50 research outputs found
Properties of neutral mesons in a hot and magnetized quark matter
The properties of non-interacting and mesons are studied
at finite temperature, chemical potential and in the presence of a constant
magnetic field. To do this, the energy dispersion relations of these particles,
including nontrivial form factors, are derived using a derivative expansion of
the effective action of a two-flavor, hot and magnetized Nambu--Jona-Lasinio
(NJL) model up to second order. The temperature dependence of the pole and
screening masses as well as the directional refraction indices of magnetized
neutral mesons are explored for fixed magnetic fields and chemical potentials.
It is shown that, because of the explicit breaking of the Lorentz invariance by
the magnetic field, the refraction index and the screening mass of neutral
mesons exhibit a certain anisotropy in the transverse and longitudinal
directions with respect to the direction of the external magnetic field. In
contrast to their longitudinal refraction indices, the transverse indices of
the neutral mesons are larger than unity.Comment: V1: 26 pages, 15 figures; V2: Discussions improved, references added.
Version accepted for publication in PR
Chiral perturbation theory in a magnetic background - finite-temperature effects
We consider chiral perturbation theory for SU(2) at finite temperature in
a constant magnetic background . We compute the thermal mass of the pions
and the pion decay constant to leading order in chiral perturbation theory in
the presence of the magnetic field. The magnetic field gives rise to a
splitting between and as well as between
and . We also calculate the free energy and the
quark condensate to next-to-leading order in chiral perturbation theory. Both
the pion decay constants and the quark condensate are decreasing slower as a
function of temperature as compared to the case with vanishing magnetic field.
The latter result suggests that the critical temperature for the chiral
transition is larger in the presence of a constant magnetic field. The increase
of as a function of is in agreement with most model calculations but
in disagreement with recent lattice calculations.Comment: 24 pages and 9 fig
Inverse magnetic catalysis in field theory and gauge-gravity duality
We investigate the surface of the chiral phase transition in the
three-dimensional parameter space of temperature, baryon chemical potential and
magnetic field in two different approaches, the field-theoretical
Nambu-Jona-Lasinio (NJL) model and the holographic Sakai-Sugimoto model. The
latter is a top-down approach to a gravity dual of QCD with an asymptotically
large number of colors and becomes, in a certain limit, dual to an NJL-like
model. Our main observation is that, at nonzero chemical potential, a magnetic
field can restore chiral symmetry, in apparent contrast to the phenomenon of
magnetic catalysis. This "inverse magnetic catalysis" occurs in the
Sakai-Sugimoto model and, for sufficiently large coupling, in the NJL model and
is related to the physics of the lowest Landau level. While in most parts our
discussion is a pedagogical review of previously published results, we include
new analytical results for the NJL approach and a thorough comparison of
inverse magnetic catalysis in the two approaches.Comment: 37 pages, 11 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Ye
Lattice QCD Simulations in External Background Fields
We discuss recent results and future prospects regarding the investigation,
by lattice simulations, of the non-perturbative properties of QCD and of its
phase diagram in presence of magnetic or chromomagnetic background fields.
After a brief introduction to the formulation of lattice QCD in presence of
external fields, we focus on studies regarding the effects of external fields
on chiral symmetry breaking, on its restoration at finite temperature and on
deconfinement. We conclude with a few comments regarding the effects of
electromagnetic background fields on gluodynamics.Comment: 31 pages, 10 figures, minor changes and references added. To appear
in Lect. Notes Phys. "Strongly interacting matter in magnetic fields"
(Springer), edited by D. Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Ye
Magnetic Catalysis: A Review
We give an overview of the magnetic catalysis phenomenon. In the framework of
quantum field theory, magnetic catalysis is broadly defined as an enhancement
of dynamical symmetry breaking by an external magnetic field. We start from a
brief discussion of spontaneous symmetry breaking and the role of a magnetic
field in its a dynamics. This is followed by a detailed presentation of the
essential features of the phenomenon. In particular, we emphasize that the
dimensional reduction plays a profound role in the pairing dynamics in a
magnetic field. Using the general nature of underlying physics and its
robustness with respect to interaction types and model content, we argue that
magnetic catalysis is a universal and model-independent phenomenon. In support
of this claim, we show how magnetic catalysis is realized in various models
with short-range and long-range interactions. We argue that the general nature
of the phenomenon implies a wide range of potential applications: from certain
types of solid state systems to models in cosmology, particle and nuclear
physics. We finish the review with general remarks about magnetic catalysis and
an outlook for future research.Comment: 37 pages, to appear in Lect. Notes Phys. "Strongly interacting matter
in magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Yee. Version 2: references adde