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Leonardo G Trombetta - One of the best experts on this subject based on the ideXlab platform.
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Hartree Approximation in curved spacetimes revisited ii the semiclassical einstein equations and de sitter self consistent solutions
Physical Review D, 2014Co-Authors: Diana Lopez Nacir, Francisco D Mazzitelli, Leonardo G TrombettaAbstract:We consider the semiclassical Einstein equations (SEE) in the presence of a quantum scalar field with self-interaction $\ensuremath{\lambda}{\ensuremath{\phi}}^{4}$. Working in the Hartree truncation of the two-particle irreducible effective action, we compute the vacuum expectation value of the energy-momentum tensor of the scalar field, which acts as a source of the SEE. We obtain the renormalized SEE by implementing a consistent renormalization procedure. We apply our results to find self-consistent de Sitter solutions to the SEE in situations with or without spontaneous breaking of the ${Z}_{2}$-symmetry.
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Hartree Approximation in curved spacetimes revisited the effective potential in de sitter spacetime
Physical Review D, 2014Co-Authors: Diana Lopez Nacir, Francisco D Mazzitelli, Leonardo G TrombettaAbstract:We consider a quantum scalar eld with 4 interaction in curved spacetimes. The quantum effects are taken into account nonperturbatively using the Hartree Approximation to the 2PI eective action. Although this Approximation has been considered in many previous works, we reconsider it using a consistent nonperturbative renormalization procedure, which we extend to general curved spacetimes. We obtain the renormalized equations for the mean eld and for the propagator of the uctuations, showing explicitly their independence on the arbitrary scale introduced by the regularization scheme. We apply our results to the particular case of de Sitter spacetime and discuss spontaneous symmetry breaking. The results depend strongly on the renormalization procedure.
Jonathan T Lenaghan - One of the best experts on this subject based on the ideXlab platform.
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chiral symmetry restoration at nonzero temperature in the su 3 r su 3 l linear sigma model
Physical Review D, 2000Co-Authors: Jonathan T Lenaghan, Dirk H Rischke, Jurgen SchaffnerbielichAbstract:We study patterns of chiral symmetry breaking at zero temperature and its subsequent restoration at nonzero temperature within the $\mathrm{SU}{(3)}_{r}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(3)}_{l}$ linear sigma model. Gap equations for the masses of the scalar and pseudoscalar mesons and the non-strange and strange quark condensates are systematically derived in the Hartree Approximation via the Cornwall-Jackiw-Tomboulis formalism. In the chiral limit, the chiral symmetry restoring transition is found to be first order, as predicted by universality arguments. Taking the experimental values for the meson masses, however, the transition is crossover. The absence of the $\mathrm{U}{(1)}_{A}$ anomaly is found to drive this transition closer to being first order. At large temperatures, the mixing angles between octet and singlet states approach ideal flavor mixing.
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Chiral symmetry restoration at nonzero temperature in the SU(3)(r) x SU(3)(l) linear sigma model
Physical Review D, 2000Co-Authors: Jonathan T Lenaghan, Dirk H Rischke, Jürgen Schaffner-bielichAbstract:We study patterns of chiral symmetry breaking at zero temperature and its subsequent restoration at nonzero temperature within the SU(3){sub r}xSU(3){sub l} linear sigma model. Gap equations for the masses of the scalar and pseudoscalar mesons and the non-strange and strange quark condensates are systematically derived in the Hartree Approximation via the Cornwall-Jackiw-Tomboulis formalism. In the chiral limit, the chiral symmetry restoring transition is found to be first order, as predicted by universality arguments. Taking the experimental values for the meson masses, however, the transition is crossover. The absence of the U(1){sub A} anomaly is found to drive this transition closer to being first order. At large temperatures, the mixing angles between octet and singlet states approach ideal flavor mixing.
Diana Lopez Nacir - One of the best experts on this subject based on the ideXlab platform.
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Hartree Approximation in curved spacetimes revisited ii the semiclassical einstein equations and de sitter self consistent solutions
Physical Review D, 2014Co-Authors: Diana Lopez Nacir, Francisco D Mazzitelli, Leonardo G TrombettaAbstract:We consider the semiclassical Einstein equations (SEE) in the presence of a quantum scalar field with self-interaction $\ensuremath{\lambda}{\ensuremath{\phi}}^{4}$. Working in the Hartree truncation of the two-particle irreducible effective action, we compute the vacuum expectation value of the energy-momentum tensor of the scalar field, which acts as a source of the SEE. We obtain the renormalized SEE by implementing a consistent renormalization procedure. We apply our results to find self-consistent de Sitter solutions to the SEE in situations with or without spontaneous breaking of the ${Z}_{2}$-symmetry.
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Hartree Approximation in curved spacetimes revisited the effective potential in de sitter spacetime
Physical Review D, 2014Co-Authors: Diana Lopez Nacir, Francisco D Mazzitelli, Leonardo G TrombettaAbstract:We consider a quantum scalar eld with 4 interaction in curved spacetimes. The quantum effects are taken into account nonperturbatively using the Hartree Approximation to the 2PI eective action. Although this Approximation has been considered in many previous works, we reconsider it using a consistent nonperturbative renormalization procedure, which we extend to general curved spacetimes. We obtain the renormalized equations for the mean eld and for the propagator of the uctuations, showing explicitly their independence on the arbitrary scale introduced by the regularization scheme. We apply our results to the particular case of de Sitter spacetime and discuss spontaneous symmetry breaking. The results depend strongly on the renormalization procedure.
Zsolt Szép - One of the best experts on this subject based on the ideXlab platform.
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Broken phase effective potential in the two-loop Φ -derivable Approximation and nature of the phase transition in a scalar theory
Physical Review D, 2012Co-Authors: Gergely Markó, Urko Reinosa, Zsolt SzépAbstract:We study the phase transition of a real scalar phi^4 theory in the two-loop Phi-derivable Approximation using the imaginary time formalism, extending our previous (analytical) discussion of the Hartree Approximation. We combine Fast Fourier Transform algorithms and accelerated Matsubara sums in order to achieve a high accuracy. Our results confirm and complete earlier ones obtained in the real time formalism [1] but which were less accurate due to the integration in Minkowski space and the discretization of the spectral density function. We also provide a complete and explicit discussion of the renormalization of the two-loop Phi-derivable Approximation at finite temperature, both in the symmetric and in the broken phase, which was already used in the real-time approach, but never published. Our main result is that the two-loop Phi-derivable Approximation suffices to cure the problem of the Hartree Approximation regarding the order of the transition: the transition is of the second order type, as expected on general grounds. The corresponding critical exponents are, however, of the mean-field type. Using a "RG-improved" version of the Approximation, motivated by our renormalization procedure, we find that the exponents are modified. In particular, the exponent delta, which relates the field expectation value phi to an external field h, changes from 3 to 5, getting then closer to its expected value 4.789, obtained from accurate numerical estimates [2].
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Broken phase scalar effective potential and Φ -derivable Approximations
Physical Review D, 2011Co-Authors: Urko Reinosa, Zsolt SzépAbstract:We study the effective potential of a real scalar phi^4 theory as a function of the temperature T within the simplest Phi-derivable Approximation, namely the Hartree Approximation. We apply renormalization at a "high" temperature T* where the theory is required to be in its symmetric phase and study how the effective potential evolves as the temperature is lowered down to T=0. In particular, we prove analytically that no second order phase transition can occur in this particular Approximation of the theory, in agreement with earlier studies based on the numerical evaluation or the high temperature expansion of the effective potential. This work is also an opportunity to illustrate certain issues on the renormalization of Phi-derivable Approximations at finite temperature and non-vanishing field expectation value, and to introduce new computational techniques which might also prove useful when dealing with higher order Approximations.
N. Van Giai - One of the best experts on this subject based on the ideXlab platform.
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Spin symmetry in Dirac negative-energy spectrum in density-dependent relativistic Hartree-Fock theory
European Physical Journal A, 2015Co-Authors: H. Liang, J Meng, W Long, N. Van GiaiAbstract:The spin symmetry in the Dirac negative-energy spectrum and its origin are investigated for the first time within the density-dependent relativistic Hartree-Fock (DDRHF) theory. Taking the nucleus 16O as an example, the spin symmetry in the negative-energy spectrum is found to be a good Approximation and the dominant components of the Dirac wave functions for the spin doublets are nearly identical. In comparison with the relativistic Hartree Approximation where the origin of spin symmetry lies in the equality of the scalar and vector potentials, in DDRHF the cancellation between the Hartree and Fock terms is responsible for the better spin symmetry properties and determines the subtle spin-orbit splitting. These conclusions hold even in the case when significant deviations from the G -parity values of the meson-antinucleon couplings occur.
