7,604 research outputs found
Radiation of an electric charge in the field of a magnetic monopole
We consider the radiation of photons from quarks scattering on color-magnetic
monopoles in the Quark-Gluon Plasma. We consider a temperature regime
T\gsim2T_c, where monopoles can be considered as static, rare objects
embedded into matter consisting mostly of the usual "electric" quasiparticles,
quarks and gluons. The calculation is performed in the classical,
non-relativistic approximation and results are compared to photon emission from
Coulomb scattering of quarks, known to provide a significant contribution to
the photon emission rates from QGP. The present study is a first step towards
understanding whether this scattering process can give a sizeable contribution
to dilepton production in heavy-ion collisions. Our results are encouraging: by
comparing the magnitudes of the photon emission rate for the two processes, we
find a dominance in the case of quark-monopole scattering. Our results display
strong sensitivity to finite densities of quarks and monopoles.Comment: 28 pages, 8 figure
The role of monopoles in a Gluon Plasma
We study the role of magnetic monopoles at high enough temperature ,
when they can be considered heavy, rare objects embedded into matter consisting
mostly of the usual "electric" quasiparticles, quarks and gluons. We review
available lattice results on monopoles at finite temperatures. Then we proceed
to classical and quantum charge-monopole scattering, solving the problem of
gluon-monopole scattering for the first time. We find that, while this process
hardly influences thermodynamic quantities, it does produce a large transport
cross section, significantly exceeding that for pQCD gluon-gluon scattering up
to quite high . Thus, in spite of their relatively small density at high
, monopoles are extremely important for QGP transport properties, keeping
viscosity small enough for hydrodynamics to work at LHC.Comment: 60 pages, 15 Figure
On the Reconstruction of Cavities in a Nonlinear Model Arising from Cardiac Electrophysiology
In this paper, we deal with the problem of determining perfectly insulating regions (cavities) from one boundary measurement in a nonlinear elliptic equation arising from cardiac electrophysiology. Based on the results obtained in [9] we propose a new reconstruction algorithm based on Gamma-convergence. The relevance and applicability of this approach are then shown through several numerical experiments
MAPS in 130 nm triple well CMOS technology for HEP applications
Deep N-well CMOS monolithic active pixel sensors (DNWMAPS) represent an alternative approach to signal processing in pixellated detectors for high energy physics experiments. Based on different resolution constraints, two prototype MAPS, suitable for applications requiring different detector pitch, have been developed and fabricated in 130 nm triple well CMOS technology. This work presents experimental results from the characterization of some test structures together with TCAD and Monte Carlo simulations intended to study the device properties in terms of charge diffusion and charge sharing among pixels
Thermodynamics of the PNJL model
QCD thermodynamics is investigated by means of the Polyakov-loop-extended
Nambu Jona-Lasinio (PNJL) model, in which quarks couple simultaneously to the
chiral condensate and to a background temporal gauge field representing
Polyakov loop dynamics. The behaviour of the Polyakov loop as a function of
temperature is obtained by minimizing the thermodynamic potential of the
system. A Taylor series expansion of the pressure is performed. Pressure
difference and quark number density are then evaluated up to sixth order in
quark chemical potential, and compared to the corresponding lattice data. The
validity of the Taylor expansion is discussed within our model, through a
comparison between the full results and the truncated ones.Comment: 6 pages, 5 figures, Talk given at the Workshop for Young Scientists
on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (Hot Quarks
2006), Villasimius, Italy, 15-20 May 200
Polyakov Loop and Gluon Quasiparticles in Yang-Mills Thermodynamics
We study the interpretation of Lattice data about the thermodynamics of the
deconfinement phase of SU(3) Yang-Mills theory, in terms of gluon
quasiparticles propagating in a background of a Polyakov loop. A potential for
the Polyakov loop, inspired by the strong coupling expansion of the QCD action,
is introduced; the Polyakov loop is coupled to tranverse gluon quasiparticles
by means of a gas-like effective potential. This study is useful to identify
the effective degrees of freedom propagating in the gluon medium above the
critical temperature. A main general finding is that a dominant part of the
phase transition dynamics is accounted for by the Polyakov loop dynamics, hence
the thermodynamics can be described without the need for diverging or
exponentially increasing quasiparticle masses as , at
variance respect to standard quasiparticle models.Comment: 8 pages, 9 figure
Debye mass and heavy quark potential in a PNJL quark plasma
We calculate the Debye mass for the screening of the heavy quark potential in
a plasma of massless quarks coupled to the temporal gluon background governed
by the Polyakov loop potential within the PNJL model in RPA approximation. We
give a physical motivation for a recent phenomenological fit of lattice data by
applying the calculated Debye mass with its suppression in the confined phase
due to the Polyakov-loop to a description of the temperature dependence of the
singlet free energy for QCD with a heavy quark pair at infinite separation. We
compare the result to lattice data.Comment: 6 pages, 1 figure, contribution to Proceedings of the 6th
International Conference on "Critical Point and Onset of Deconfinement", to
appear in Phys. At. Nucl., vol. 7
On the harmonics of the low-frequency quasi-periodic oscillation in GRS 1915+105
GRS 1915+105 is a widely studied black hole binary, well known because of its
extremely fast and complex variability. Flaring periods of high variability
alternate with "stable" phases (the plateaux) when the flux is low, the spectra
are hard and the timing properties of the source are similar to those of a
number of black hole candidates in hard spectral state. In the plateaux the
power density spectra are dominated by a low frequency quasi periodic
oscillation (LFQPO) superposed onto a band limited noise continuum and
accompanied by at least one harmonic. In this paper we focus on three plateaux,
presenting the analysis of the power density spectra and in particular of the
LFQPO and its harmonics. While plotting the LFQPO and all the harmonics
together on a frequency-width plane, we found the presence of a positive trend
of broadening when the frequency increases. This trend can shed light in the
nature of the harmonic content of the LFQPO and challenges the usual
interpretation of these timing features.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
Fast and Sensitive Detection of Soil-Borne Cereal Mosaic Virus in Leaf Crude Extract of Durum Wheat
Soil-borne cereal mosaic virus (SBCMV) is a furovirus with rigid rod-shaped particles containing an ssRNA genome, transmitted by Polymyxa graminis Led., a plasmodiophorid that can persist in soil for up to 20 years. SBCMV was reported on common and durum wheat and it can cause yield losses of up to 70%. Detection protocols currently available are costly and time-consuming (real-time PCR) or have limited sensitivity (ELISA). To facilitate an efficient investigation of the real dispersal of SBCMV, it is necessary to develop a new detection tool with the following characteristics: no extraction steps, very fast results, and high sensitivity to allow pooling of a large number of samples. In the present work, we have developed a reverse transcription loop-mediated isothermal amplification (RT-LAMP) protocol with such characteristics, and we have compared it with real-time PCR. Our results show that the sensitivity of LAMP and real-time PCR on cDNA and RT-LAMP on crude extracts are comparable, with the obvious advantage that RT-LAMP produces results in minutes rather than hours. This paves the way for extensive field surveys, leading to a better knowledge of the impact of this virus on wheat health and yield
Multiwavelength campaign on Mrk 509. I. Variability and spectral energy distribution
(Abridged) Active galactic nuclei show a wealth of interesting physical
processes, some of which are poorly understood. We want to address a number of
open questions, including the location and physics of the outflow from AGN, the
nature of the continuum emission, the geometry and physical state of the X-ray
broad emission line region, the Fe-K line complex, the metal abundances of the
nucleus and finally the interstellar medium of our own Galaxy. We study one of
the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a
multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra,
HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our
observations cover more than five decades in frequency, from 2 um to 200 keV.
The combination of high-resolution spectroscopy and time variability allows us
to disentangle and study the different components. Our campaign covers 100 days
from September to December 2009, and is centred on a simultaneous set of deep
XMM-Newton and INTEGRAL observations with regular time intervals, spanning
seven weeks. We obtain a continuous light curve in the X-ray and UV band,
showing a strong, up to 60% flux increase in the soft X-ray band during the
three weeks in the middle of our deepest monitoring campaign, and which is
correlated with an enhancement of the UV flux. This allows us to study the time
evolution of the continuum and the outflow. By stacking the observations, we
have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy
ever obtained. In this paper we also study the effects of the spectral energy
distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks
to our broad-band coverage, uncertainties on the SED do not strongly affect the
determination of this equilibrium.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysic
- …