We investigate the discovery potential of a vector-like top partner ($\textit{T}$) in the Type-II Two-Higgs-Doublet Model at a high-energy $$\mu p$$ collider through the charged-Higgs cascade $$\mu ^+ p \rightarrow \nu _\mu \,{\bar{b}} T \rightarrow \nu _\mu \,{\bar{b}} H^+ b$$ with $$H^+\rightarrow t{\bar{b}}$$ . The signal is characterized by four $\textit{b}$ jets, one charged lepton, and missing transverse energy. A detector-level analysis is performed for representative spectra with $$m_{H^\pm }\simeq 600$$ –650 GeV and $$m_T\simeq 1.2$$ –1.9 TeV. We find that a $$5\sigma $$ discovery is achievable for $$m_T\simeq 1.2$$ TeV at integrated luminosities of 100 and $$150~\textrm{fb}^{-1}$$ even in the presence of $$20\%$$ background systematics. For $$m_T\simeq 1.5$$ TeV, discovery remains possible for vanishing or moderate systematics, while heavier benchmarks require larger statistics and/or improved control of backgrounds.

Morocco

R. Benbrik

M. Berrouj

Poland

M. Boukidi

H. Chatoui

M. Ech-chaouy

K. Kahime

K. Salime

Single production of a vector-like top as a probe of charged higgs bosons at a muon–proton collider

We investigate the dynamics of massive test particles around a static black hole in nonlocal gravity and examine the corresponding properties of high-frequency quasi-periodic oscillations (HF QPOs), constraining the nonlocal parameter to $$\alpha /M \le 0.452$$ . We show that the nonlocal parameter $$\alpha $$ enhances the effective potential $$V_{\text {eff}}$$ and leads to a systematic reduction in the energy $$\mathcal {E}$$ and angular momentum $$\mathcal {L}$$ of circular orbits. Consequently, the innermost stable circular orbit (ISCO) radius, along with the associated energy and angular momentum, decreases monotonically with $$\alpha $$ , while the radiative efficiency increases, reaching a maximum of approximately $$8.9\%$$ . We further analyze the fundamental orbital frequencies of test particles and find that, due to the spherical symmetry of the spacetime, the Keplerian frequency $$\Omega _{\phi }$$ and the vertical epicyclic frequency $$\Omega _{\theta }$$ coincide and are suppressed by $$\alpha $$ , whereas the radial epicyclic frequency $$\Omega _{r}$$ is enhanced. The impact of $$\alpha $$ on several twin-peak HF QPO models is examined, revealing that $$\alpha $$ increases both the lower and upper bounds of the predicted QPO frequency ranges. By imposing the $$2\nu _U = 3\nu _L$$ resonance condition, we analyze the resonant radius, upper QPO frequency, maximum allowed black hole mass, and the time delay between the shadow and QPO signals. We find that the resonant radius decreases with $$\alpha $$ , while the upper QPO frequency increases, spanning the range $$\nu _U \sim (673/M$$ – $$4360/M)\textrm{Hz}$$ . When the Tolman–Oppenheimer–Volkoff limit is imposed, the upper frequency is further constrained to $$\nu _U \lesssim 1450$$ Hz. Combining astronomical observations for the classification of QPOs, where $$\nu _U \ge 100$$ Hz, the black hole mass in the nonlocal gravity should satisfy $$M \lesssim 43.6M_\odot $$ . Although the radial separation between the resonant radius and the photon sphere decreases with $$\alpha $$ , the associated gravitational time delay increases, remaining below $$\sim 1.3\textrm{ms}$$ and thus negligible for current observational capabilities.

China

Tao-Tao Sui

Chen Long

Ye Zhang

The properties and predictions of quasi-periodic oscillations around a black hole in nonlocal gravity

We discuss how to model the surface of celestial bodies (such as stars) in quantum gravity to ensure the regularity of quantum corrections to classical solutions of general relativity at the surface of such bodies. Specifically, we use the Vilkovisky–DeWitt unique effective action to calculate universal quantum corrections to the exterior metric for a class of stellar models. Previous descriptions, obtained via a Heaviside density profile, are “pathological” at the surface of the star due to the divergence of the metric functions and associated curvature invariants. Introducing a modified version of the Tolman VII density profile, we determine the minimal degree of differentiability required for this function to generate regular quantum corrections at the star’s surface.

United Kingdom

Xavier Calmet

Marco Sebastianutti

On modelling the surfaces of celestial bodies in quantum gravity

We construct a new family of exact vacuum black brane solutions to five-dimensional Einstein gravity with a negative cosmological constant, characterized by a homogeneous horizon with Bianchi VI $$_h$$ symmetry. This construction generalizes the known Solv (Bianchi VI $$_{-1}$$ ) geometry via a continuous anisotropy parameter, $\textit{h}$. By reducing the field equations to a cohomogeneity-one system, we derive the metric analytically. These homogeneous solutions are not asymptotically (locally) AdS, but nevertheless we analyze the thermodynamics, establishing scaling relations between entropy and temperature with anisotropic holographic system in mind. Additionally, we identify a new branch of Ricci-flat, hyperscaling-violating vacuum solutions in the case where the cosmological constant vanishes.

Japan

Markus Amano

Homogeneous anisotropic black branes with bianchi VI $$_h$$ symmetry

The novel proposal to invoke the split of the Ricci scalar into bulk and boundary terms in the gravitational action, opens up a new avenue of investigation into stellar dynamics. The Lagrangian contains functional forms of the bulk term while the boundary term do not contribute to the dynamics. The advantage of the proposition is that the stellar structure equations are up to order two, thus the theory is not haunted by ghosts. We obtain explicitly the defining equations for the thermodynamical variables and the geometry for the pure quadratic case, since the linear case amounts to general relativity. In trying to establish the vacuum geometry associated with the theory it turns out that two possible metrics emerge through the vanishing of the energy-momentum tensor. Next, we analyse the isotropy equation and make the observation that it is autonomous. It is rare that this happens in astrophysical modelling. This behaviour prompted the use of dynamical systems to understand the stability properties of fixed points or invariant submanifolds. It was necessary to choose a gauge in order to split the autonomous equation into a system from which we could plot a phase portrait and deduce the stability of solution trajectories. We find that the invariant submanifolds were generally stable with nearby paths approaching them.

South Africa

Sudan Hansraj

Christian Boehmer

Ndumiso Buthelezi

Dynamical systems approach to stellar modelling in $\textit{f}$($\textit{G}$, $\textit{B}$) gravity

In this paper, we determine the relativistic bound-state solutions for the Dirac oscillator (DO) in the curved spacetime of a cloud of strings in $$(3+1)$$ -dimensions, where such solutions are given by the four-component normalized Dirac spinor and by the relativistic energy spectrum. However, unlike literature, here, we work with the spacetime in two different forms/configurations, that is, both in its original form and in its modified form. To achieve our objective, we work with the curved DO in spherical coordinates, where we use the tetrad formalism. So, by defining a stationary ansatz for the spinor, we obtain two coupled first-order differential equations, and by substituting one equation into the other, we obtain a second-order differential equation. To analytically and exactly solve this differential equation, we use a change of function and of variable. From this, we obtain the well-known Whittaker equation, whose solution is the Whittaker function. Consequently, we obtain the energy spectrum, which is quantized in terms of the radial quantum number $\textit{n}$ and the angular quantum number $$\kappa $$ , and explicitly depends on the angular frequency $$\omega $$ (describes the DO), curvature parameter $\textit{a}$ (describes the cloud of strings), and on the effective rest mass $$m_{\text {eff}}$$ (describes the rest mass modified by the curvature of spacetime). Besides, we graphically analyze the behavior of the spectrum as a function of $$\omega $$ and $\textit{a}$ for three different values of $\textit{n}$ and $$\kappa $$ , as well as the behavior of the radial probability density for four different values of $$\kappa $$ , $$\omega $$ , and $\textit{a}$ (with $$n=0$$ ).

Brazil

R. Oliveira

The Dirac oscillator in the curved spacetime of a cloud of strings

Níckolas Aguiar Alves

Lectures on the Bondi–Metzner–Sachs Group and related topics in infrared physics

In this study, we investigate the excitation of multipole transitions in quarkonium systems by high-energy photons carrying orbital angular momentum. We derive explicit expressions for the amplitude and probability of photoexcitation incorporating the dynamics of the quarkonium center of mass. It is shown that the leading contribution to the transitions induced by twisted photons comes from the multipole $$j=|m_\gamma |$$ and $$m_\gamma =l'-l$$ in the long-wave approximation. Despite the fact that similar transitions can be excited by plane-wave photons, twisted photons with $$|m_\gamma |>1$$ enable the isolation of higher multipoles offering a unique spectroscopic tool. The fulfillment of the derived selection rules imposes constraints on the parameters of the wave packet of the quarkonium center of mass, since, in general, the angular momentum can be transferred to the center of mass. As a case study, we examine the octupole transitions $$1^{3}G_3 \rightarrow 3^{3}P_0$$ and $$ 1^{3}F_3 \rightarrow 3^{3}S_1 $$ in the charmonium system. We also compare the probabilities of excitation of this multipole transition by plane-wave and twisted photons with different polarizations.

Russia

P. Korolev

V. Ryakin

Multipolar transitions excited by twisted photons in heavy quarkonia

We construct an analytic model of static semiclassical backreaction for a Schwarzschild black hole in the Hartle–Hawking state enclosed within a finite spherical cavity. Using a minimal renormalized stress–energy tensor consistent with conservation, thermal asymptotics, and horizon regularity, we integrate the reduced semiclassical Einstein equations under Dirichlet boundary conditions at the cavity wall. This yields explicit expressions for the corrections to the mass function, redshift factor, horizon location, and surface gravity. We obtain a closed-form first-order correction to the Hawking temperature in terms of a dimensionless backreaction parameter and the cavity radius. The temperature shift decomposes into redshift renormalization, geometric horizon displacement, and a local energy-density contribution at the horizon. The perturbative expansion is controlled by a parameter of order $$M_P^2/M^2$$ , ensuring validity for macroscopic black holes. The near-horizon geometry retains its universal Rindler $$^{2}\times S^{2}$$ structure, indicating that semiclassical effects renormalize rather than modify the geometric origin of Hawking radiation.

Egypt

G. Nashed

Saudi Arabia

Alnadhief Alfedeel

Romania

Tiberiu Harko

Analytic semiclassical backreaction of a Schwarzschild black hole in a finite cavity: horizon shift, temperature renormalization, and canonical stability in the Hartle–Hawking state

In this work, we construct a new family of exact five-dimensional charged and rotating asymptotically Lifshitz black holes. The spacetime solves Einstein equations coupled to a dilaton, two Abelian gauge fields, and axionic scalars supplemented by two generalized Chern-Simons terms. This configuration is characterized by a range of the free dynamical exponent $\textit{z}$ and possesses nontrivial thermodynamical parameters, where we verify the first law of black hole thermodynamics and derive the corresponding Smarr relation. As an application of this new gravitational background, we then investigate a holographic superconductor in the rotating Lifshitz background. We study the condensation of the scalar operator and the AC conductivity of the dual system. These results show that increasing the rotation parameter suppresses the condensate and weakens the superconducting phase, while increasing the dynamical critical exponent enhances the superconducting order. To the best of our knowledge, these solutions provide the first explicit family of five-dimensional rotating Lifshitz black holes supported simultaneously by electric and axionic charges.

Chile

Moisés Bravo-Gaete

Honduras

Jhony Herrera-Mendoza

Mexico

Julio Oliva

Xiangdong Zhang

Novel five-dimensional rotating Lifshitz black holes with electric and axionic charges