Jose L. F. Barbon

On the Naturalness of Higgs inflation

We critically examine the recent claim that the standard model (SM) Higgs boson H could drive inflation in agreement with observations if |H|{sup 2} has a strong coupling {xi}{approx}10{sup 4} to the Ricci curvature scalar. We first show that the effective-theory approach upon which that claim is based ceases to be valid beyond a cutoff scale {lambda}=m{sub p}/{xi}, where m{sub p} is the reduced Planck mass. We then argue that knowing the Higgs potential profile for the field values relevant for inflation (|H|>m{sub p}/{radical}({xi})>>{lambda}) requires knowledge of the ultraviolet completion of the SM beyond {lambda}. In absence of such microscopic theory, the extrapolation of the pure SM potential beyond {lambda} is unwarranted and the scenario is akin to other ad hoc inflaton potentials afflicted with significant fine-tuning. The appealing naturalness of this minimal proposal is therefore lost.

Holographic entanglement entropy probes (non)locality

We study the short-distance structure of geometric entanglement entropy in certain theories with a built-in scale of nonlocality. In particular we examine the cases of Little String Theory and Noncommutative Yang-Mills theory, using their AdS/CFT descriptions. We compute the entanglement entropy via the holographic ansatz of Ryu and Takayanagi to conclude that the area law is violated at distance scales that sample the nonlocality of these models, being replaced by an extensive volume law. In the case of the noncommutative model, the critical length scale that reveals the area/volume law transition is strongly affected by UV/IR mixing effects. We also present an argument showing that Lorentz symmetry tends to protect the area law for theories with field-theoretical density of states.

AdS crunches, CFT falls and cosmological complementarity

We discuss aspects of the holographic description of crunching AdS cosmologies. We argue that crunching FRW models with hyperbolic spatial sections are dual to semiclassical condensates in deformed de Sitter CFTs. De Sitter-invariant condensates with a sharply defined energy scale are induced by effective negative-definite relevant or marginal operators, which may or may not destabilize the CFT. We find this result by explicitly constructing a ‘complementarity map’ for this model, given by a conformal transformation of the de Sitter CFT into a static time-frame, which reveals the crunch as an infinite potential-energy fall in finite time. We show that, quite generically, the crunch is associated to a finite mass black hole if the de Sitter O(d, 1)-invariance is an accidental IR symmetry, broken down to U(1) × O(d) in the UV. Any such regularization cuts off the eternity of de Sitter space-time. Equivalently, the dimension of the Hilbert space propagating into the crunch is finite only when de Sitter is not eternal.

Holography of AdS vacuum bubbles

We consider the fate of AdS vacua connected by tunneling events. A precise holographic dual of thin-walled Coleman-de Luccia bounces is proposed in terms of Fubini instantons in an unstable CFT. This proposal is backed by several qualitative and quantitative checks, including the precise calculation of the instanton action appearing in evaluating the decay rate. Big crunches manifest themselves as time dependent processes which reach the boundary of field space in a finite time. The infinite energy difference involved is identified on the boundary and highlights the ill-defined nature of the bulk setup. We propose a qualitative scenario in which the crunch is resolved by stabilizing the CFT, so that all attempts at crunching always end up shielded from the boundary by the formation of black hole horizons. In all these well defined bulk processes the configurations have the same asymptotics and are finite energy excitations.

Chaotic Fast Scrambling At Black Holes

Fast scramblers process information in characteristic times scaling logarithmically with the entropy, a behavior which has been conjectured for black hole horizons. In this note we use the AdS/CFT fold to argue that causality bounds on information flow only depend on the properties of a single thermal cell, and admit a geometrical interpretation in terms of the optical depth, i.e. the thickness of the Rindler region in the so-called optical metric. The spatial sections of the optical metric are well approximated by constant-curvature hyperboloids. We use this fact to propose an effective kinetic model of scrambling which can be assimilated to a compact hyperbolic billiard, furnishing a classic example of hard chaos. It is suggested that classical chaos at large N is a crucial ingredient in reconciling the notion of fast scrambling with the required saturation of causality.

Spontaneous fragmentation of topological black holes

We study the metastability of Anti-de Sitter topological black holes with compact hyperbolic horizons. We focus on the five-dimensional case, an AdS/CFT dual to thermal states in the maximally supersymmetric large-N Yang-Mills theory, quantized on a three-dimensional compact hyperboloid. We estimate the various rates for quantum-statistical D3-brane emission, using WKB methods in the probe-brane approximation, including thermal tunneling and Schwinger pair production. The topological black holes are found to be metastable at high temperature. At low temperatures, D-branes are emitted without exponential suppression in superradiant modes, producing an instability in qualitative agreement with expectations from weakly-coupled gauge dynamics.

Holographic complexity and spacetime singularities

A bstractWe study the evolution of holographic complexity in various AdS/CFT models containing cosmological crunch singularities. We find that a notion of complexity measured by extremal bulk volumes tends to decrease as the singularity is approached in CFT time, suggesting that the corresponding quantum states have simpler entanglement structure at the singularity.

Conformal complementarity maps

A bstractWe study quantum cosmological models for certain classes of bang/crunch singularities, using the duality between expanding bubbles in AdS with a FRW interior cosmology and perturbed CFTs on de Sitter space-time. It is pointed out that horizon complementarity in the AdS bulk geometries is realized as a conformal transformation in the dual deformed CFT. The quantum version of this map is described in full detail in a toy model involving conformal quantum mechanics. In this system the complementarity map acts as an exact duality between eternal and apocalyptic Hamiltonian evolutions. We calculate the commutation relation between the Hamiltonians corresponding to the different frames. It vanishes only on scale invariant states.

Holographic Complexity Of Cold Hyperbolic Black Holes

A bstractAdS black holes with hyperbolic horizons provide strong-coupling descriptions of thermal CFT states on hyperboloids. The low-temperature limit of these systems is peculiar. In this note we show that, in addition to a large ground state degeneracy, these states also have an anomalously large holographic complexity, scaling logarithmically with the temperature. We speculate on whether this fact generalizes to other systems whose extreme infrared regime is formally controlled by Conformal Quantum Mechanics, such as various instances of near-extremal charged black holes.

Ideal gas matching for thermal Galilean holography

We exhibit a nonrelativistic ideal gas with a Kaluza-Klein tower of species, featuring a singular behavior of thermodynamic functions at zero chemical potential. In this way, we provide a qualitative match to the thermodynamics of recently found black holes in backgrounds with asymptotic nonrelativistic conformal symmetry.