Abnormal dilepton yield from parity breaking in dense nuclear matter

Kolevatov

Soldati

2011

J. High Energ. Phys.

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Abstract:The problem of propagation of photons and massive vector mesons in the presence of Lorenz and CPT invariance violating medium is studied when the parity-odd medium is bounded by a hyperplane separating it from the vacuum. The solutions in both half-spaces are carefully discussed and in the case of space-like boundary stitched on the boundary with help of the Bogolubov transformations provided by the space-like ChernSimons vector. The presence of two different Fock vacua is shown and the probability amplitude for transmission of particles from vacuum to parity breaking medium is calculated. We have also found classical solutions and showed that the results are consistent with ones obtained by canonical quantization formalism. In the cases, both of entrance to and of escaping from parity-odd medium, the probabilities for reflecting and passing through were found for each polarization using the classical solutions. Finally, the propagator for each polarization is obtained in the momentum space. Boundary effects under consideration are of certain importance for registration of local parity violation in the finite volume of heavy ion fireball and/or of a star with cold axion condensate.

Section: Discussionmentioning

confidence: 99%

Section: Vector Fields In a Pseudoscalar Backgroundmentioning

confidence: 99%

Section: Introduction: Possible Physics Of Time-or Space-dependent Psmentioning

confidence: 99%

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Propagation of photons and massive vector mesons between a parity breaking medium and vacuum

Kolevatov

Soldati

2011

J. High Energ. Phys.

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“…It is justified when using consistently Eqs. (17), (49) and the condition (76) in the SPB phase. Then one obtains the differential equations on functions σ j (μ), ρ(μ), following the same strategy as for (81),…”

Section: Second Variations Of Effective Potential In the Spbmentioning

confidence: 99%

“…It was also shown [75][76][77][78][79] that the associated axial chemical potential causes a distortion of the energy spectrum of photons and vector particles (ρ and ω mesons) due to the Chern-Simons term that is generated. In addition scalar and pseudoscalar mesons get a momentum dependent effective mass [80,81].…”

Section: Introductionmentioning

confidence: 99%

Spontaneous parity violation under extreme conditions: an effective lagrangian analysis

Espriu

2014

Eur. Phys. J. C

We investigate how large baryon densities (and possibly high temperatures) may induce spontaneous parity violation in the composite meson sector of vector-like gauge theory (presumably QCD or techni-QCD). The analysis at intermediate energy scales is done by using an extended σ -model lagrangian that includes two scalar and two pseudoscalar multiplets and fulfills low-energy constraints for vector-like gauge theories. We elaborate on a novel mechanism of parity breaking based on the interplay between lightest and heavier meson condensates, which therefore cannot be realized in the simplest σ model. The results are relevant for idealized homogeneous and infinite nuclear (quark or techniquark) matter where the influence of the density can be examined with the help of a constant chemical potential. The model is able to describe satisfactorily the firstorder phase transition to stable nuclear matter, and it predicts a second-order phase transition to a state where parity is spontaneously broken. We argue that the parity breaking phenomenon is quite generic when a large enough chemical potential is present. Current quark masses are explicitly taken into account in this work and shown not to change the general conclusions.

Abnormal enhancement of dilepton yield in central heavy-ion collisions from local parity breaking

Espriu

et al. 2012

Theor Math Phys

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We propose a novel explanation for the dilepton excess observed in heavy ion collisions at invariant masses below 1 GeV. We argue that the presence of local parity breaking due to a time-dependent isosinglet and/or isotriplet pseudoscalar condensate substantially modifies the dispersion relation of photons and vector mesons propagating in such a medium, changing the ρ spectral function and resulting in a potentially large excess of e + e − and µ + µ − with respect to the theoretical predictions based in a 'cocktail' of known hadronic processes. Possible signatures to prove or disprove this effect are discussed.PACS numbers: 25.75.Cj, 21.65.Jk, 12.40.Vv During the last decade several experiments in heavy ion collisions have indicated an abnormal yield of lepton pairs with invariant mass M < 1 GeV in the region of small rapidities and moderate transversal momenta [1,2] (reviewed in [3,4]). This effect is visible only for collisions that are central or semi-central, and is present for e + e − and also for µ + µ − . From a comparison to pp and p-nucleus collisions it has been established beyond doubt that such an enhancement is a nuclear medium effect [3]. experiments) the abnormal dilepton yield has not been yet explained satisfactorily by known processes in hadronic physics [3,4]. Following [2] we divide the range of dilepton invariant masses into high ( M > 3.2 GeV), low ( M < 1.2 GeV) and intermediate. The low mass region (LMR) is in turn divided into LMR I with M < 0.3 GeV and LMR II with 0.3 GeV < M < 1.2 GeV. In LMR I the enhancement could possibly be explained by modifications of meson properties in nuclear medium [6][7][8][9] as well as by protonneutron scattering [5]. But in the LMR II the ρ meson, directly via ππ fusion or indirectly through Dalitz processes, largely dominates and the in-medium effects of a dropping mass and/or broadening resonance seem unable to explain the spectacular dilepton enhancement by a 4 to 7 factor, depending on p T and centrality (see [10,11] for recent attempts).In this letter we propose a radically different explanation of this enhancement. We suggest that the effect may be a manifestation of local parity breaking (LPB) in colliding nuclei due to the generation of a pseudoscalar, isos- * Corresponding author. E-mail: andrianov@icc.ub.edu inglet or neutral isotriplet, condensate whose magnitude depends on the dynamics of the collision. It has been suggested that such a background could be due to the topological charge fluctuations leading to the so-called Chiral Magnetic Effect (CME) [12] studied by lattice QCD simulations [13] and seemingly detected in the STAR and PHENIX experiments at RHIC [14], although the issue is far from being settled. It might be also related to pseudoscalar domain walls [15]. However the fact that the observed dilepton excess is almost absent for peripheral collisions (where the CME should be more visible) and maximized in cental collisions makes us believe that it may be due to the ephemeral formation of a bona-fide thermodynamic phase where pa...