Letters in High Energy Physics 2020-06-30T00:37:29+00:00 Professor Shaaban Khalil Open Journal Systems The Thermodynamics of Relativistic Multi-Fluid Systems 2020-06-13T13:01:16+00:00 Bob Osano <p>This article extends the single-fluid relativistic irreversible thermodynamics theory of Müller, Israel and<br>Stewart (hereafter the MIS theory) to a multi-fluid system with inherent species interactions. This is illustrated<br>in a two-fluid toy-model where an effective complex 4-velocity plays the role of a primary dynamical<br>parameter. We find that an observer who resides in the real-part of this universe will notice that their<br>knowledge of the universe parametrized using real, rather than imaginary, quantities are insufficient to fully<br>determine properties such as the total energy density, pressure or entropy, In fact, such an observer will<br>deduce the existence of some negative energy that affects the expansion of their perceived real universe.</p> 2020-04-01T17:16:01+00:00 ##submission.copyrightStatement## Applying New Physics to the Problems of the \(\eta′\to\pi^0\gamma\gamma\) Decay 2020-06-13T12:59:01+00:00 Yaroslav Balytskyi <p>Rare decays of light mesons may be a discovery window for a new weakly coupled forces hidden at a low-energy QCD scale. BES-III Collaboration reported an observation of the rare decay \(\eta'&nbsp;\to\pi^0\gamma\gamma\). The observed decay width disagrees with the preliminary theoretical estimates. We show that this tension may be attributed to New Physics, presumably Dark Photon. For completeness, we consider a possible influence of New Physics on a similar well-measured decay \(\eta \to\pi^0\gamma\gamma\) and a recently measured one, \(\eta'&nbsp;\to\eta\gamma\gamma\), showing that the impact of the hypothetical Dark Photon may be also present in these decays.</p> 2020-05-26T23:46:08+00:00 ##submission.copyrightStatement## Effects of an H-μ-τ coupling in quarkonium lepton flavor violation decays 2020-06-30T00:37:29+00:00 David Delepine Mauro Napsuciale Eduardo Peinado <p>In this work we study the consistency of a possible non-vanishing coupling Hμτ smaller than 0.25% as pointed by the CMS collaborations [1], with measured lepton flavor violation processes involving quarkonium. We show that the most promising channel to confirm this excess is to look for the lepton flavor tau decay into a f<sub>0</sub> and μ where the experimental limit could strongly improved with the new B factories as Belle II.</p> 2020-06-19T07:01:09+00:00 ##submission.copyrightStatement##