Daniele Teresi

The de Sitter (dS) entropy bound gives the maximal number of e-folds that non-eternal inflation can last before violating the thermodynamical interpretation of dS space. This semiclassical argument is the analogue, for dS space, of the Black-Hole information paradox. We use techniques developed to address the latter, namely the island formula, to calculate semiclassically the fine-grained entropy as seen by a Minkowskian observer after inflation and find that this follows a Page-like curve, never exceeding the thermodynamic dS entropy. This calculation, performed for a CFT in 2D gravity, suggests that the semiclassical expectation should be modified in such a way that the entropy bound might actually not be present.

At colliders massive long-lived charged particles could be revealed through their anomalously large ionisation energy loss dE/dx. In this paper we explore a class of scenarios in which the LLPs are particularly boosted, owing to production from the decay of a heavy parent resonance. Such scenarios give rise to unique signatures as compared to traditionally considered dE/dx new-physics benchmarks. We demonstrate that this class of models, unlike traditional new-physics theories, can explain the recently reported excess of events in the dE/dx search by the ATLAS collaboration without conflicting with the determination of β from ionisation and time-of-flight measurements.

We present a cosmological solution to the electroweak hierarchy problem. After discussing general features of cosmological approaches to naturalness, we extend the Standard Model with two light scalars very weakly coupled to the Higgs and present the mechanism, which we recently introduced in a companion paper to explain jointly the electroweak hierarchy and the strong-CP problem. In this work we show that this solution can be decoupled from the strong-CP problem and discuss its possible implementations and phenomenology. The mechanism works with any standard inflationary sector, it does not require weak-scale inflation or a large number of e-folds, and does not introduce ambiguities related to eternal inflation. The cutoff of the theory can be as large as the Planck scale, both for the Cosmological Constant and for the Higgs sector. Reproducing the observed dark matter relic density fixes the couplings of the two new scalars to the Standard Model, offering a target to future axion or fifth force searches. Depending on the specific interaction of the scalars with the Standard Model, the mechanism either yields rich phenomenology at colliders or provides a novel joint solution to the strong-CP problem. We highlight what predictions are common to most realizations of cosmological selection of the weak scale and will allow to test this general framework in the near future.

First order phase transitions can leave relic pockets of false vacua and their particles, that manifest as macroscopic Dark Matter. We compute one predictive model: a gauge theory with a dark quark relic heavier than the confinement scale. During the first order phase transition to confinement, dark quarks remain in the false vacuum and get compressed, forming Fermi balls that can undergo gravitational collapse to stable dark dwarfs (bound states analogous to white dwarfs) near the Chandrasekhar limit, or primordial black holes.

Local minima of the potential can be metastable up to cosmologically long times thanks to energy conservation. We explore the possibility that theories with negative kinetic energy (ghosts) can be metastable up to cosmologically long times. In classical mechanics, ghosts undergo spontaneous lockdown rather than run away if weakly coupled and nonresonant. Physical examples of this phenomenon are shown. In quantum mechanics, this leads to metastability similar to vacuum decay. In classical field theory, lockdown is broken by resonances and ghosts behave statistically, drifting toward infinite entropy as no thermal equilibrium exists. We analytically and numerically compute the runaway rate finding that it is cosmologically slow in four-derivative gravity, where ghosts have gravitational interactions only. In quantum field theory, the ghost runaway rate is naively infinite in perturbation theory, analogously to what is found in early attempts to compute vacuum tunnelling; we do not know the true rate.

We consider an ultralight scalar coupled to the Higgs in the presence of heavier new physics. In the electroweak broken phase the Higgs gives a tree-level contribution to the light-scalar potential, while new physics contributes at loop level. Thereby, the theory has a cosmologically metastable phase where the light scalar is around the top of its potential, and the Higgs is a loop factor lighter than new physics. Such regions with precarious naturalness are anthropically and environmentally selected, as regions with heavier Higgs crunch quickly. We expect observable effects of rolling in the dark-energy equation of state. Furthermore, vacuum energies up to the weak scale can be canceled down to anthropically small values.