494 research outputs found
Chiral transition in a magnetic field and at finite baryon density
We consider the quark-meson model with two quark flavors in a constant
external magnetic field at finite temperature and finite baryon
chemical potential . We calculate the full renormalized effective
potential to one-loop order in perturbation theory. We study the system in the
large- limit, where we treat the bosonic modes at tree level. It is shown
that the system exhibits dynamical chiral symmetry breaking, i. e. that an
arbitrarily weak magnetic field breaks chiral symmetry dynamically, in
agreement with earlier calculations using the NJL model. We study the influence
on the phase transition of the fermionic vacuum fluctuations. For strong
magnetic fields, and in the chiral limit, the transition
is first order in the entire plane if vacuum fluctuations are not
included and second order if they are included. At the physical point, the
transition is a crossover for with and without vacuum fluctuations.Comment: 11 pages. 5figs. V2: fixed a few typos and added refs. Submitted to
PRD. V3: Added refs and substantial revision of tex
SXP 7.92: A Recently Rediscovered Be/X-ray Binary in the Small Magellanic Cloud, Viewed Edge On
We present a detailed optical and X-ray study of the 2013 outburst of the Small Magellanic Cloud Be/X-ray binary SXP 7.92, as well as an overview of the last 18 years of observations from OGLE (Optical Gravitational Lensing Experiment), RXTE, Chandra and XMM-Newton. We revise the position of this source to RA(J2000) = 00:57:58.4, Dec(J2000) = â72:22:29.5 with a 1Ï uncertainty of 1.5 arcsec, correcting the previously reported position by Coe et al. by more than 20 arcmin. We identify and spectrally classify the correct counterpart as a B1Ve star. The optical spectrum is distinguished by an uncharacteristically deep narrow Balmer series, with the Hα line in particular having a distinctive shell profile, i.e. a deep absorption core embedded in an emission line. We interpret this as evidence that we are viewing the system edge on and are seeing self-obscuration of the circumstellar disc. We derive an optical period for the system of 40.0 ±â0.3 d, which we interpret as the orbital period, and present several mechanisms to describe the X-ray/optical behaviour in the recent outburst, in particular the âflares'and âdipsâ seen in the optical light curve, including a transient accretion disc and an elongated precessing disc
Low-energy theorems of QCD and bulk viscosity at finite temperature and baryon density in a magnetic field
The nonperturbative QCD vacuum at finite temperature and a finite baryon
density in an external magnetic field is studied. Equations relating
nonperturbative condensates to the thermodynamic pressure for , and are obtained, and low-energy theorems are derived. A bulk
viscosity is expressed in terms of basic thermodynamical
quantities describing the quark-gluon matter at , , and
. Various limiting cases are also considered.Comment: 12 pages; v2: title changed, new section about bulk viscosity and new
references added; v3: new discussion adde
Expressive generalized itemsets
Generalized itemset mining is a powerful tool to discover multiple-level correlations among the analyzed data. A taxonomy is used to aggregate data items into higher-level concepts and to discover frequent recurrences among data items at different granularity levels. However, since traditional high-level itemsets may also represent the knowledge covered by their lower-level frequent descendant itemsets, the expressiveness of high-level itemsets can be rather limited. To overcome this issue, this article proposes two novel itemset types, called Expressive Generalized Itemset (EGI) and Maximal Expressive Generalized Itemset (Max-EGI), in which the frequency of occurrence of a high-level itemset is evaluated only on the portion of data not yet covered by any of its frequent descendants. Specifically, EGI s represent, at a high level of abstraction, the knowledge associated with sets of infrequent itemsets, while Max-EGIs compactly represent all the infrequent descendants of a generalized itemset. Furthermore, we also propose an algorithm to discover Max-EGIs at the top of the traditionally mined itemsets. Experiments, performed on both real and synthetic datasets, demonstrate the effectiveness, efficiency, and scalability of the proposed approac
Gauge-invariant quark-antiquark nonlocal condensates in lattice QCD
We study, by numerical simulations on a lattice, the behaviour of the
gauge-invariant quark-antiquark nonlocal condensates in the QCD vacuum with
dynamical fermions. A determination is also done in the quenched approximation
and the results are compared with the full-QCD case. The fermionic correlation
length is extracted and compared with the analogous gluonic quantity.Comment: 14 pages, LaTeX file, + 6 PS figure
Dynamical Symmetry Breaking in Models with the Yukawa Interaction
We discuss models with a massless fermion and a self-interacting massive
scalar field with the Yukawa interaction. The chiral condensate and the fermion
mass are calculated analytically. It is shown that the models have a phase
transition as a function of the squared mass of the scalar field.Comment: 7 pages, no figures, in Eqs. (7) and (11) one coefficient was change
04/18/1997 - Collective Soul To Perform At EIU.pdf
International audienceâș We present a spectroscopic method to discriminate biotic from abiotic carbonates. âș Infrared spectral modifications induced by thermal processing are investigated. âș We analyse carbonate samples with no evidences of biomineralization. âș Our method is a powerful tool for the search of life on Mars
Present Status of Lattice QCD at nonzero T and \mu
I review a few selected topics in Lattice Quantum Chromo Dynamics, focusing
more on the recent results. These include i) the equation of state and speed of
sound, ii) J/\psi suppression, iii) flavour correlations and iv) the QCD phase
diagram in the \mu-T plane.Comment: 13 Pages including figures, Plenary Talk at the 9th Workshop on High
Energy Physics Phenomenology, ``WHEPP9'', Bhubaneswar, India, January 3-14,
2006, To appear in Praman
Pressure and non-linear susceptibilities in QCD at finite chemical potentials
When the free energy density of QCD is expanded in a series in the chemical
potential, mu, the Taylor coefficients are the non-linear quark number
susceptibilities. We show that these depend on the prescription for putting
chemical potential on the lattice, making all extrapolations in chemical
potential prescription dependent at finite lattice spacing. To put bounds on
the prescription dependence, we investigate the magnitude of the non-linear
susceptibilities over a range of temperature, T, in QCD with two degenerate
flavours of light dynamical quarks at lattice spacing 1/4T. The prescription
dependence is removed in quenched QCD through a continuum extrapolation, and
the dependence of the pressure, P, on mu is obtained.Comment: 15 pages, 2 figures. Data on chi_uuuu added, discussion enhance
Pion Form Factor in the NLC QCD SR approach
We present results of a calculation of the electromagnetic pion form factor
within a framework of QCD Sum Rules with nonlocal condensates and using a
perturbative spectral density which includes \mathcal{O}(\alpha_s)
contributions.Comment: 9 pages, 2 figures (embedded). Talk presented by the second author at
the Workshop on Physics of Fundamental Interactions, Institute of High Energy
Physics, Protvino, Russia, 22--25 December 200
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