This work establishes a series of no-go conjectures that impose rigorous constraints on the zero mode localization of bulk fields in braneworld scenarios, specifically affecting gauge and spinor fields within five-dimensional spacetimes. Our approach differs from traditional methods as it does not rely on specific equations of motion, making our results broadly applicable across various braneworld models. These no-go conditions reveal fundamental limitations in field localization, challenging the feasibility of embedding fields on the brane. For instance, our analysis demonstrates that existing models fail to achieve consistent localization for gauge and spinor fields. Additionally, one of our conditions indicates that the effective Lagrangian on the brane cannot exhibit conformal invariance.

Brazil

G. Alencar

R. Costa Filho

Georgia

M. Gogberashvili

Constraints on bulk fields: no-go conjectures for braneworld models

Massless higher-spin fields show no preference for any value of the cosmological constant in 3$\textit{d}$. All matter-free higher-spin gravities in 3d are equivalent to Chern-Simons theories with an appropriate choice of gauge algebra. For various reasons, including holography, it is important to enrich them with matter fields. In ($\textit{A}$)$\textit{dS}$ , the coupling of matter fields to higher-spin fields is well-known to the leading order and is determined by the representation theory. We extend this result to flat space, where the relevant higher-spin algebra is the Poisson algebra, aka $\textit{w}$ . However, we show that both in flat and ($\textit{A}$)$\textit{dS}$ spaces there are no nontrivial higher order deformations/interactions. Nevertheless, by enlarging the field content with some auxiliary fields and taking advantage of the chiral higher-spin gravity’s vertices, it is possible to construct an exotic matter-coupled theory on ($\textit{A}$)$\textit{dS}$ that is perturbatively local. It also admits a flat limit. The equations of motion have the form of a Poisson sigma-model and a meaningful action has the form of a Courant sigma-model. We also explore the potential for embedding this theory into a holographic duality.

Russia

Alexey Sharapov

Belgium

Evgeny Skvortsov

Arseny Sukhanov

Matter-coupled higher spin gravities in 3$\textit{d}$: no- and yes-go results

<p>We consider a general dynamical, spherically symmetric background in the cubic subclass of Horndeski theory and obtain the quadratic action for the perturbations. We analyze the stability conditions for high-energy modes and study the issue of the no-go theorem. We formulate the no-go theorem for weak dependence on one variable (time or radial) and derive its generalization to the cases which could be reduced by coordinate transformation to scenarios where the scalar field has weak dependence on one of the coordinates. Moreover, we show that a wide class of singular solutions is also prohibited within the cubic subclass of Horndeski theory.</p>

S. Mironov

M. Sharov

No-Go theorem in the cubic subclass of Horndeski theory for spherically symmetric dynamical background

The Bekenstein–Hawking equation states that black holes should have entropy proportional to their areas to make black hole physics compatible with the second law of thermodynamics. However, this equation leads to an inconsistency among the first law of black hole mechanics, the entropy conservation law of quantum mechanics, and a heuristic picture for Hawking radiation—creation of entangled pairs near the horizon. Here we propose an equation alternative to the Bekenstein–Hawking equation from the viewpoint of quantum information, to resolve this inconsistency without changing Hawking’s original pair-creation picture for the radiation. This argues that the area of any stationary black hole, including Kerr and charged ones, is proportional to the coherent information—which is “minus” the conditional entropy defined only in the quantum regime—from the outside, to the black hole excluding negative-frequency particles generated by Hawking’s pair creation. Our equation suggests that negative-frequency particles inside a black hole behave as if they have “negative” entropy. Our result implies that a black hole stores purely quantum information, rather than classical information, and the area of the event horizon describes the number of Bell pairs that can be distilled between the interior and exterior.

Japan

Koji Azuma

United Kingdom

Sathyawageeswar Subramanian

Go Kato

Do Black Holes Store Negative Entropy?

We show how a nonlocal gravitational interaction can circumvent the Weinberg no-go theorem on cosmological constant, which forbids the existence of any solution to the cosmological constant problem within the context of local field theories unless some fine-tuning is assumed. In particular, Infinite Derivative Gravity theories hint at a possible understanding of the cosmological constant as a nonlocal gravitational effect on very large scales. In this perspective, one can describe the observed cosmic acceleration in terms of an effective field theory without relying on the fine-tuning of parameters or additional matter fields.

Italy

Salvatore Capozziello

Netherlands

Anupam Mazumdar

Giuseppe Meluccio

The Weinberg no-go theorem for cosmological constant and nonlocal gravity

We examine the possibility of Primordial Black Holes (PBHs) formation in single field models of inflation. Using the adiabatic or wave function renormalization scheme in the short range modes, we show that one-loop correction to the power spectrum is free from quadratic UV divergence. We consider a framework in which PBHs are produced during the transition from Slow Roll (SR) to Ultra Slow Roll (USR) followed by the end of inflation. We demonstrate that the renormalized power spectrum soften the contribution of the logarithmic IR divergence and severely restricts the possible mass range of produced PBHs in the said transition, namely,  $$M_\textrm{PBH}\sim 10^{2}\,\textrm{g}$$  <math> <mrow> <msub> <mi>M</mi> <mtext>PBH</mtext> </msub> <mo>∼</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="0.166667em"></mspace> <mtext>g</mtext> </mrow> </math>    $$\hat{\textrm{a}}$$  <math> <mover> <mtext>a</mtext> <mo>^</mo> </mover> </math>   la a no-go theorem. In particular, we find that the produced PBHs are short lived ( $$t^\textrm{evap}_\textrm{PBH}\sim 10^{-20}\,\textrm{s}$$  <math> <mrow> <msubsup> <mi>t</mi> <mtext>PBH</mtext> <mtext>evap</mtext> </msubsup> <mo>∼</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>20</mn> </mrow> </msup> <mspace width="0.166667em"></mspace> <mtext>s</mtext> </mrow> </math>  ) and the corresponding number of e-folds in the USR region is restricted to  $$\Delta {\mathcal {N}}_\textrm{USR}\approx 2$$  <math> <mrow> <mi>Δ</mi> <msub> <mi>N</mi> <mtext>USR</mtext> </msub> <mo>≈</mo> <mn>2</mn> </mrow> </math>  .

India

Sayantan Choudhury

Mayukh Gangopadhyay

Kazakhstan

China

M. Sami

No-go for the formation of heavy mass Primordial Black Holes in Single Field Inflation

We present a novel artificial intelligence approach for beyond the Standard Model parameter space scans by augmenting an evolutionary strategy with novelty detection. Our approach leverages the power of evolutionary strategies, previously shown to quickly converge to the valid regions of the parameter space, with a novelty reward to continue exploration once converged. Taking the <math><mrow><msub><mrow><mi>Z</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></math> 3HDM as our physics case, we show how our methodology allows us to quickly explore highly constrained multidimensional parameter spaces, providing up to eight orders of magnitude higher sampling efficiency when compared with pure random sampling and up to four orders of magnitude when compared to random sampling around the alignment limit. In turn, this enables us to explore regions of the parameter space that have been hitherto overlooked, leading to the possibility of novel phenomenological realizations of the <math><msub><mi>Z</mi><mn>3</mn></msub></math> three Higgs doublet model that had not been considered before.

Portugal

Jorge Crispim Romão

Miguel Crispim Romão

Combining evolutionary strategies and novelty detection to go beyond the alignment limit of the <math><mrow><msub><mrow><mi>Z</mi></mrow><mrow><mn>3</mn></mrow></msub></mrow></math> 3HDM

Generic models in Galileons or Horndeski theory do not have cosmological solutions that are free of instabilities and singularities in the entire time of evolution. We extend this no-go theorem to a spacetime with torsion. On this more general geometry the no-go argument now holds provided the additional hypothesis that the graviton is also subluminal throughout the entire evolution. Thus, critically different for Galileons’ stability on a torsionful spacetime, an arguably unphysical although arbitrarily short (deep UV) phase occurring at an arbitrary time, when the speed of gravity <math><mo>(</mo><msub><mi>c</mi><mi>g</mi></msub><mo>)</mo></math> is slightly higher than luminal (<math><mi>c</mi></math>), and by at least an amount <math><msub><mi>c</mi><mi>g</mi></msub><mo>≥</mo><msqrt><mn>2</mn></msqrt><mi>c</mi></math>, can lead to an all-time linearly stable and nonsingular cosmology. As a proof of principle we build a stable model for a cosmological bounce that is almost always subluminal, where the short-lived superluminal phase occurs before the bounce, and that transits to general relativity in the asymptotic past and future.

M. Valencia-Villegas

Stability of nonsingular cosmologies in Galileon models with torsion: A no-go theorem for eternal subluminality

The travel times of light signals between two antipodal points on the surface of a compact star are calculated for two different trajectories: a straight line that passes through the center of the star and a semi-circular trajectory that connects the antipodal points along the surface of the star. Interestingly, it is explicitly proved that, for highly dense stars, the longer trajectory (the one that goes along the surface of the star) may be characterized by the shorter travel time as measured by asymptotic observers. In particular, for constant density stars we determine analytically the critical value of the dimensionless density-area parameter <math><mi>Λ</mi><mo>≡</mo><mn>4</mn><mi>π</mi><msup><mrow><mi>R</mi></mrow><mrow><mn>2</mn></mrow></msup><mi>ρ</mi></math> that marks the boundary between situations in which a direct crossing of the star through its center has the shorter travel time and situations in which the semi-circular trajectory along the surface of the star is characterized by the shorter travel time as measured by asymptotic observers [here <math><mo>{</mo><mi>R</mi><mo>,</mo><mi>ρ</mi><mo>}</mo></math> are respectively the radius of the star and its density].

Israel

Shahar Hod

Compact stars: To cross or go around? That is the question

We derive a set of no-go theorems and yes-go examples for the parity-odd primordial trispectrum of curvature perturbations. We work at tree-level in the decoupling limit of the Effective Field Theory of Inflation and assume scale invariance and a Bunch-Davies vacuum. We show that the parity-odd scalar trispectrum vanishes in the presence of any number of scalar fields with arbitrary mass and any parity-odd scalar correlator vanishes in the presence of any number of spinning fields with massless de Sitter mode functions, in agreement with the findings of Liu, Tong, Wang and Xianyu [1]. The same is true for correlators with an odd number of conformally-coupled external fields. We derive these results using both the (boostless) cosmological bootstrap, in particular the Cosmological Optical Theorem, and explicit perturbative calculations. We then discuss a series of yes-go examples by relaxing the above assumptions one at the time. In particular, we provide explicit results for the parity-odd trispectrum for (i) violations of scale invariance in single-clock inflation, (ii) the modified dispersion relation of the ghost condensate (non-Bunch-Davies vacuum), and (iii) interactions with massive spinning fields. Our results establish the parity-odd trispectrum as an exceptionally sensitive probe of new physics beyond vanilla inflation.