arXiv subjects

Sergio Barbosa

Publications and source records attributed to Sergio Barbosa.

6 recordsLinked to original sources

arXiv2026

Running Love Numbers of Charged Black Holes

Loops of virtual particles from the vacuum of quantum field theory (QFT) render black holes tidally deformable. We compute the static tidal response of unspinning charged black holes at arbitrary radius, using the perturbative formalism developed in 2501.18684. Since the gravitational and electromagnetic tidal responses mix, we generalize the notion of Love numbers to Love matrices. We derive the coupled equations of motion for the metric and electromagnetic fluctuations around purely electric and magnetic backgrounds. For large charged black holes, which are described by the Effective Field Theory (EFT) of gravity, we compute the full set of Love matrices induced by an arbitrary tower of $F^{2n}$ operators. We find that, although quantum corrections break electromagnetic duality, the Love matrices in electric and magnetic backgrounds are related by a $Z_2$ symmetry under electric-magnetic exchange. Going beyond EFT, we compute the Love matrices of small magnetic black holes. We show that the running of the Love matrices is governed by the running of the $U(1)$ gauge coupling, and we derive the correspondence between Love and $U(1)$ beta functions for arbitrary harmonics. The overall picture that emerges is that the QFT-induced tidal response of magnetic black holes saturates in the strong-field regime. These results imply that nearly-extremal magnetic black holes charged under an Abelian dark sector could be probed by gravitational-wave observations.

hep-th↗

arXiv2025

The LHC as an Axion-Photon Collider

Assuming the existence of an axion-like particle (ALP), beams of relativistic particles emit fluxes of quasi-real ALPs, analogous to the photon fluxes described by Weizsäcker-Williams-type approximations. Consequently, ALP-ALP and ALP-photon collisions can occur at the LHC. We initiate the study of the LHC as an ALP collider, and show that ALP collisions provide competitive probes of certain ALP couplings. We show that ALP fluxes from heavy ions are suppressed relative to those from protons, unlike their photon counterpart. As a result, the most likely processes are ALP-photon collisions occurring in the proton-ion ($p$A) ultraperipheral collisions. Using our implementation of ALP fluxes in simulation tools, we show that ALP-photon collisions in $p$Pb efficiently probe ALP couplings to third generation fermions. LHC data with realistic $p$Pb luminosity can constrain the product of ALP couplings to nucleons and top quarks at the level of $O(0.01$ TeV$^{-1})$. Notably, ALP-photon collisions naturally provide the leading probe of ALP flavor-violating couplings to the top quark. We suggest that the 2016 $p$Pb dataset collected at CMS, ATLAS, and LHCb should be explored for evidence of such collisions.

hep-ph↗

arXiv2025

On The Black Hole Weak Gravity Conjecture and Extremality in the Strong-Field Regime

We point out that the Weak Gravity Conjecture (WGC) implies that sufficiently small extremal black holes are necessarily in the strong-field regime of electrodynamics, and therefore probe the UV completion of the Maxwell sector. To investigate the WGC bounds arising from these small extremal black holes, we revisit black hole decay in generic field theories in asymptotically flat space. We derive a necessary and a sufficient condition for any black hole to decay, the latter amounting to a bound on the growth of charge relative to mass. We apply these conditions to extremal black holes derived in various UV completions of the Maxwell sector. We find that the Euler-Heisenberg and DBI effective actions satisfy the sufficient condition for decay, while the ModMax model fails the necessary one, rendering it incompatible with the WGC. Using the decay conditions, we show that the black hole WGC implies positivity of the $U(1)$ gauge coupling beta function. This provides an independent argument that classically stable (embedded-Abelian) colored black holes cannot exist. We also show that the black hole WGC constrains conformal hidden sector models, and is always satisfied in their AdS dual realizations.

hep-th↗

arXiv2025

Running Love Numbers and the Effective Field Theory of Gravity

Massive states produce higher derivative corrections to Einstein gravity in the infrared, which are encoded into operators of the Effective Field Theory (EFT) of gravity. These EFT operators modify the geometry and affect the tidal properties of black holes, either neutral or charged. A thorough analysis of the perturbative tidal deformation problem leads us to introduce a tidal Green function, which we use to derive two universal formulae that efficiently provide the constant and running Love numbers induced by the EFT. We apply these formulae to determine the tidal response of EFT-corrected non-spinning black holes induced by vector and tensor fields, reproducing existing results where available and deriving new ones. We find that neutral black hole Love numbers run classically for $l\geq 3$ while charged ones run for $l\geq2$. Insights from the Frobenius method and from EFT principles confirm that the Love number renormalization flow is a well-defined physical effect. We find that extremal black holes can have Love numbers much larger than neutral ones, up to ${\cal O}(1)$ within the EFT validity regime, and that the EFT cutoff corresponds to the exponential suppression of the Schwinger effect. We discuss the possibility of probing an Abelian dark sector through gravitational waves, considering a scenario in which dark-charged extremal black holes exist in the present-day Universe.

hep-th↗

arXiv2025

Entanglement Entropy and Thermal Phase Transitions from Curvature Singularities

We study holographic entanglement entropy and revisit thermodynamics and confinement in the dilaton-gravity system. Our analysis focuses on a solvable class of backgrounds that includes AdS and linear dilaton spacetimes as particular cases, with some results extended to general warped metrics. A general lesson is that the behavior of the holographic theory is tied to the bulk curvature singularities. We find that a singular background is confining if and only if i) the singularity coincides with a boundary or ii) it is the linear dilaton. In the former case, for which the singularity cuts off spacetime, we demonstrate that both entanglement entropy and thermodynamics exhibit a first order phase transition. In the linear dilaton case we find instead that both entanglement entropy and thermal phase transitions are of second order. Additionally, along the process we thoroughly derive the radion effective action at quadratic order.

hep-th↗

arXiv2025

Background-Induced Forces from Dark Relics

Light particles quadratically coupled to nucleons induce macroscopic forces in matter. While a quantum effect always exists, an additional force occurs in the presence of a finite density of the light particles. We compute and classify such background-induced forces for particles of spin $0,\frac{1}{2},1$ in the framework of effective field theory. We show that, at short distance, the background-induced forces exhibit a universal behavior that depends solely on the moments of the phase space distribution function of the light particles. We compute the forces in the case of dark particles densities that may realistically occur in cosmology, assuming either cosmically homogeneous or virialized phase space distributions. For homogeneous distributions -- analogous to cosmic neutrinos, all the background-induced forces remain, unlike the quantum ones, exponentially unsuppressed at large distance, implying that large scale fifth force experiments are highly sensitive to dark relics. Moreover at zero mass the forces from dark bosons are generically enhanced with respect to their quantum counterpart due to Bose-Einstein distribution. Overall, we find that the resulting fifth force bounds can compete with those from quantum forces. For virialized distributions -- identifiable as cold dark matter, the reach is also enhanced beyond the dark matter Compton wavelength. We obtain significant bounds on sub-keV scalar cold dark matter, that can appear in certain cosmological scenarios. A thorough adaptation of the results from the Eöt-Wash experiment may produce powerful additional bounds.

hep-ph↗