This paper investigates the existence of cosmological black holes by analyzing the properties of trapping horizons in detail, based on Hayward’s formalism of future outer and past inner trapping horizons, in several dynamical spacetimes embedded in an expanding universe. Through a detailed examination of the McVittie, Culetu, and Sultana–Dyer metrics, as well as the generalized Glass–Mashhoon solution, we evaluate the existence and characteristics of trapping horizons and energy conditions. The Glass–Mashhoon solution provides an analytical model for spherical stellar collapse. However, it is shown that, as long as certain conditions are satisfied, it lacks suitable future outer trapping horizons, meaning it does not represent a cosmological black hole. As a result, the McVittie class of solutions also fails to describe a cosmological black hole. Conversely, the Culetu and Sultana–Dyer spacetimes can describe a cosmological black hole in the matter-dominated early universe, provided that the relevant energy conditions are satisfied.

Iran

Mahdi Esfandiar

Fatimah Shojai

Omid Jamshidi

Soran Zoorasna

Cosmological black hole candidates: a detailed analysis of McVittie, Culetu, Sultana–Dyer, and Glass–Mashhoon spacetimes

In this study, we investigate the possibility of enhancing the di-jet resonance searches by tagging the final state radiation (FSR) jet using an event-level deep neural network. It is found that solely relying on the 4-momenta of the leading three jets allows the algorithm to achieve good discriminating power that can identify the hardest FSR jet in the signal while rejecting other soft jets. Once the invariant mass is corrected with the tagged FSR jet, the mass resolution of the signal is greatly enhanced, and the sensitivity of the search is also improved by more than 10%. By crafting the input variables carefully, the algorithm introduces minimal mass sculpting for the background, and its applicability extends to a broad mass range. This work proves that FSR jet tagging can potentially enhance di-jet resonance searches, suiting various stages of the physics programmes at the Large Hadron Collider (LHC) and High-Luminosity LHC (HL-LHC).

China

Bingxuan Liu

Yuxuan Shen

Yuanshunzi Sui

Enhancing di-jet resonance searches via a final-state radiation jet tagging algorithm * Bingxuan Liu is supported by Shenzhen Campus of the Sun Yat-sen University under project 74140-12255011, and by the Young Scientists Fund (C Class) of the National Natural Science Foundation of China (12405122). Both Yuxuan Shen and Yuanshunzi Sui are supported by College Students’ Innovative Entrepreneurial Training Plan Program

We investigated the effect of an isospin chemical potential ( $ \mu_{I} $ ) within the quark-meson model, which approximates quantum chromodynamics (QCD) by modeling low-energy phenomena such as chiral symmetry breaking and phase structure under varying conditions of temperature and chemical potential. Using the functional renormalization group (FRG) flow equations, we calculated the phase diagram in the chiral limit within the two-flavor quark-meson model in a finite $ \mu_{I} $ with $\textit{ρ}$ vector meson interactions. Fluctuation effects significantly decrease the critical chemical potential from the mean-field (MF) value $\mu_{I,{\rm MF}} \gt m_\rho$ to a lower value at which the $\textit{ρ}$ vector meson condensates alongside the chiral condensate once the isospin chemical potential exceeds the critical value $ \mu_{I}^{{\rm{crit}}} $ . This $\textit{ρ}$ condensation was investigated numerically for different meson coupling strengths. The $\textit{ρ}$ meson dominated region is delineated from other phases by a second-order phase transition at lower $ \mu_{I} $ and a first-order transition at slightly higher $ \mu_{I} $ .

Mohammed Osman

Defu Hou

Wentao Wang

United States

Hui Zhang

Functional renormalization group study of $\textit{ρ}$ meson condensate at a finite isospin chemical potential in the quark meson model * Supported in part by the National Key Research and Development Program of China (2022YFA1604900). This work is also partly supported by the National Natural Science Foundation of China (NSFC) (12435009, 12275104). Hui Zhang acknowledges the financial support from the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008) and the National Natural Science Foundation of China (12047523, 12105107)

A unique feature of gas xenon electroluminescent time projection chambers (GXeEL TPCs) in $$\beta \beta 0\nu $$ searches is their ability to reconstruct event topology, in particular to distinguish “single-electron” from “double-electron” tracks, the latter being the signature of a $$\beta \beta 0\nu $$ decay near the decay endpoint $$Q_{\beta \beta }$$ . Together with excellent energy resolution and the t $$_0$$ provided by primary scintillation, this topological information is key to suppressing backgrounds. Preserving EL, however, requires operation in pure xenon (with helium as the only benign additive), where electron diffusion is large. Consequently, reconstructed track fidelity is limited by diffusion and intrinsic EL blurring. We propose augmenting the detector with the ability to image not only the electron track but also the corresponding mirror ion track. Introducing trace amounts of $$\mathrm{NH_3}$$ ( $$\sim $$ 100 ppb) converts primary xenon ions into ammonium ions, $$\mathrm{NH_4^{+}}$$ , via a fast two-step ion–molecule process involving charge transfer followed by proton transfer, while leaving EL unaffected. Electrons drift rapidly to the anode, producing the standard EL image, whereas $$\mathrm{NH_4^{+}}$$ ions drift slowly toward the cathode, allowing time to determine the event energy and barycenter. For events in the region of interest, an ion sensor near the cathode at the projected barycenter captures the ions. Laser interrogation of the sensor’s molecular layer then reveals an ion-track image with sub-millimeter diffusion and no EL-induced smearing. Combined electron–ion imaging strengthens topological discrimination, improving background rejection by about an order of magnitude and significantly extending the discovery potential of GXeEL TPCs for very long $$\beta \beta 0\nu $$ lifetimes.

Spain

J. Gómez-Cadenas

Israel

L. Arazi

M. Elorza

Z. Freixa

F. Monrabal

A. Pazos

J. Renner

S. Soleti

S. Torelli

A journey to ITACA

It is well known that torsion waves in teleparallel Einstein gravity may induce gravitational waves (GWs). In this paper we show that a modification to Holst gravity induces low-frequency torsion waves of torsional frequency $$\sim {10^{12}Hz}= 1THz$$ as GWs sourced from astrophysical black holes. Of course, since here we use the almost Riemann-flat manifold approximation, there are no Riemannian GWs as in teleparallel spacetime but only torsionful gravitational waves. This result in Holst gravity allows us to determine an upper bound for the Barbero–Immirzi (BI) parameter as $$\gamma<<<10^{-58}$$ , which agrees with the BI bound obtained by Aliberti and Lambiase by considering matter–anti-matter asymmetry in Holst gravity. Unfortunately, this very interesting result suffers from the usual torsion ambiguity. To remedy this situation, we proceed with the BI parameter promoted to a field ore BI scalarization. Again we find a BI parameter with a bound of $$10^{-58}$$ from a terahertz-frequency torsion wave. The BI parameter is promoted to a field, and with specific approximation one obtains a BI wave equation with a plane wave solution, similar to those obtained by Taveras and Yunes. From this wave equation constant the BI parameter implies zero torsion, and consequently general relativity (GR), but the converse is not true. Higgs field variation is regarded as responsible for massive torsion. This comes from an analogy between the Higgs field and BI scalar.

Brazil

Croatia

L. Andrade

Zhi-fu Gao

Torsion mass generation induced by Einstein–Cartan gravity with a Barbero–Immirzi Higgs field analogue

Utilizing an emergent metric developed from deep learning techniques, we determine the complex potential associated with static quarkonium. This study explores the disintegration process of quarkonium by analyzing the real component of this potential, which is crucial for understanding its stability in various conditions. We show that the dissociation length, the critical distance at which a quark and antiquark pair disintegrate, decreases as the temperature increases. Furthermore, our assessment of the imaginary component of the potential indicates an increase in the magnitude of the imaginary potential for quarkonium as temperatures rise. This enhancement contributes to the quarkonium’s suppression within the quark-gluon plasma, mirroring the anticipated outcomes from QCD. Our findings not only confirm the theoretical predictions but also demonstrate the efficacy of deep learning methods in advancing our understanding of high-energy particle physics.

Mahdi Mansouri

Kazem Bitaghsir Fadafan

Xun Chen

Holographic complex potential of a quarkonium from deep learning

We analyze the latest cosmic microwave background (CMB) constraints on the scalar spectral index <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math> and tensor-to-scalar ratio <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>r</mi></math> from Planck 2018, BICEP/Keck 2018, the Atacama Cosmology Telescope Data Release 6 (ACT DR6), and the South Pole Telescope (SPT-3G) data, focusing on their implications for attractor models of inflation. We compare systematically observational bounds with theoretical predictions for both E-model (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi></math>-Starobinsky) and T-model potentials. The observational constraints accommodate E-models with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi><mo>≲</mo><mn>25</mn></math>, with the canonical Starobinsky model (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi><mo>=</mo><mn>1</mn></math>) predicting <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub><mo>=</mo><mn>0.958</mn><mi>–</mi><mn>0.963</mn></math> for reheating temperatures between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>100</mn><mo>−</mo><msup><mn>10</mn><mn>10</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, in good agreement with Planck 2018 data and within the 95% CL region determined by the Planck-ACT-SPT combination, but below the 95% confidence region of the Planck-ACT-DESI combination. Higher reheating temperatures from near-instantaneous reheating improve the compatibility. T-models predict slightly lower <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math> values (0.956–0.961), in some tension with Planck 2018 data, and we find an upper limit of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi><mo>≲</mo><mn>11</mn></math> in these models. We extend our analysis to generalized <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi></math>-attractors with monomial potentials <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi><mo stretchy="false">(</mo><mi>φ</mi><mo stretchy="false">)</mo><mo>∝</mo><msup><mi>φ</mi><mi>k</mi></msup></math> near the minimum, demonstrating that models with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>k</mi><mo>≥</mo><mn>6</mn></math> naturally predict <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub><mo>≃</mo><mn>0.965</mn><mi>–</mi><mn>0.968</mn></math> for typical number of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>e</mi></math>-folds, in better agreement with the ACT DR6 data. We also consider deformed E- and T-models, which allow significantly higher values of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>n</mi><mi>s</mi></msub></math> for low values of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>α</mi><mo>≃</mo><mn>1</mn></math>.

CERN

John Ellis

Mexico

Marcos A.G. Garcia

Keith A. Olive

Sarunas Verner

Constraints on attractor models of inflation and reheating from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>P</mi><mi>l</mi><mi>a</mi><mi>n</mi><mi>c</mi><mi>k</mi></math>, BICEP/Keck, ACT DR6, and SPT-3G data

We generalize neutrino energy density content in the early Universe near BBN era $$T\simeq 1$$ MeV within Tsallis nonextensive statistics. By using Curado–Tsallis constraints we obtain generalized distribution functions $$f_q(E)$$ . We compute the generalized thermodynamic integral for the energy density $$\rho _q$$ . We define a reescaling which is a ratio between the deformed energy density and the standard extensive case. The last was used to directly map and deform neutrino content via the effective number of neutrinos $$N_\textrm{eff}$$ . The deformation prediction was confronted against CMB+BAO and BBN data for $$N_\textrm{eff}$$ by a joint/combined $$\chi ^2$$ type-fit. We obtained the constraints $$|q-1|\le 1.09\times 10^{-2}$$ (95% CL) and $$|q-1|\le 1.32\times 10^{-2}$$ (99% CL) from the combined analysis by numerically calculating the best value of the Tsallis parameter $$q_\textrm{best}$$ .

Chile

Matias Gonzalez

Bounds on the Tsallis parameter from a deformed neutrino sector in the early Universe

We investigate the realization of a nonsingular cosmological bounce in metric $\textit{f}$($\textit{R}$) gravity using a controlled exponential deformation of the Starobinsky $$R^{2}$$ model. Adopting a smooth Gaussian-type bouncing scale factor, we first demonstrate a no-go result showing that a positive-curvature vacuum bounce cannot be supported by the model $$f(R)=R+\alpha R^{2}(1-e^{-R/R_b})$$ alone. We then show that a minimal extension obtained by introducing a constant term restores the bounce exactly, with the constant fixed algebraically by the bounce condition. A systematic parameter-space scan is performed to identify regions free of ghost and tachyonic instabilities. Working in the Einstein frame, we study the evolution of scalar and tensor perturbations across the bounce and show that both remain finite and well behaved. Our results establish a minimal, perturbatively stable realization of a vacuum bounce in $\textit{f}$($\textit{R}$) gravity that goes beyond background-level constructions.

Egypt

South Africa

G. Nashed

Saudi Arabia

A. Eid

A minimal and stable vacuum bounce in exponential $\textit{f}$($\textit{R}$) gravity

In this work, we show that stimulated decay of axions or axion-like particles in black hole superradiance is an efficient way to find and hunt primordial black holes. When de Broglie’s wavelength of the axion/ALP is comparable or larger than the black hole horizon radius, a large population of such particles accumulates in the surroundings of the black hole. When these axions/ALPs couple to photons, the bosonic cloud decays into photon pairs, generating intense stimulated radiation emission that contributes to the X-ray, visible light, and radio wave background flux that can exceed current observational limits measured at Earth. If the masses are in the interval of <math altimg='si12.svg'><mrow><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup><mtext>eV</mtext><mo linebreak='goodbreak'>&lt;</mo><mi>&#956;</mi><mo linebreak='goodbreak'>&lt;</mo><mn>1</mn><mtext>eV</mtext></mrow></math>, to be consistent with current observations of microwave background light, we found that the fraction of primordial black holes should be smaller than <math altimg='si13.svg'><mrow><msub><mi>f</mi><mrow><mi>P</mi><mi>B</mi><mi>H</mi></mrow></msub><mo linebreak='goodbreak'>&lt;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>17</mn></mrow></msup></mrow></math> for PBHs with masses within <math altimg='si14.svg'><mrow><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>13</mn></mrow></msup><msub><mi>M</mi><mo>&#8857;</mo></msub><mo linebreak='goodbreak'>&lt;</mo><msub><mi>M</mi><mrow><mi>B</mi><mi>H</mi></mrow></msub><mo linebreak='goodbreak'>&lt;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>7</mn></mrow></msup><msub><mi>M</mi><mo>&#8857;</mo></msub></mrow></math>.

Yadir Garnica

J. Barranco

Luis A. Ureña-López

Enhanced extragalactic photon flux by PBH in a stimulated axion/ALP decay scenario