Nuclear Theory·nucl-th

Thursday·August 27, 2020

9 papers—6 primary·3 cross-listed

07
[Submitted on 25 Aug 2020] (cross-list from hep-ph)
Can a protophobic vector boson explain the ATOMKI anomaly?
Xilin Zhang🇺🇸 · Gerald A. Miller🇺🇸
In 2016, the ATOMKI collaboration announced [PRL {\bf 116}, 042501 (2016)] observing an unexpected enhancement of the $e^{+} - e^{-}$ pair production signal in one of the $^{8}$ Be nuclear transitions induced by an incident proton beam on a $^{7}$ Li target. Many beyond-standard-model physics explanations have subsequently been proposed. One popular theory is that the anomaly is caused by the creation of a protophobic vector boson ( $X$ ) with a mass around 17 MeV [e.g., PRL\ {\bf 117}, 071803 (2016)] in the nuclear transition. We study this hypothesis by deriving an isospin relation between photon and $X$ couplings to nucleons. This allows us to find simple relations between protophobic $X$ -production cross sections and those for measured photon production. The net result is that $X$ production is dominated by direct transitions induced by $E 1^{X}$ and $L 1^{X}$ (transverse and longitudinal electric dipoles) and $C 1^{X}$ (charge dipole) without going through any nuclear resonance (i.e. Bremsstrahlung radiation) with a smooth energy dependence that occurs for all proton beam energies above threshold. This contradicts the experimental observations and invalidates the protophobic vector boson explanation.
Comments:
8 pages, 4 figures, 1 table. Version close to the published: detailed discussions on multipoles and experimental signal (with a new figure) are included
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2008.11288 [pdf]
PLB(2021)·46 citations
08
[Submitted on 26 Aug 2020] (cross-list from hep-ph)
Reduction for one-loop tensor Feynman integrals in the relativistic quantum field theories at finite temperature and/or finite density
Hao-Ran Chang🇨🇳
The \emph{conventional} Passarino-Veltman reduction is a systematic procedure based on the Lorentz covariance, which can efficiently reduce the one-loop tensor Feynman integrals in the relativistic quantum field theories (QFTs) at zero temperature and zero density. However, the Lorentz covariance is explicitly broken when either of the temperature and density is finite, due to a rest reference frame of the many-body system in which the temperature and density are measured, rendering the \emph{conventional} Passarino-Veltman reduction not applicable anymore to reduce the one-loop tensor Feynman integrals therein. In this paper, we report a \emph{generalized} Passarino-Veltman reduction which can efficiently simplify the one-loop tensor Feynman integrals in the relativistic QFTs at finite temperature and/or finite density. The \emph{generalized} Passarino-Veltman reduction can analyze the one-loop tensor Feynman integrals in a wide range of physical systems described by the relativistic QFTs at finite temperature and/or finite density, such as quark-gluon plasma in nuclear physics.
Comments:
28 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Theory (nucl-th)
arXiv:
2008.11314 [pdf]
PRD(2024)·2 citations
09
[Submitted on 26 Aug 2020] (cross-list from hep-lat)
Sensitivity of the Polyakov loop and related observables to chiral symmetry restoration
David Anthony Clarke🇩🇪 · Olaf Kaczmarek🇨🇳 · Frithjof Karsch🇩🇪 · Anirban Lahiri🇩🇪 · Mugdha Sarkar🇩🇪
While the Polyakov loop is an order parameter of the deconfinement transition in the heavy quark mass regime of QCD, its sensitivity to the deconfinement of light, dynamical quarks in QCD is not apparent. On the other hand, the quark mass dependence of the Polyakov loop is sensitive to the appearance of a chiral phase transition. Using lattice QCD calculations in the staggered fermion discretization scheme at finite values of the lattice spacing, $a T = 1/8$ , we show here, for the first time, that the Polyakov loop expectation value, and the heavy quark free energy extracted from it, behave like energy-like observables in the vicinity of the chiral phase transition temperature $T_{c}$ . Consistent with scaling behavior of energy-like observables in the 3- $d$ , O(2) universality class, the quark mass derivatives diverge in the chiral limit at $T_{c}$ while the temperature derivatives stay finite. The latter will develop a characteristic spike at $T_{c}$ . This, however, may be resolved only in calculations with quark masses being two orders of magnitude smaller than those currently accessible in lattice QCD calculations.
Comments:
6 pages, 3 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2008.11678 [pdf]
PRD(2021)·36 citations

Affiliations

first authorsco-authorsvia INSPIRE

Can a protophobic vector boson explain the ATOMKI anomaly?

Reduction for one-loop tensor Feynman integrals in the relativistic quantum field theories at finite temperature and/or finite density

Sensitivity of the Polyakov loop and related observables to chiral symmetry restoration

Affiliations