We analyze the evolution of a homogenous and pressureless ball of dust (or “star”) in ghost-free massive gravity on de Sitter spacetime. We find that gravitational collapse does not take place for all parameters of the massive gravity theory. For parameters where it does occur, we find the expression for the location of the apparent horizon where it crosses the surface of the star, indicating the location of the apparent horizon of the vacuum solution at that moment. We determine the Ricci curvature at the boundary of the star and extract the finite correction to the curvature of the apparent horizon due to the graviton mass. Finally, we argue that our collapsing solutions cannot be matched to a static, spherically symmetric vacuum solution at the star’s surface, providing further evidence that physical black hole solutions in massive gravity are likely time-dependent.

United States

Roman Berens

Luke Krauth

Rachel A. Rosen

Gravitational collapse in massive gravity in de Sitter spacetime

Random coincidences of nuclear events can be one of the main background sources in low-temperature calorimetric experiments looking for neutrinoless double-beta decay, especially in those searches based on scintillating bolometers embedding the promising double-beta candidate 100 Â Mo, because of the relatively short half-life of the two-neutrino double-beta decay of this nucleus. We show in this work that randomly coinciding events of the two-neutrino double-beta decay of 100 Â Mo in enriched Li 2100MoO4 detectors can be effectively discriminated by pulse-shape analysis in the light channel if the scintillating bolometer is provided with a NeganovâLuke light detector, which can improve the signal-to-noise ratio by a large factor, assumed here at the level of â¼750 on the basis of preliminary experimental results obtained with these devices. The achieved pile-up rejection efficiency results in a very low contribution, of the order of â¼6Ã10-5 Â counts/(keV Â· kg Â· y), to the background counting rate in the region of interest for a large volume ( â¼90 Â cm 3 ) Li 2100MoO4 detector. This background level is very encouraging in view of a possible use of the Li 2100MoO4 solution for a bolometric tonne-scale next-generation experiment as that proposed in the CUPID project.

Ukraine

Japan

D.M. Chernyak

F.A. Danevich

France

L. Dumoulin

Italy

A. Giuliani

Germany

M. Mancuso

P. de Marcillac

S. Marnieros

C. Nones

E. Olivieri

D.V. Poda

V.I. Tretyak

Rejection of randomly coinciding events in Li 2100MoO4 scintillating bolometers using light detectors based on the Neganov–Luke effect

Next generation calorimetric experiments for the search of rare events rely on the detection of tiny amounts of light (of the order of 20 optical photons) to discriminate and reduce background sources and improve sensitivity. Calorimetric detectors are the simplest solution for photon detection at cryogenic (mK) temperatures. The development of silicon based light detectors with enhanced performance thanks to the use of the Neganov–Luke effect is described. The aim of this research line is the production of high performance detectors with industrial-grade reproducibility and reliability.