Vincenzo Vitagliano

Horizon thermodynamics and spacetime mappings

When black holes are dynamical, event horizons are replaced by apparent and trapping horizons. Conformal and Kerr-Schild transformations are widely used in relation with dynamical black holes and we study the behaviour under such transformations of quantities related to the thermodynamics of these horizons, such as the Misner-Sharp-Hernandez mass (internal energy), the Kodama vector, surface gravity, and temperature. The transformation properties are not those expected on the basis of naive arguments.

Raychaudhuri equation in spacetimes with torsion

The Authors wish to thank Jose P. S. Lemos for early discussions on a first version of the paper. We thank FCT-Portugal for financial support through Project No. PEst-OE/FIS/UI0099/2015. PL thanks IDPASC and FCT-Portugal for financial support through Grant No. PD/BD/114074/2015. VV is supported by the FCTPortugal grant SFRH/BPD/77678/2011.

Hawking–Hayward quasi-local energy under conformal transformations

We derive a formula describing the transformation of the Hawking-Hayward quasi-local energy under a conformal rescaling of the spacetime metric. A known formula for the transformation of the Misner-Sharp-Hernandez mass is recovered as a special case.

Covariantly quantum Galileon

We derive the 1-loop effective action of the cubic Galileon coupled to quantum-gravitational fluctuations in a background and gauge-independent manner, employing the covariant framework of DeWitt and Vilkovisky. Although the bare action respects shift symmetry, the coupling to gravity induces an effective mass to the scalar, of the order of the cosmological constant, as a direct result of the non-flat field-space metric, the latter ensuring the field-reparametrization invariance of the formalism. Within a gauge-invariant regularization scheme, we discover novel, gravitationally induced non-Galileon higher-derivative interactions in the effective action. These terms, previously unnoticed within standard, non-covariant frameworks, are not Planck suppressed. Unless tuned to be sub-dominant, their presence could have important implications for the classical and quantum phenomenology of the theory.

Geometrically Induced Magnetic Catalysis and Critical Dimensions

We discuss the combined effect of magnetic fields and geometry in interacting fermionic systems. At leading order in the heat-kernel expansion, the infrared singularity (that in flat space leads to the magnetic catalysis) is regulated by the chiral gap effect, and the catalysis is deactivated by the effect of the scalar curvature. We discover that an infrared singularity is found in higher-order terms that mix the magnetic field with curvature, and these lead to a novel form of geometrically induced magnetic catalysis. The dynamical mass squared is then modified not only due to the chiral gap effect by an amount proportional to the curvature, but also by a magnetic shift ∝(4-D)eB, where D represents the number of space-time dimensions. We argue that D=4 is a critical dimension across which the behavior of the magnetic shift changes qualitatively.

Apparent horizons in Clifton-Mota-Barrow inhomogeneous universe

VINCENZO VITAGLIANO, VALERIO FARAONI, THOMAS P. SOTIRIOU and STEFANO LIBERATI 1 CENTRA, Departamento de Fisica, Instituto Superior Tecnico, Universidade Tecnica de Lisboa UTL, Av. Rovisco Pais 1, 1049 Lisboa, Portugal 2 Physics Department and STAR Research Cluster, Bishop’s University, Sherbrooke, Quebec, Canada J1M 1Z7 3 SISSA, Via Bonomea 265, 34136 Trieste, Italy and INFN, Sezione di Trieste, Italy

HIGH-Z COSMOGRAPHY AT A GLANCE

Cosmography is the tool that makes possible to untie the interpretation of cosmological observations from the definition of any dynamical prior. We review the constraints on the cosmographic parameter obtained using the most thorough data set ensemble available. We focus on some specific topics about the statistically based selection of the most stringent fitting expansion.

Cosmography with high-redshift probes

I discuss how the cosmographic approach to the determination of cosmological parameters can be implemented with the inclusion of high-redshift data. I argue on the viability of such high- z probes for cosmographic purposes, and resume some statistical issues in finding the most reliable cosmographic truncation.