Islands and Page curves in 4d from Type IIB

Variants of the black hole information paradox are studied in Type IIB string theory setups that realize four-dimensional gravity coupled to a bath. The setups are string theory versions of doubly-holographic Karch/Randall brane worlds, with black holes coupled to non-gravitating and gravitating baths. The 10d versions are based on fully backreacted solutions for configurations of D3, D5 and NS5 branes, and admit dual descriptions as $$ \mathcal{N} $$ N = 4 SYM on a half space and 3d $$ {T}_{\rho}^{\sigma } $$ T ρ σ [SU(N)] SCFTs. Island contributions to the entanglement entropy of black hole radiation systems are identified through Ryu/Takayanagi surfaces and lead to Page curves. Analogs of the critical angles found in the Karch/Randall models are identified in 10d, as critical parameters in the brane configurations and dual field theories.

Vector fields localization on brane worlds

To confine vector bosons in the four dimensional sector of a domain wall spacetime, we propose a mechanism in which the interaction among vectors is propagated via the self-interaction of the scalar wall. In the process, the vector acquires an asymptotic mass, defined by the bulk cosmological constant, and it ends up coupled to the wall by the tension of the brane. The mechanism is applied on the Randall Sundrum scenario and regular versions of it, and on singular domain walls. In any case, the electrostatic potential between two charged particles is defined by both the vector state attached to the wall and a continuous tower of massive vector states that propagate freely along the scenario's extra dimension.

Tensor perturbations and thick branes in higher-dimensional f(R) gravity

We study brane worlds in an anisotropic higher-dimensional spacetime within the context of f(R) gravity. Firstly, we demonstrate that this spacetime with a concrete metric ansatz is stable against linear tensor perturbations under certain conditions. Moreover, the Kaluza-Klein modes of the graviton are analyzed. Secondly, we investigate thick brane solutions in six dimensions and their properties. We further exhibit two sets of solutions for thick branes. At last, the effective potential of the Kaluza-Klein modes of the graviton is discussed for the two solved f(R) models in higher dimensions.

Can neutron disappearance/reappearance experiments definitively rule out the existence of hidden braneworlds endowed with a copy of the Standard Model?

Many works, aiming to explain the origin of dark matter or dark energy, consider the existence of hidden (brane)worlds parallel to our own visible world — our usual Universe — in a multidimensional bulk. Hidden braneworlds allow for hidden copies of the Standard Model. For instance, atoms hidden in a hidden brane could exist as dark matter candidates. As a way to constrain such hypotheses, the possibility for neutron–hidden neutron swapping can be tested thanks to disappearance-reappearance experiments also known as passing-through-walls neutron experiments. The neutron-hidden neutron coupling [Formula: see text] can be constrained from those experiments. While [Formula: see text] could be arbitrarily small, previous works involving a [Formula: see text] bulk, with DGP branes, show that [Formula: see text] then possesses a value which is reachable experimentally. It is of crucial interest to know if a reachable value for [Formula: see text] is universal or not and to estimate its magnitude. Indeed, it would allow, in a near future, to reject definitively — or not — the existence of hidden braneworlds from experiments. In the present paper, we explore this issue by calculating [Formula: see text] for DGP branes, for [Formula: see text], [Formula: see text] and [Formula: see text] bulks. As a major result, no disappearance-reappearance experiment would definitively universally rules out the existence of hidden worlds endowed with their own copy of Standard Model particles, except for specific scenarios with conditions reachable in future experiments.

de Sitter in non-supersymmetric string theories: no-go theorems and brane-worlds

We study de Sitter configurations in ten-dimensional string models where supersymmetry is either absent or broken at the string scale. To this end, we derive expressions for the cosmological constant in general warped flux compactifications with localized sources, which yield no-go theorems that extend previous works on supersymmetric cases. We frame our results within a dimensional reduction and connect them to a number of Swampland conjectures, corroborating them further in the absence of supersymmetry. Furthermore, we construct a top-down string embedding of de Sitter brane-world cosmologies within unstable anti-de Sitter landscapes, providing a concrete realization of a recently revisited proposal.

Brane cosmology and the self-tuning of the cosmological constant in the presence of bulk black holes

Motivated by the holographic self-tuning proposal of the cosmological constant, we generalize and study the cosmology of brane-worlds embedded in a higher-dimensional bulk black hole geometry. We describe the equations and matching conditions in the case of flat, spherical and hyperbolic slicing of the bulk geometry and find the conditions for the existence of a static solution. We solve the equations that govern dynamical geometries in the probe brane limit and we describe in detail the resulting brane-world cosmologies. Of particular interest are the properties of solutions when the brane-world approaches the black hole horizon. In this case the geometry induced on the brane is that of de Sitter, whose entropy and temperature is related to those of the higher dimensional bulk black hole.