Research lines

Quantum field theory in curved spacetimes is the extension of quantum field theory to non-trivial backgrounds. It can be considered as a low curvature regime of a more fundamental theory of quantum gravity, valid when the backreaction of the quantum fluctuations on the geometry is negligible. 

In our group we explore phenomena of quantum field theory in non-trivial backgrounds such as particle creation in black holes (Hawking radiation) or in flat spacetime in the presence of non-trivial background electromagnetic fields (Schwinger effect). 

In the past years, we have devoted special attention to the production of dark matter particles in cosmological scenarios like the early universe, adding minimal and non-minimal couplings of the dark matter fields to gravity as well as possible non-local effects. Another important aspect of our analyses from recent years has to do with fixing the ambiguities that appear in the quantization. 

Black holes are one of the most important theoretical predictions of general relativity.  They have curvature singularities hidden behind an event horizon. Albeit encompassing one of the most popular fields of study inside general relativity for the last century, the true nature of black hole singularities keeps puzzling theorists.

Quantum theories of gravity are expected to solve this problem. Semiclassical gravity consitutes the first step towards a theory of quantum gravity, as it incorporates the backreaction of quantum matter fields on the geometry. These quantum fluctuations of matter fields can dramatically affect the outcome of a gravitational collapse, for instance, regularizing singularities and making horizons disappear.   

We study dynamical scenarios in which semiclassical effects drive a quick evaporation of the trapped region. In relation to this, we investigate the role of quantum effects and the mass inflation mechanism in inner horizons of charged and rotating black holes. 

The undesirable properties of general relativistic black holes motivate the study of alternative regular models. They need to pass current astrophysical constraints and hence "mimic" many black hole properties. We study and constrain the universal properties that these objects should display. 

Our concrete proposal for black hole mimickers is the black star. Black stars are semiclassical stellar configurations sustained by vacuum energy. They do not have singularities nor horizons, and their surface is extremely close to a "would-be horizon". They share many of the observational properties with black holes, making them indistinguishable via optical observations. Gravitational wave experiments, on the other hand, could reveal whether these objects are realized in Nature or not.

Loop Quantum Gravity (LQG) is one of the main candidates for a consistent theory of quantum gravity. It is a nonperturbative, background independent approach based on a reformulation of general relativity as a gauge theory. We focus on the application of LQG techniques to symmetry-reduced models. On the one hand, we study Loop Quantum Cosmology (LQC) which applies to cosmological models, such as the homogeneous and isotropic FLRW universe. On the other hand,  we apply LQG quantization techniques to black hole spacetimes. 

LQC resolves the classical Big Bang singularity: it gets replaced by a quantum bounce connecting a contracting branch of the universe with an expanding one. We consider the inclusion of inhomogeneities which play a central role in current cosmology. We investigate the so-called hybrid LQC approach, which handles homogeneous and inhomogeneous sectors differently. The bounce scenario remains despite the inhomogeneities, allowing us to compute quantum gravity corrections to cosmological observables like the primordial power spectrum. 

We study the discrete and Planckian quantum geometry that replaces the singularity in the interior of the Schwarzschild black hole. These quantum corrections are negligible for the exterior region and classical general relativity is recovered as a low curvature limit. We also consider dynamical situations in which collapsing matter forms a black hole. All these scenarios open new windows for the study of quantum gravity effects in black hole scenarios that might be experimentally tested in future years.

We also dive in foundational questions in LQC and LQG, such as the Problem of Time. In the canonical approach to quantization, the Universe does not evolve and we must account for evolution in a relational way, but there are several choices involved in the process. These have non-trivial consequences in the dynamics of the Universe. We analyse them in cosmological models. 

We study analogues of general relativistic gravitational fields within other physical systems, typically condensed matter systems. They provide insights into semiclassical physics, since their regimes of relevance are close to the observational regimes of usual condensed matter systems. Generically, such analogue gravitational fields do not obey Einstein-like equations. Our actual work focuses on understanding whether these effective geometries could develop such dynamics in some regime. If so, it would constitute a theory of quantum gravity with an ordinary many-body system as a microscopic UV completion. 

The possible appearance of emergent massless spin-2 excitations, the mediators of the gravitational interactions usually called gravitons, is one of the key cornerstones of emergent gravity. We study the conditions under which gauge symmetries emerge in physical systems. We use self-consistency criteria to constrain the non-linear completions of linearized emergent gauge theories. Finally, we analyze the interplay of Lorentz invariance violations at high energies, which we expect in emergent gravity, and their impact on effective field theories. 

Relativistic Quantum Information (RQI) constitutes a field theoretical approach to quantum communication and quantum information processing in relativistic settings. We use Unruh-DeWitt detectors, a qubit coupled to a quantum field, as a local probe of the quantum field fluctuations. We focus on the study of the Unruh effect, the perception of flat spacetime vacuum as a thermal state by an accelerated observer, and the vacuum state of ultracompact objects. 

We study the Unruh effect in arbitrary spacetime dimensions for different quantum fields and with different couplings. We focus on thermalization properties of accelerating Unruh-DeWitt detectors in flat space vacuum, such as the thermalization time scale. We study the quantization of fields on the geometries of ultracompact objects and analyze the response of Unruh-DeWitt detectors coupled to them.  

Coming soon!