In General Relativity, the tidal Love numbers of black holes vanish, implying they are resistant to tidal deformation. This “rigidity” is easily broken in the presence of higher-derivative corrections. Focusing on extremal charged black holes in Einstein-Maxwell EFT, we compute the static linear response for both the vector ($\textit{ℓ}$ = 1) and parity-odd tensor ($\textit{ℓ}$ ≥ 2) sectors. We find that the resulting tidal Love numbers are non-zero and exhibit logarithmic running, a hallmark of quantum corrections. Crucially, we show that the sign of these deformations is not arbitrary; the induced electric and magnetic susceptibilities and their log runnings in the $\textit{ℓ}$ = 1 sector are constrained by unitarity and the Weak Gravity Conjecture. Furthermore, due to gravito-electromagnetic mixing, we find the cross log runnings and show that they are the same, which we explain through the worldline effective field theory.

Japan

Toshifumi Noumi

China

Sam Wong

Extremal Love: tidal/electromagnetic deformability, logarithmic running and the weak gravity conjecture

<p>Motivated by the cosmological collider program, which aims to probe high-energy physics through inflation, we investigate the phase diagram of multiflavor QCD in de Sitter spacetime with a flavor-universal axial chemical potential induced by a rolling inflaton coupled to fermions. We determine the first-order critical line and a critical point as functions of the Hubble parameter and the axial chemical potential, employing an effective description of chiral symmetry breaking within the framework of the Nambu–Jona-Lasinio model. We find that a first-order chiral phase transition may occur during inflation or at its end when the axial chemical potential is sufficiently large and crosses the critical line. This serves as a benchmark cosmological analog of the QCD phase diagram explored in heavy-ion colliders.</p>

Kohei Fujikura

Inflationary QCD phase diagram

We study causality constraints on black hole thermodynamics in nonlinear electrodynamics, where the Lagrangian is taken to be an arbitrary function of the electromagnetic field strength tensor. By requiring the absence of superluminal propagation, we show that the mass-to-charge ratio of extremal black holes exhibits a certain monotonicity previously studied in the context of the weak gravity conjecture. Furthermore, under the same condition, we demonstrate that the entropy-to-mass-squared ratio of black holes, which we interpret as an entropy density, decreases monotonically with increasing mass, while keeping the mass-to-charge ratio fixed. This new monotonicity property extends previous studies on the positivity of four-derivative corrections to black hole entropy in the microcanonical ensemble to all orders in nonlinear electrodynamics.

Yoshihiko Abe

France

Maxime Médevielle

Kaho Yoshimura

Causality constraints on black hole thermodynamics in nonlinear electrodynamics

We study perturbative unitarity bounds on the field-space curvature in de Sitter spacetime, using the momentum-space entanglement approach recently proposed by Duaso Pueyo, Goodhew, McCulloch, and Pajer. As an illustration, we perform a perturbative computation of the purity in two-scalar models and compare the resulting unitarity bounds with those obtained via a flat space approximation. In particular, we find that perturbative unitarity imposes an upper bound on the field-space curvature of the Hubble scale order, in addition to a bound analogous to the flat space result. This reflects the thermal nature of de Sitter spacetime. We also discuss generalizations to higher-dimensional field spaces.

Qianhang Cai

Tomoya Inada

Masataka Ishikawa

Kanji Nishii

Perturbative unitarity bounds on field-space curvature in de Sitter spacetime: purity vs scattering amplitude

We compute the holographic entanglement entropy via the Ryu-Takayanagi prescription in the three-dimensional Friedmann-Lemaître-Robertson-Walker universe. We consider two types of holographic scenarios analogous to the static patch holography and half de Sitter holography, in which the holographic boundary is timelike and placed in the bulk. We find in general that strong subadditivity can be satisfied only in the former scenario, and, in addition, the holographic boundary must lie within the apparent horizon. Also, for the universe filled with an ideal fluid with constant equation of state $\textit{w}$ < –1, the condition is sharpened as that the holographic boundary must lie within the event horizon instead. These constraints provide necessary conditions for the dual quantum field theory to be standard and compatible with strong subadditivity.

South Korea

Fumiya Sano

Yu-ki Suzuki

Holographic entanglement entropy in the FLRW universe

We elaborate on the effective field theory (EFT) construction for dissipative open systems coupled to dynamical gravity, in light of recent developments on the EFT of dissipative hydrodynamics (HydroEFT). Our construction is based on the Schwinger-Keldysh formalism and its symmetries as well as microscopic unitarity. A key aspect of dynamical gravity is that gravity couples to all degrees of freedom universally, hence the EFT has to take into account the energy-momentum tensor of the environment to which the energy escapes from the dissipative system of interest. We incorporate this effect by modeling the environment based on HydroEFT, assuming validity of the derivative expansion of the environment sector. For illustration, we apply our EFT recipe to a dissipative scalar field coupled to dynamical gravity that can be used, e.g., for dissipative inflation. In particular we quantify impacts of fluctuations in the environment sector on the scalar dynamics. We also apply the same framework to dissipative gravity, discussing dissipative gravitational waves and the generalized second law of black hole thermodynamics.

Pak Lau

Gravitational EFT for dissipative open systems

We derive the cutoff length scale of the quadratic gravity in <math><mi>d</mi><mo>≥</mo><mn>5</mn></math> dimensional spacetime by demanding that the quantum focusing conjecture for the smeared quantum expansion holds at the classical level. The cutoff scale has a different dependence on the spacetime dimension depending on the sign of the coupling constant of the quadratic gravity. We also investigate a concrete example of the five-dimensional Schwarzschild spacetime and directly confirm that the quantum focusing conjecture holds when the quantum expansion is smeared over the scale larger than our cutoff scale.

Takamasa Kanai

Kengo Maeda

Daisuke Yoshida

Cutoff scale of quadratic gravity from quantum focusing conjecture

We investigate a gedanken experiment to destroy an extremally charged black hole by dropping a test particle, provided that there are multiple <math><mrow><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow></math> gauge fields coupled with each other through higher derivative interactions. It is known that the Coulomb repulsion prevents a test particle that would break the extremal condition from falling into an extremal black hole and therefore the black hole cannot be destroyed. We extend this observation to include higher derivative corrections. Although the extremal condition is modified by the higher derivative interactions, we find that the repulsive force induced by the higher derivative couplings is responsible for preventing a test particle that would break the modified extremal condition to reach the event horizon. Thus, we confirm that the weak cosmic censorship conjecture holds for extremally charged black holes even in the presence of higher derivative corrections, as long as the test particle approximation is justified.

Keisuke Izumi

Gedanken experiments to destroy a black hole by a test particle: Multiply charged black hole with higher derivative corrections

The gravitational positivity bound gives quantitative “swampland” constraints on low-energy effective theories inside theories of quantum gravity. We give a comprehensive discussion of this bound for those interested in applications to phenomenological model building. We present a practical recipe for deriving the bound, and discuss subtleties relevant for realistic models. As an illustration, we study the positivity bound on the scattering of the massive gauge bosons in the Higgs/Stückelberg mechanism. Under certain assumptions on gravitational amplitudes at high energy, we obtain a lower bound <math><msub><mi>m</mi><mi>V</mi></msub><mo>≳</mo><msubsup><mi>Λ</mi><mi>UV</mi><mn>2</mn></msubsup><mo>/</mo><mi>g</mi><msub><mi>M</mi><mi>Pl</mi></msub></math> on the gauge boson mass <math><msub><mi>m</mi><mi>V</mi></msub></math>, where <math><mi>g</mi></math> is the coupling constant of the gauge field, <math><msub><mi>M</mi><mi>Pl</mi></msub></math> is the reduced Planck mass and <math><msub><mi>Λ</mi><mi>UV</mi></msub></math> is the ultraviolet cutoff of the effective field theory. This bound can strongly constrain new physics models involving a massive gauge boson. We also discuss how the bound depends on our high-energy assumptions.

Katsuki Aoki

Ryo Saito

Sota Sato

Satoshi Shirai

Junsei Tokuda

Masahito Yamazaki

Gravitational positivity for phenomenologists: Dark gauge boson in the swampland

Massive fields can imprint unique oscillatory features on primordial correlation functions or inflationary correlators, which is dubbed the cosmological collider signal. In this work, we analytically investigate the effects of a time-dependent mass of a scalar field on inflationary correlators, extending previous numerical studies and implementing techniques developed in the cosmological bootstrap program. The time-dependent mass is in general induced by couplings to the slow-roll inflaton background, with particularly significant effects in the case of non-derivative couplings. By linearly approximating the time dependence, the mode function of the massive scalar is computed analytically, on which we derive analytic formulae for two-, three-, and four-point correlators with the tree-level exchange of the massive scalar. The obtained formulae are utilized to discuss the phenomenological impacts on the power spectrum and bispectrum, and it is found that the scaling behavior of the bispectrum in the squeezed configuration, i.e., the cosmological collider signal, is modified from a time-dependent Boltzmann suppression. By investigating the scaling behavior in detail, we are in principle able to determine the non-derivative couplings between the inflaton and the massive particle.