arXiv subjects

Nicolas Grandi

Publications and source records attributed to Nicolas Grandi.

12 recordsLinked to original sources

arXiv2026

Holographic metals at finite volume

We construct the electron star solution in asymptotically global AdS spacetime, and investigate its stability properties, both locally under perturbations and globally with respect to the Reissner-Nordstr\"om black hole and thermal AdS metrics. We interpret the resulting phase diagram as that of a holographic metal confined to a finite volume. We identify a quantum critical point at finite chemical potential, around which the different phases are organized.

hep-th↗

arXiv2024

De Sitter geometric inflation from dynamical singularities

Within the framework of geometric inflation, where the Friedmann equation is modified to incorporate an infinite series of higher curvature corrections, we describe the emergence of a de Sitter inflationary phase near the poles of an arbitrary dynamical function. Our analysis is quite general and does not depend on any specific choice of cosmological dynamics.

hep-th↗

arXiv2023

Exact oscillations and chaos on a non-Abelian coil

We construct new exact solutions of the Georgi-Glashow model in $3+1$ dimensions. These configurations are periodic in time but lead to a stationary energy density and no energy flux. Nevertheless, they possess a characteristic frequency which manifests itself through non-trivial resonances on test fields. This allows us to interpret them as non-Abelian self sustained coils. We show that for larger energies a transition to chaotic behavior takes place, which we characterize by Poincar\'e sections, Fourier spectra and exponential growth of the geodesic deviation in an effective Jacobi metric, the latter triggered by parametric resonances.

hep-th↗

arXiv2019

Holographic metals at finite doping

We construct the electron star solution to the model that was recently proposed by Kiritsis and Li in order to describe a holographic superconductor at finite doping. We do so by finding a map between the doped model and the standard undoped one. In this way, we are able to describe the holographic metallic phase at finite doping. In particular, we study the gauge field fluctuations and find the dependence of the electric conductivity on the doping parameter.

hep-th↗

arXiv2019

On four-dimensional Einsteinian gravity, quasitopological gravity, cosmology and black holes

We show that the combination of cubic invariants defining five-dimensional quasitopological gravity, when written in four dimensions, reduce to the version of four-dimensional Einsteinian gravity recently proposed by Arciniega, Edelstein & Jaime, that produces second order equations of motion in a FLRW ansatz, with a purely geometrical inflationary period. We introduce a quartic version of the four-dimensional Einsteinian theory with similar properties, and study its consequences. In particular we found that there exists a region on the space of parameters which allows for thermodynamically stable black holes, as well as a well-defined cosmology with geometrically driven inflation. We briefly discuss the cosmological inhomogeneities in this setup. We also provide a combination of quintic invariants with those properties.

hep-th↗

arXiv2018

Scalar Hair Around Charged Black Holes in Einstein-Gauss-Bonnet Gravity

We explore charged black hole solutions in Einstein-Gauss-Bonnet gravity in five dimensions, with a charged scalar hair. We interpret such hairy black holes as the final state of the superradiant instability previously reported for this system. We explore the relation of the hairy black hole solutions with the non-backreacting quasibound states and scalar clouds, as well as with the boson star solutions.

gr-qc↗

arXiv2017

Superradiance of charged black holes in Einstein-Gauss-Bonnet Gravity

In this paper we show that electrically charged black holes in Einstein-Gauss-Bonnet gravity suffer from a superradiant instability. It is triggered by a charged scalar field that fulfills Dirichlet boundary conditions at a mirror located outside the horizon. As in General Relativity, the unstable modes exist provided the mirror is located beyond a critical radius, making the instability a long wavelength one. We explore the effects of the Gauss-Bonnet corrections on the critical radius and find evidence that the critical radius decreases as the Gauss-Bonnet coupling $α$ increases. Due to the, up to date, lack of an analytic rotating solution for Einstein-Gauss-Bonnet theory, this is the first example of a superradiant instability in the presence of higher curvature terms in the action.

hep-th↗

arXiv2016

Approximate analytic expression for the Skyrmions crystal

We find approximate solutions for the two-dimensional non-linear Σ-model with Dzyalioshinkii-Moriya term, representing magnetic Skyrmions. They are built in an analytic form, by pasting different approximate solutions found in different regions of space. We verify that our construction reproduces the phenomenology known from numerical solutions and Monte Carlo simulations, giving rise to a Skyrmion lattice at an intermediate range of magnetic field, flanked by spiral and ferromagnetic phases for low and high magnetic field respectively.

cond-mat.str-el↗

arXiv2013

Vortex solutions of the Lifshitz-Chern-Simons theory

We study vortex-like solutions to the Lifshitz-Chern-Simons theory. We find that such solutions exists and have a logarithmically divergent energy, which suggests that a Kostelitz-Thouless transition may occur, in which voxtex-antivortex pairs are created above a critical temperature. Following a suggestion made by Callan and Wilzcek for the global U(1) scalar field model, we study vortex solutions of the Lifshitz-Chern-Simons model formulated on the hyperbolic plane, finding that, as expected, the resulting configurations have finite energy. For completeness, we also explore Lifshitz-Chern-Simons vortex solutions on the sphere.

cond-mat.str-el↗

arXiv2010

Wormhole solutions to Horava gravity

We present wormhole solutions to Horava non-relativistic gravity theory in vacuum. We show that, if the parameter $λ$ is set to one, transversable wormholes connecting two asymptotically de Sitter or anti-de Sitter regions exist. In the case of arbitrary $λ$, the asymptotic regions have a more complicated metric with constant curvature. We also show that, when the detailed balance condition is violated softly, tranversable and asymptotically Minkowski, de Sitter or anti-de Sitter wormholes exist.

hep-th↗

arXiv2009

The Cosmological Slingshot Scenario: Myths and Facts

We generalize the Cosmological Slingshot Scenario for a Slingshot brane moving in a Klebanov-Strassler throat. We show that the horizon and isotropy problems of standard cosmology are avoided, while the flatness problem is acceptably alleviated. Regarding the primordial perturbations, we identify their vacuum state and elucidate the evolution from the quantum to the classical regimes. Also, we calculate their exact power spectrum showing its compatibility with current data. We discuss the bouncing solution from a four dimensional point of view. In this framework the radial and angular motion of the Slingshot brane are described by two scalar fields. We show that the bouncing solution for the scale factor in String frame is mapped into a monotonically increasing (in conformal time) solution in the Einstein frame. We finally discuss about the regularity of the geometry in Einstein frame.

hep-th↗

arXiv2008

The Cosmological Slingshot Scenario: a Stringy Proposal for the Early Time Cosmology

In the Cosmological Slingshot Scenario, our Universe is a D3-brane that extends in the 4d noncompact directions of a warped Calabi-Yau compactification of IIB Supergravity. Early time cosmology corresponds to a period in which the brane moves inside a warped throat where a non-vanishing angular momentum ensures that the trajectory of the brane has a turning point. The corresponding induced metric on the D3-brane experiences a cosmological evolution with a bounce. In this framework, the homogeneity, flatness, and isotropy problems of standard cosmology might be avoided. The power spectrum of primordial perturbations of the brane embedding can be found and it is shown to be in agreement to WMAP data.

hep-th↗