High Energy Physics - Phenomenology

Chang, Hao-Ran

doi: 10.1103/physrevd.110.016022pmid: N/A

Abstract: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.

Unal, Caner;Kovetz, Ely D.;Patil, Subodh P.

doi: 10.1103/physrevd.103.063519pmid: N/A

Abstract:Next generation cosmic microwave background spectral distortion and pulsar timing array experiments have the potential to probe primordial fluctuations at small scales with remarkable sensitivity. We demonstrate the potential of these probes to either detect signatures of primordial black holes (PBHs) sourced from primordial overdensities within the standard thermal history of the universe over a 13-decade mass range ${\cal O}(0.1-10^{12})M_\odot$, or constrain their existence to a negligible abundance. Our conclusions are based only on global cosmological signals, and are robust under changes in i) the statistical properties of the primordial density fluctuations (whether Gaussian or non-Gaussian), ii) the merger and accretion history of the PBHs and assumptions about associated astrophysical processes, and iii) clustering statistics. Any positive detection of enhanced primordial fluctuations at small scales would have far-reaching implications from the content of dark matter to origin of BHs in the centers of galaxies, and to the field content of the inflation. On the other hand, their non-detection would also have important corollaries. For example, non-detection up to forecast sensitivities would tell us that PBHs larger than a fraction of a solar mass can constitute no more than a negligible fraction of dark matter. Moreover, non-detection will also rule out the scenario that PBHs generated by primordial overdensities could be the progenitors of super-massive black holes (SMBHs), of topical interest as there are only a few widely accepted proposals for the formation of SMBHs, an even more pressing question after the detection of active galactic nuclei over a billion solar masses at redshifts $z \geq 7$. Finally, non-detection sets the strongest bounds on the amplitude of small scale inflationary fluctuations for over 6 decades.