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Register a new userImpact of a uniform magnetic field and nonzero temperature on explicit chiral symmetry breaking in QED: Arbitrary hierarchy of energy scales
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Employing the Schwingers proper-time method, we calculate the $<bar{psi} psi>$-condensate for massive Dirac fermions of charge $e$ interacting with a uniform magnetic field in a heat bath. We present general results for arbitrary hierarchy of the energy scales involved, namely, the fermion mass $m$, the magnetic field strength $sqrt{eB}$ and temperature $T$. Moreover, we study particular regimes in detail and reproduce some of the results calculated or anticipated earlier in the literature. We also discuss possible applications of our findings.
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Using the nonperturbative Schwinger-Dyson equation, we show that chiral symmetry is dynamically broken in QED at weak couplings when an external magnetic field is present, and that chiral symmetry is restored at temperatures above $T_c simeq alphapi^2/sqrt{2 pi |eH|}$, where $alpha$ is the fine structure constant and $H$ is the magnetic field strength.
The relative contributions of explicit and dynamical chiral symmetry breaking in QCD models of the quark-gap equation are studied in dependence of frequently employed ansatze for the dressed interaction and quark-gluon vertex. The explicit symmetry breaking contributions are defined by a constituent-quark sigma term whereas the combined effects of explicit and dynamical symmetry breaking are described by a Euclidean constituent-mass solution. We extend this study of the gap equation to a quark-gluon vertex beyond the Abelian approximation complemented with numerical gluon- and ghost-dressing functions from lattice QCD. We find that the ratio of the sigma term over the Euclidean mass is largely independent of nonperturbative interaction and vertex models for current-quark masses, $m_{u,d}(mu) leq m(mu) leq m_b(mu)$, and equal contributions of explicit and dynamical chiral symmetry breaking occur at $m(mu) approx 400$~MeV. For massive solutions of the gap equation with lattice propagators this value decreases to about 200~MeV.
We study chiral symmetry breaking in QED when a uniform external magnetic field is present. We calculate higher order corrections to the dynamically generated fermion mass and find them to be small. In so doing we correct an error in the literature regarding the matrix structure of the fermion self-energy.
Inspired by recent discussions of inverse magnetic catalysis in the literature, we examine the effects of a uniform external magnetic field on the chiral phase transition in quenched ladder QED at nonzero chemical potential. In particular, we study the behaviour of the effective potential as the strength of the magnetic field is varied while the chemical potential is held constant. For a certain range of the magnetic field, the effective potential develops a local maximum. Inverse magnetic catalysis is observed at this maximum, whereas the usual magnetic catalysis is observed at the true minimum of the effective potential.
Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge couplings when an external magnetic field is present. In this paper, we show that chiral symmetry is restored above a critical chemical potential and the corresponding phase transition is of first order. In contrast, the chiral symmetry restoration at high temperatures (and at zero chemical potential) is a second order phase transition.
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