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Neutral meson properties under an external magnetic field in nonlocal chiral quark models

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 Added by Daniel Gomez Dumm
 Publication date 2017
  fields
and research's language is English




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We study the behavior of neutral meson properties in the presence of a static uniform external magnetic field in the context of nonlocal chiral quark models. The formalism is worked out introducing Ritus transforms of Dirac fields, which allow to obtain closed analytical expressions for $pi^0$ and $sigma$ meson masses and for the $pi^0$ decay constant. Numerical results for these observables are quoted for various parameterizations. In particular, the behavior of the $pi^0$ meson mass with the magnetic field is found to be in good agreement with lattice QCD results. It is also seen that the Goldberger-Treiman and Gell-Mann-Oakes-Renner chiral relations remain valid within these models in the presence of the external magnetic field.



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A detailed study of the analytic structure of 1-loop self energy graphs for neutral and charged $rho$ mesons is presented at finite temperature and arbitrary magnetic field using the real time formalism of thermal field theory. The imaginary part of the self energy is obtained from the discontinuities of these graphs across the Unitary and Landau cuts, which is seen to be different for $rho^0$ and $rho^pm$. The magnetic field dependent vacuum contribution to the real part of the self energy, which is usually ignored, is found to be appreciable. A significant effect of temperature and magnetic field is seen in the self energy, spectral function, effective mass and dispersion relation of $rho^0$ as well as of $rho^pm$ relative to its trivial Landau shift. However, for charged $rho$ mesons, on account of the dominance of the Landau term, the effective mass appears to be independent of temperature. The trivial coupling of magnetic moment of $rho^pm$ with external magnetic field, when incorporated in the calculation, makes the $rho^pm$ to condense at high magnetic field.
We investigate inhomogeneous chiral condensates, such as the so-called dual chiral density wave of dense quark matter, under an external magnetic field at finite real and imaginary chemical potentials. In a model-independent manner, we find that analytic continuation from imaginary to real chemical potential is not possible due to the singularity induced by inhomogeneous chiral condensates at zero chemical potential. From the discussion on the non-analyticity and methods used in lattice QCD simulations, e.g., Taylor expansion, and the analytic continuation with an imaginary chemical potential, it turns out that information on an inhomogeneous chiral condensed phase is missed in the lattice simulations at finite baryon chemical potentials unless the non-analyticity at zero chemical potential is correctly considered. We also discuss an exceptional case without such non-analyticity at zero chemical potential.
We study the behavior of strongly interacting matter under a strong external magnetic field in the context of chiral quark models that include nonlocal interactions. In particular, we analyze the influence of a constant magnetic field on the chiral quark condensates at zero and finite temperature, studying the deconfinement and chiral restoration critical temperatures and discussing the observed magnetic catalysis and inverse magnetic catalysis effects. In addition, we analyze in this framework the behavior of the $pi^0$ mass and decay constant. The predictions of nonlocal chiral quark models are compared with results obtained in lattice QCD.
134 - L. Levkova , C. DeTar 2013
Using numerical simulations of lattice QCD we calculate the effect of an external magnetic field on the equation of state of the quark-gluon plasma. The results are obtained using a Taylor expansion of the pressure with respect to the magnetic field for the first time. The coefficients of the expansion are computed to second order in the magnetic field. Our setup for the external magnetic field avoids complications arising from toroidal boundary conditions, making a Taylor series expansion straightforward. This study is exploratory and is meant to serve as a proof of principle.
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