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Pau G. Romeu

Publications and source records attributed to Pau G. Romeu.

4 recordsLinked to original sources

Disordered Charged Horizons

We construct fully backreacted charged black brane solutions with a spatially disordered chemical potential in asymptotically AdS$_3$ and AdS$_4$, providing holographic duals of strongly coupled disordered systems. At intermediate temperatures these geometries display highly inhomogeneous horizons, though their geometric averages reproduce the clean BTZ and Reissner-Nordström solutions. The low temperature behavior, however, differs sharply between dimensions. In AdS$_3$, inhomogeneities decay and the horizon flows to the clean charged BTZ fixed point, rendering disorder irrelevant in the infrared. In AdS$_4$, horizon inhomogeneities persist: while the averaged geometry flows to the clean AdS$_2\times \mathbb{R}^2$ throat, the disordered horizon induces a finite residual resistivity. These results show that disorder can qualitatively alter the IR physics of holographic metals and indicate violations of the Harris criterion in strongly coupled systems.

hep-th↗

Pseudospectra of holographic diffusion: gauge fields breaking free from the master scalar

We study pseudospectra of quasinormal frequencies and complex linear momenta of a U(1) gauge field in a Schwarzschild black branes in Anti-de Sitter. We present a novel approach for computing the pseudospectra which uses directly the gauge field variables and contrast it to a conventional master scalar field approach. Upon clarifying a subtlety in the energy norm of the master scalar we show that the pseudospectra of both approaches conincide. In the hydrodynamic regime we find that the hydrodynamic quasinormal frequency, the diffusive mode, is spectrally stable to a very good approximation. On the other hand hydrodynamic complex linear momenta show enhanced spectral instability as a consequence of a pole-collision at zero frequency.

hep-th↗

Chiral Magnetic Effect enhancement at lower collision energies

We extend previous holographic studies of the Chiral Magnetic Effect (CME) by incorporating a time-dependent magnetic field. Various magnetic field profiles proposed in the literature are implemented, and their impact on the CME signal is analyzed in both static and expanding backgrounds. Interestingly, the integrated chiral magnetic current can exhibit a non-monotonic dependence on the collision energy. Our results suggest that the CME signal is enhanced at collision energies below $\sqrt{s}=200$ GeV. In addition, we derive a quasi-equilibrium formula for the chiral magnetic effect in the expanding background that is valid at late times.

hep-ph↗

Pseudospectra of complex momentum modes

We initiate the study of stability and pseudospectra of complex momentum modes of asymptotically anti-de Sitter black holes. Similar to quasinormal modes, these can be defined as the poles of the holographic Green's function, albeit for real frequency and complex momentum. Their pseudospectra are in stark contrast to the pseudospectra of quasinormal modes of AdS black holes. Contrary to the case of quasinormal mode pseudospectra, the resolvent is well-defined, and the numerical approximation shows fast convergence. At zero frequency, complex momentum modes are stable normal modes of a Hermitian operator. Even for large frequencies, they show only comparatively mild spectral instability. We also find that local potential perturbations cannot destabilize the lowest complex momentum mode.

hep-th↗