Assuming the existence of an axionlike particle (ALP), beams of relativistic particles emit fluxes of quasireal 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 (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>p</mi><mi mathvariant="normal">A</mi></mrow></math>) ultraperipheral collisions. Using our implementation of ALP fluxes in simulation tools, we show that ALP-photon collisions in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>p</mi><mi>Pb</mi></mrow></math> efficiently probe ALP couplings to third generation fermions. LHC data with realistic <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>p</mi><mi>Pb</mi></mrow></math> luminosity can constrain the product of ALP couplings to nucleons and top quarks at the level of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>O</mi><mo stretchy="false">(</mo><mn>0.01</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>TeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup><mo stretchy="false">)</mo></mrow></math>. Notably, ALP-photon collisions naturally provide the leading probe of ALP flavor-violating couplings to the top quark. We suggest that the 2016 <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>p</mi><mi>Pb</mi></mrow></math> dataset collected at CMS, ATLAS, and LHCb should be explored for evidence of such collisions.

Brazil

Sergio Barbosa

Matheus Coelho

Sylvain Fichet

CERN

Gustavo Gil da Silveira

Magno Machado

LHC as an Axion-Photon Collider

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.

Lucas Souza

On the black hole weak gravity conjecture and extremality in the strong-field regime

Computing the vacuum expectation of a fermion number operator on a soliton background is often challenging. A recent proposal in [1] simplifies this task by considering the soliton in a bounded region and relating the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> invariant, and thus the fermion number, to a specific heat kernel coefficient and to contributions from the edge states. We test this method in a system of charged fermions living on an Abrikosov-Nielsen-Olesen vortex background. We show that the resulting <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> invariant does not depend on boundary conditions (within a certain class), thereby supporting the validity of the method. Our analysis reveals a nontrivial feature for the fermionic spectrum in the vortex-induced Higgs phase. As a by-product, we also find that for a vortex living on a disk, the edge states carry a fractional charge.

Rodrigo Fresneda

Lucas de Souza

Dmitri Vassilevich

Vortex fractional fermion number through heat kernel methods and edge states

We compute the four-photon (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math>) operators generated by loops of charged particles of spin 0, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mfrac><mn>1</mn><mn>2</mn></mfrac></math>, 1 in the presence of gravity and in any spacetime dimension <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math>. To this end, we expand the one-loop effective action via the heat kernel coefficients, which capture both the gravity-induced renormalization of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math> operators and the low-energy Einstein-Maxwell effective field theory (EFT) produced by massive charged particles. We set positivity bounds on the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math> operators using standard arguments from extremal black holes (for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>≥</mo><mn>4</mn></math>) and from infrared (IR) consistency of four-photon scattering (for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>≥</mo><mn>3</mn></math>). We find that both approaches yield nearly equivalent results, even though in the amplitudes we discard the graviton <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi></math>-channel pole and use the vanishing of the Gauss-Bonnet term at quadratic order for any <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math>. The positivity bounds constrain the charge-to-mass ratio of the heavy particles. If the Planckian <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math> operators are sufficiently small or negative, such bounds produce a version of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math>-dimensional weak gravity conjecture (WGC) in most, but not all, dimensions. In the special case of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>=</mo><mn>6</mn></math>, the gravity-induced beta functions of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math> operators from charged particles of any spin are positive, leading to WGC-like bounds with a logarithmic enhancement. In <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mo>=</mo><mn>9</mn></math>, 10, the WGC fails to guarantee extremal black hole decay in the infrared EFT, thereby requiring the existence of sufficiently large Planckian <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>F</mi><mn>4</mn></msup></math> operators.

Pedro Bittar

Gravity-induced photon interactions and infrared consistency in any dimensions

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 $\textit{i)}$ the singularity coincides with a boundary or $\textit{ii)}$ 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.

Spain

Eugenio Megías

Mariano Quirós

Entanglement entropy and thermal phase transitions from curvature singularities

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.

Background-induced forces from dark relics

We study a solvable class of five-dimensional dilaton gravity models that continuously interpolate between anti-de Sitter (AdS5), linear dilaton (LD5) and positively curved spacetimes as a function of a continuous parameter ν. The dilaton vacuum expectation value is set by a potential localized on a flat brane. We chart the elementary properties of these backgrounds for any admissible ν, and determine stability conditions of the brane-dilaton system. We find that the spectrum of metric fluctuations can be either continuous or discrete. It features a massless graviton mode confined between the brane and the curvature singularity, and a massive radion mode tied to brane-dilaton stability. We show that, in the presence of a bulk black hole, the holographic theory living on the brane features a perfect fluid. The equation of state of the holographic fluid interpolates between radiation, pressureless matter and vacuum energy as a function of ν. This extends earlier findings on holographic fluids. Our results suggest that the thermodynamics of the fluid mirrors precisely the thermodynamics of the bulk black hole.

Holographic fluids from 5D dilaton gravity

We examine the Abelian Higgs model in (d + 1)-dimensional anti-de Sitter space with an ultraviolet brane. The gauge symmetry is broken by a bulk Higgs vacuum expectation value triggered on the brane. We propose two separate Goldstone boson equivalence theorems for the boundary and bulk degrees of freedom. We compute the holographic self-energy of the gauge field and show that its spectrum is either a continuum, gapped continuum, or a discretuum as a function of the Higgs bulk mass. When the Higgs has no bulk mass, the AdS isometries are unbroken. We find in that case that the dual CFT has a non-conserved U(1) current whose anomalous dimension is proportional to the square of the Higgs vacuum expectation value. When the Higgs background weakly breaks the AdS isometries, we present an adapted WKB method to solve the gauge field equations. We show that the U(1) current dimension runs logarithmically with the energy scale in accordance with a nearly-marginal U(1)-breaking deformation of the CFT.

United States

Ian Chaffey

Philip Tanedo

Holography of broken U(1) symmetry

The linear dilaton (LD) background is the keystone of a string-derived holographic correspondence beyond <math><mrow><msub><mrow><mi>AdS</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>/</mo><msub><mrow><mi>CFT</mi></mrow><mrow><mi>d</mi></mrow></msub></mrow></math>. This motivates an exploration of the (<math><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></math>)-dimensional linear dilaton spacetime (<math><mrow><msub><mrow><mi>LD</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msub></mrow></math>) and its holographic properties from the low-energy viewpoint. We first notice that the <math><mrow><msub><mrow><mi>LD</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msub></mrow></math> space has simple conformal symmetries, that we use to shape an effective field theory (EFT) on the LD background. We then place a brane in the background to study holography at the level of quantum fields and gravity. We find that the holographic correlators from the EFT feature a pattern of singularities at certain kinematic thresholds. We argue that such singularities can be used to bootstrap the putative <math><mi>d</mi></math>-dimensional dual theory using techniques analogous to those of the cosmological bootstrap program. Turning on finite temperature, we study the holographic fluid emerging on the brane in the presence of a bulk black hole. We find that the holographic fluid is pressureless for any <math><mi>d</mi></math> due to a cancellation between Weyl curvature and dilaton stress tensor, and verify consistency with the time evolution of the theory. From the fluid thermodynamics, we find a universal temperature and Hagedorn behavior for any <math><mi>d</mi></math>. This matches the properties of a <math><mrow><msub><mrow><mi>CFT</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> with large <math><mi>T</mi><mover><mi>T</mi><mo>¯</mo></mover></math> deformation, and of little string theory for <math><mi>d</mi><mo>=</mo><mn>6</mn></math>. We also find that the holographic fluid entropy exactly matches the bulk black hole Bekenstein-Hawking entropy. Both the fluid equation of state and the spectrum of quantum fluctuations suggest that the <math><mi>d</mi></math>-dimensional dual theory arising from <math><mrow><msub><mrow><mi>LD</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msub></mrow></math> is generically gapped.

Holography of linear dilaton spacetimes from the bottom up

We initiate the study of Dyson equations of perturbative quantum field theory in anti–de Sitter (AdS) and their consequences for large-<math><mi>N</mi></math> conformal field theory (CFT). We show that the dressed one-particle AdS propagator features wave function renormalization and operator mixing, giving rise to finite corrections to one-pion exchange data. We show how the resummation of <math><mn>1</mn><mo>/</mo><mi>N</mi></math> effects in the CFT emerges from the dressing in AdS. When a boundary-to-bulk propagator is dressed by propagators whose sum of conformal dimensions is lower than the main dimension, it cannot map onto a CFT source; we relate this to an <math><mrow><mi>AdS</mi><mo>/</mo><mi>CFT</mi></mrow></math> version of particle instability. We investigate the dressing of the two-particle propagator and obtain a conformal Bethe-Salpeter equation for the conformal partial wave of a “bound state” operator. We provide a self-contained calculation for the case of a ladder kernel. We show that a bound state with conformal dimension equal to the sum of its constituents plus a <math><mn>1</mn><mo>/</mo><msup><mi>N</mi><mn>2</mn></msup></math>-suppressed “binding energy” emerges. Resummation of the Dyson equations is essential for deriving these results.