173 research outputs found
Nambu-Jona-Lasinio Model Coupled to Constant Electromagnetic Fields in D-Dimension
Critical dynamics of the Nambu-Jona-Lasinio model, coupled to a constant
electromagnetic field in D=2, 3, and 4, is reconsidered from a viewpoint of
infrared behavior and vacuum instability. The latter is associated with
constant electric fields and cannot be avoidable in the nonperturbative
framework obtained through the proper time method. As for magnetic fields, an
infrared cut-off is essential to investigate the critical phenomena. The result
reconfirms the fact that the critical coupling in D=3 and 4 goes to zero even
under an infinitesimal magnetic field. There also shows that a non-vanishing
causes instability. A perturbation with
respect to external fields is adopted to investigate critical quantities, but
the resultant asymptotic expansion excellently matches with the exact value.Comment: 27 pages, 17 figure files, LaTe
Holographic Roberge-Weiss Transitions
We investigate N=4 SYM coupled to fundamental flavours at nonzero imaginary
quark chemical potential in the strong coupling and large N limit, using
gauge/gravity duality applied to the D3-D7 system, treating flavours in the
probe approximation. The interplay between Z(N) symmetry and the imaginary
chemical potential yields a series of first-order Roberge-Weiss transitions. An
additional thermal transition separates phases where quarks are bound/unbound
into mesons. This results in a set of Roberge-Weiss endpoints: we establish
that these are triple points, determine the Roberge-Weiss temperature, give the
curvature of the phase boundaries and confirm that the theory is analytic in
mu^2 when mu^2~0.Comment: 37 pages, 13 figures; minor comments added, to appear in JHE
Charges in Gauge Theories
In this article we investigate charged particles in gauge theories. After
reviewing the physical and theoretical problems, a method to construct charged
particles is presented. Explicit solutions are found in the Abelian theory and
a physical interpretation is given. These solutions and our interpretation of
these variables as the true degrees of freedom for charged particles, are then
tested in the perturbative domain and are demonstrated to yield infra-red
finite, on-shell Green's functions at all orders of perturbation theory. The
extension to collinear divergences is studied and it is shown that this method
applies to the case of massless charged particles. The application of these
constructions to the charged sectors of the standard model is reviewed and we
conclude with a discussion of the successes achieved so far in this programme
and a list of open questions.Comment: 47 pages, LaTeX, 14 figures, uses feynmp, necessary Metapost files
included. Review to appear in Pramana, Journal of Physics. Minor LaTeX change
to make page numbers visible on "Letter" paper forma
Holographic rho mesons in an external magnetic field
We study the rho meson in a uniform magnetic field eB using a holographic
QCD-model, more specifically a D4/D8/Dbar8 brane setup in the confinement phase
at zero temperature with two quenched flavours. The parameters of the model are
fixed by matching to corresponding dual field theory parameters at zero
magnetic field. We show that the up- and down-flavour branes respond
differently to the presence of the magnetic field in the dual QCD-like theory,
as expected because of the different electromagnetic charge carried by up- and
down-quark. We discuss how to recover the Landau levels, indicating an
instability of the QCD vacuum at eB = m_rho^2 towards a phase where charged rho
mesons are condensed, as predicted by Chernodub using effective QCD-models. We
improve on these existing effective QCD-model analyses by also taking into
account the chiral magnetic catalysis effect, which tells us that the
constituent quark masses rise with eB. This turns out to increase the value of
the critical magnetic field for the onset of rho meson condensation to eB = 1.1
m_rho^2 = 0.67 GeV^2. We briefly discuss the influence of pions, which turn out
to be irrelevant for the condensation in the approximation made.Comment: 26 pages, 10 .pdf figures, v2: version accepted for publication in
JHE
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
Strongly interacting matter under external magnetic fields within nonlocal NJL-type models
We study the behavior of strongly interacting matter under an external magnetic field in the context of nonlocal NambuâJona-Lasinio (NJL) -like models. We find that at zero temperature the condensates display the well-known Magnetic Catalysis effect, showing a good quantitative agreement with lattice QCD (LQCD) results. Moreover, when extended to finite temperature we find that (contrary to what happens in the local NJL model) the Inverse Magnetic Catalysis (IMC) effect is naturally incorporated. We also analyze the magnetic susceptibility of the QCD vacuum in the limit of small magnetic field, considering two different model parametrizations, and compare our numerical results to those obtained in other theoretical approaches and in LQCD calculations
The Classic: Bone Morphogenetic Protein
This Classic Article is a reprint of the original work by Marshall R. Urist and Basil S. Strates, Bone Morphogenetic Protein. An accompanying biographical sketch of Marshall R. Urist, MD is available at DOI 10.1007/s11999-009-1067-4; a second Classic Article is available at DOI 10.1007/s11999-009-1069-2; and a third Classic Article is available at DOI 10.1007/s11999-009-1070-9. The Classic Article is © 1971 by Sage Publications Inc. Journals and is reprinted with permission from Urist MR, Strates BS. Bone morphogenetic protein. J Dent Res. 1971;50:1392â1406
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