Letters in High Energy Physics

The Thermodynamics of Relativistic Multi-Fluid Systems

2020-06-13T13:01:16+00:00

This article extends the single-fluid relativistic irreversible thermodynamics theory of Müller, Israel and
Stewart (hereafter the MIS theory) to a multi-fluid system with inherent species interactions. This is illustrated
in a two-fluid toy-model where an effective complex 4-velocity plays the role of a primary dynamical
parameter. We find that an observer who resides in the real-part of this universe will notice that their
knowledge of the universe parametrized using real, rather than imaginary, quantities are insufficient to fully
determine properties such as the total energy density, pressure or entropy, In fact, such an observer will
deduce the existence of some negative energy that affects the expansion of their perceived real universe.

Applying New Physics to the Problems of the \(\eta′\to\pi^0\gamma\gamma\) Decay

2020-06-13T12:59:01+00:00

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 \(\eta' \to\pi^0\gamma\gamma\). 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, \(\eta' \to\eta\gamma\gamma\), showing that the impact of the hypothetical Dark Photon may be also present in these decays.

Effects of an H-μ-τ coupling in quarkonium lepton flavor violation decays

2020-06-30T00:37:29+00:00

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 f₀ and μ where the experimental limit could strongly improved with the new B factories as Belle II.