Excess low energy photon pairs from pion annihilation at the chiral phase transition

Волков, М. К.; Kuraev, É. A.; Blaschke, D.; Röpke, G.; Schmidt, S.

doi:10.1016/s0370-2693(98)00227-5

Cited by 44 publications

(29 citation statements)

References 22 publications

(31 reference statements)

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“…(The similar effect in hot hadronic plasma has been considered before [5,6].) They also suggested that the enhancement of the cross section in the reaction πA → π + π − A ′ near 2π threshold reported by the CHAOS collaboration [7], which was originally motivated by a possibility of a strong ππ correlation in matter [8], may be interpreted as an evidence of the partial restoration of chiral symmetry.…”

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confidence: 52%

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In-mediumππcorrelation induced by partial restoration of chiral symmetry

2000

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We show that both the linear and the non-linear chiral models give an enhancement of the ππ cross section near the 2π threshold in the scalar-iso-scalar (I=J=0) channel in nuclear matter. The reduction of the chiral condensate, i.e., the partial chiral restoration in nuclear matter, is responsible for the enhancement in both cases. We extract an effective 4π-nucleon vertex which is responsible for the enhancement but has not been considered in the non-liear models for in-medium ππ interaction. Relation of this vertex and a next-to-leading order terms in the heavy-baryon chiral lagrangian, L (2) πN , is also discussed. 24.85.+p, 14.40.Cs Exploring possible evidence of partial restoration of chiral symmetry in hot and/or dense nuclear medium is an intriguing subject in hadron physics (see e.g., [1,2]). In particular, the softening of the scalar-iso-scalar (I = J = 0) fluctuation in matter could be a distinct signal of the partial restoration of chiral symmetry, as was originally pointed out in [3].In a recent paper [4], Shimizu and two of the present authors have shown, using the linear σ model (LσM), that the partial restoration of chiral symmetry in nuclear matter leads to an enhanced spectral function near the 2π threshold in the σ-channel. (The similar effect in hot hadronic plasma has been considered before [5,6].) They also suggested that the enhancement of the cross section in the reaction πA → π + π − A ′ near 2π threshold reported by the CHAOS collaboration [7], which was originally motivated by a possibility of a strong ππ correlation in matter [8], may be interpreted as an evidence of the partial restoration of chiral symmetry.In fact, the state-of-the-art calculations using the nonlinear chiral lagrangian together with πN many-body dynamics do not reproduce the cross sections in the I = 0 and I = 2 channels simultaneously [9]. In those calculations, the final state interactions of the emitted two pions in nuclei give rise to a slight enhancement of the cross section in the I = 0 channel, but is not sufficient to reproduce the experimental data. This indicates that some additional mechanism such as the partial restoration of chiral symmetry may be relevant for explaining the data. Such effect can be readily incorporated in the LσM as adopted in [4,10], while it is not obvious how to take into account the effect in the non-linear chiral models.The purposes of the present paper are twofold: Firstly, we show that the near-threshold enhancement in the I = J = 0 channel in nuclear matter takes place irrespective of the representations (linear or non-linear) of chiral symmetry, if the effect of partial restoration of chiral symmetry in the medium is properly incorporated. Secondly, we show that L (2) πN , which is a next-to-leading order term in the non-linear chiral lagrangian in the heavy-baryon formalism, gives relevant vertices for the near-threshold enhancement in the I=J=0 channel. Such vertices have not been taken into account in previous calculations of the in-medium ππ scattering in the non-linear...

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confidence: 52%

“…(5,6) takes place in association with partial restoration of chiral symmetry in nuclear matter. In fact, as σ decreases, m * σ approaches 2m π , which implies that T −1 tree (s ≃ 2m π ) tends to be suppressed.…”

Section: 85+p 1440csmentioning

confidence: 99%

In-mediumππcorrelation induced by partial restoration of chiral symmetry

2000

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“…Another point of interest included in the NICA White Paper is the behavior of scalar mesons in the phase diagram [21]. Their properties may trace the chiral restoration transition and provide a potentially observable signal in the twophoton channel [22] if the background can be sufficiently suppressed. Promising progress has also been made by the Functional Renormalization Group approach that provides spectral functions for the quark-meson model phase diagram [23].…”

Section: The Phase Diagram As Probed At Nicamentioning

confidence: 99%

Recent selected theory developments for NICA

Blaschke

2017

EPJ Web Conf.

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Abstract. In this contribution I present a few selected topics of recent theoretical developments of relevance for the NICA facility under construction. In a first part, I discuss new aspects of the QCD phase diagram like the possible existence of a critical endpoint of first-order phase transitions from the perspective of generalizations of the 3-flavor PNJL model including the conjecture of a universal pressure for the onset of deconfinement in heavy-ion collisions and astrophysics. A second part is devoted to first results of the newly constructed event simulator (THESEUS) which is based on the particlization of the former three-fluid hydrodynamics code by Ivanov, Russkikh and Toneev that allows also to study the role of hadronic final state interactions. Possible signals of the mixed phase accessible at NICA are considered. In particular, the robustness of the baryon-stopping signal of deconfinement and the occurrence of antiflow for protons have been investigated for Au+Au collisions in the range of the NICA-MPD energy scan for √ s ∼ 6 . . . 8 GeV. This signal is reflected also in the flow pattern of light nuclear clusters, in particular deuterons. The sharp peak for the K + /π + ratio at √ s ∼ 8 GeV (the "horn" effect) is not obtained in the present version of THESEUS and calls for improvement of the equation of state input. I report the recent progress in developing a generalized Beth-Uhlenbeck approach to a unified description of quark-hadron matter which includes now strangeness and reveals a new mechanism for explaining the K + /π + ratio due to the pronounced occurrence of an anomalous mode in the K + at finite baryochemical potentials.

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“…2) of thermal excitations of the ψ, ⃗ π and σ fields (for details see [35]). Prominent features are (i) degeneracy of m π and m σ at temperatures larger than T pc (µ) or T c (µ), respectively, (ii) a rapid dropping of m ψ at T = T c (µ) and a mild dropping at T ∼ T pc (µ) and (iii) a global minimum of m σ at (T CP , µ CP ) (for the rationale of the softening of the σ -mode, cf., e.g., [36][37][38] and for the impact on di-photon spectra [39,40]). It is remarkable that the mass ordering changes over the T -µ plane, see Fig.…”

Section: Linear σ Modelmentioning

confidence: 99%