements from the Daya Bay experiment are compared with the detected antineutrino energy spectrum computed with the updated summation method without any renormalisation. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2 to 5 MeV range, the region which dominates the detected flux. An unexpected systematic trend is found that the detected antineutrino flux computed with the summation model decreases with the inclusion of more Pandemonium free data. The detected flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new Pandemonium free data leaving less and less room to the reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the $^{235}$U, $^{239}$Pu, $^{241}$Pu and $^{238}$U are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.

nucl-ex↗

arXiv2014

NuSTAR Discovery of a cyclotron line in KS 1947+300

We present a spectral analysis of three simultaneous NuSTAR and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broad-band observations were supported by Swift/XRT monitoring snap-shots every 3 days, which we use to study the evolution of the spectrum over the outburst. We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P ~ 18.8 s. The 0.8-79 keV broad-band spectrum can be described by a power-law with an exponential cutoff and a black-body component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B ~ 1.1e12 (1+z)G, which is at the lower end of known cyclotron line sources.

astro-ph.HE↗

arXiv2013

Harmony search to solve the container storage problem with different container types

This paper presents an adaptation of the harmony search algorithm to solve the storage allocation problem for inbound and outbound containers. This problem is studied considering multiple container type (regular, open side, open top, tank, empty and refrigerated) which lets the situation more complicated, as various storage constraints appeared. The objective is to find an optimal container arrangement which respects their departure dates, and minimize the re-handle operations of containers. The performance of the proposed approach is verified comparing to the results generated by genetic algorithm and LIFO algorithm.

cs.AI↗

arXiv1997

The Bloch-Nordsieck propagator at finite temperature

We have shown recently that the resummation of soft photon contributions leads to a non-exponential decay of the fermion excitations in hot QED plasmas. The retarded propagator of a massless fermion was found to behave as $S_R(t >> 1/gT) \sim \exp{-\alpha T t [\ln(\omega_p t) + C]}$, where $\omega_p=gT/3$ is the plasma frequency, $\alpha=g^2/4\pi$, and $C$ is a constant, independent of $g$, which was left undefined. This term is computed in this paper. In gauges with unphysical degrees of freedom, it is gauge-fixing independent provided an infrared regulator is introduced in the gauge sector. We also extend our analysis to hot QCD and express the quark and gluon propagators in the form of three-dimensional Euclidean functional integrals which may be evaluated on the lattice.

hep-ph↗

arXiv1996

The quasiparticle structure of hot gauge theories

The study of the ultrarelativistic plasmas in perturbation theory is plagued with infrared divergences which are not eliminated by the screening corrections. They affect, in particular, the computation of the lifetime of the elementary excitations, thus casting doubt on the validity of the quasiparticle picture. We show that, for Abelian plasmas at least, the infrared problem of the damping rate can be solved by a non-perturbative treatment based on the Bloch-Nordsieck approximation. The resulting expression of the fermion propagator is free of divergences, and exhibits a {\it non-exponential} damping at large times: $S_R(t)\sim \exp\{-αT t \lnω_pt\}$, where $ω_p=gT/3$ is the plasma frequency and $α=g^2/4π$.

hep-ph↗

arXiv1996

Lifetime of quasiparticles in hot gauge theories

The perturbative calculation of the lifetime of charged excitations in ultrarelativistic plasmas is plagued with infrared divergences which are not eliminated by the screening corrections. The physical processes responsible for these divergences are the collisions involving the exchange of longwavelength, quasistatic, magnetic gluons (or photons), which are not screened by plasma effects. In QED, the leading divergences can be resummed in a non-perturbative treatement based on a generalization of the Bloch-Nordsieck model at finite temperature. The resulting expression of the fermion propagator is free of infrared problems, and exhibits a ``non-exponential'' damping at large times: $S_R(t)\sim exp {-αT t lnω_pt}$, where $ω_p=eT/3$ is the plasma frequency and $α=e^2/4π$.

hep-ph↗

arXiv1996

Monopoles in the gauge theory of the t-J model

We consider a RG approach for the plasma of magnetic monopoles of the Ioffe-Larkin approach to the t-J model. We first derive the interaction parameters of the 2+1 plasma of magnetic monopoles. The total charge along the time axis is constrained to be zero for each lattice plaquette. Under the one-plaquette approximation, the problem is equivalent to a one dimensional neutral plasma interacting via a potential $V(t) \sim t^α$, with $α=1/3$. The plasma is in a dipolar phase if $α\ge 1$ and a possibility of transition towards a Debye screening phase arises if $α< 1$, so that there exists a critical Fermi wave vector $k_f^{*}$ such as the plasma is Debye screening if $k_f k_f^{*}$. The 2+1 dimensional problem is treated numerically. We show that $k_f^{*}$ decreases and goes to zero as the number of colors increases. This suggests that the assumption of spin-charge decoupling within the slave-boson scheme is self-consistent at large enough values of $N$ and small enough doping. Elsewhere, a confining force between spinons and antiholons appears, suggesting a transition to a Fermi liquid state.

cond-mat↗