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C. Germani

Publications and source records attributed to C. Germani.

5 recordsLinked to original sources
arXiv2019

Physics potential of the International Axion Observatory (IAXO)

We review the physics potential of a next generation search for solar axions: the International Axion Observatory (IAXO). Endowed with a sensitivity to discover axion-like particles (ALPs) with a coupling to photons as small as $g_{a\gamma}\sim 10^{-12}$ GeV$^{-1}$, or to electrons $g_{ae}\sim$10$^{-13}$, IAXO has the potential to find the QCD axion in the 1 meV$\sim$1 eV mass range where it solves the strong CP problem, can account for the cold dark matter of the Universe and be responsible for the anomalous cooling observed in a number of stellar systems. At the same time, IAXO will have enough sensitivity to detect lower mass axions invoked to explain: 1) the origin of the anomalous "transparency" of the Universe to gamma-rays, 2) the observed soft X-ray excess from galaxy clusters or 3) some inflationary models. In addition, we review string theory axions with parameters accessible by IAXO and discuss their potential role in cosmology as Dark Matter and Dark Radiation as well as their connections to the above mentioned conundrums.

hep-ph↗
arXiv2019

Electromagnetic probes of primordial black holes as dark matter

The LIGO discoveries have rekindled suggestions that primordial black holes (BHs) may constitute part to all of the dark matter (DM) in the Universe. Such suggestions came from 1) the observed merger rate of the BHs, 2) their unusual masses, 3) their low/zero spins, and 4) also from the independently uncovered cosmic infrared background (CIB) fluctuations signal of high amplitude and coherence with unresolved cosmic X-ray background (CXB). Here we summarize the prospects to resolve this important issue with electromagnetic observations using the instruments and tools expected in the 2020's. These prospects appear promising to make significant, and potentially critical, advances. We demonstrate that in the next decade, new space- and ground-borne electromagnetic instruments, combined with concurrent theoretical efforts, should shed critical light on the long-considered link between primordial BHs and DM. Specifically the new data and methodologies under this program will involve: I) Probing with high precision the spatial spectrum of source-subtracted CIB with Euclid and WFIRST, and its coherence with unresolved cosmic X-ray background using eROSITA and Athena, II) Advanced searches for microlensing of Galactic stars by the intervening Galactic Halo BHs with OGLE, Gaia, LSST and WFIRST, III) Supernovae (SNe) lensing in the upcoming surveys with WFIRST, LSST and also potentially with Euclid and JWST, IV) Advanced theoretical work to understand the details of PBH accretion and evolution and their influence on cosmic microwave background (CMB) anisotropies in light of the next generation CMB experiments, V) Better new samples and theoretical understanding involving stability and properties of ultra faint dwarf galaxies, pulsar timing, and cosmological quasar lensing.

astro-ph.CO↗
arXiv2005

Gravitational collapse and evolution of holographic black holes

Gravitational collapse is analyzed in the Brane-World by arguing that regularity of five-dimensional geodesics require that stars on the brane have an atmosphere. For the simple case of a spherically symmetric cloud of non-dissipating dust, conditions are found for which the collapsing star evaporates and approaches the Hawking behavior as the (apparent) horizon is being formed. The effective energy of the star vanishes at a finite radius and the star afterwards re-expands and "anti-evaporates". Israel junction conditions across the brane (holographically related to the matter trace anomaly) and the projection of the Weyl tensor on the brane (holographically interpreted as the quantum back-reaction on the brane metric) contribute to the total energy as, respectively, an "anti-evaporation" and an "evaporation" term.

hep-th↗