Recent measurements from the Atacama Cosmology Telescope (ACT), combined with Planck and DESI data, suggest a scalar spectral index $$n_s$$ higher than the Planck 2018 baseline, thereby placing conventional attractor-type inflationary models such as Starobinsky $$R^2$$ and Higgs inflation under increasing tension at the $$\gtrsim 2\sigma $$ level. In this work, we examine quantum-corrected $$\phi ^4$$ inflation with a non-minimal coupling to gravity. Introducing an anomalous scaling parameter $$\gamma $$ to capture quantum corrections to the effective potential, we derive analytic expressions for the inflationary observables $$n_s$$ and $\textit{r}$. Confronting these predictions with ACT, Planck, and BAO+lensing constraints, we demonstrate that modest values of $$\gamma $$ can raise $$n_s$$ into the ACT-preferred range while maintaining a strongly suppressed tensor-to-scalar ratio. For instance, with $$N=60$$ and $$\gamma \simeq 0.006$$ , the model predicts $$n_s\simeq 0.974$$ and $$r\simeq 0.007$$ , in excellent agreement with current bounds. We further investigate preheating dynamics, focusing on particle production via parametric resonance in quantum-corrected $$\phi ^4$$ inflation with a non-minimal coupling to gravity. In this scenario, the inflaton $$\phi $$ couples to an additional scalar $$\chi $$ through an interaction $$g^{2}\phi ^{2}\chi ^{2}$$ . In Minkowski spacetime, the resonance dynamics reduce to the Mathieu equation, and we find that broad resonance can be readily achieved, leading to efficient particle production.

Thailand

Jureeporn Yuennan

Peeravit Koad

Uzbekistan

Farruh Atamurotov

Phongpichit Channuie

Quantum-corrected $$\phi ^{4}$$ inflation in light of ACT observations

In this work, we model static spherically symmetric compact stars within the framework of classical general relativity. In order to obtain exact solutions of the Einstein field equations with non-singular density profile we adopt the generalised Mak–Harko ansatz (Mak and Harko in Chin. J. Astron. Astrophys. 2:248, 2002) and demand that the complexity factor as defined by Herrera for static relativistic spheres (Herrera, Phys. Rev. D 97:044010, 2018) vanishes everywhere inside the self-gravitating object. Exact solutions of the Einstein field equations describing anisotropic fluid spheres are obtained via the gravitational decoupling method. We show that the decoupling constant, central and surface density values play a crucial role in dictating the stability of the stellar structure. The interplay between these factors accounts for mass–radius profiles associated with gravitational wave events such as GW190814 and further predicts stellar masses in the range 2.9 $$M_\odot $$ and 3.4 $$M_\odot $$ . Our models are excellent candidates for predicting compact objects such as neutron stars residing in the so-called $\textit{mass gap}$ associated with binary mergers without invoking exotic matter and modified gravity theories.

Oman

S. Maurya

China

Azerbaijan

Asifa Ashraf

Saudi Arabia

Akram Ali

South Africa

Megandhren Govender

Faisal Javed

Modeling anisotropic compact objects in the vanishing complexity regime through gravitational decoupling

Recent measurements from the Atacama Cosmology Telescope (ACT), particularly when combined with DESI baryon acoustic oscillation data, have reported a scalar spectral index <italic>n<inf>s</inf></italic> slightly higher than that inferred by <italic>Planck</italic> 2018, suggesting a mild tension with the predictions of standard inflationary attractor models. In this work, we revisit the quantum-corrected Higgs inflation scenario within the framework of a non-minimally coupled scalar field theory. Starting from the one-loop effective action, we incorporate radiative corrections through the anomalous scaling parameter <bold>A<inf>I</inf></bold> and derive analytic expressions for the inflationary observables <italic>n<inf>s</inf></italic> and <italic>r</italic> in the Einstein frame. Our analysis demonstrates that quantum corrections naturally shift <italic>n<inf>s</inf></italic> toward higher values while keeping the tensor-to-scalar ratio <italic>r</italic> suppressed. For <math altimg='si4.svg'><mrow><mi mathvariant='script'>N</mi><mo linebreak='goodbreak'>=</mo><mn>60</mn></mrow></math>, the model predicts <italic>n<inf>s</inf></italic>&#8239;&#8771;&#8239;0.9743 and <math altimg='si5.svg'><mrow><mi>r</mi><mo>&#8771;</mo><mn>5.4</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></mrow></math>, in excellent agreement with the latest ACT+DESI (P-ACT-LB) data and fully consistent with the <italic>Planck</italic> 2018 limit <italic>r</italic>&#8239;&lt;&#8239;0.036. The derived constraint <math altimg='si6.svg'><mrow><mn>4.36</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>10</mn></mrow></msup><mo linebreak='goodbreak'>&lt;</mo><mi>&#955;</mi><mo linebreak='goodbreak'>/</mo><msup><mi>&#958;</mi><mn>2</mn></msup><mo linebreak='goodbreak'>&lt;</mo><mn>10.77</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>10</mn></mrow></msup></mrow></math> confirms the robustness of the quantum-corrected Higgs framework and indicates that near-future CMB polarization experiments such as CORE, AliCPT, LiteBIRD, and CMB-S4 will be able to probe the predicted parameter space with high precision.

Radiative-corrected Higgs inflation in light of the latest ACT observations

In this paper, we examined the motion of a spinning particle around a Reissner-Nordström-like black hole. Initially, we analyze the dynamics of the spinning test particles using the Mathisson–Papapetrou–Dixon equation. Subsequently, we derive the effective potential and examine it for the parameter of the Reissner-Nordström-like black hole. We then examine the impact of the particle’s spin on the innermost stable circular orbits (ISCO), specific angular momentum, and energy at ISCO for different parameters of hairy black holes. Furthermore, we determine the critical values of the particle’s spin <math altimg='si6.svg'><mi>s</mi></math>, above which time-like particles become non-physical and space-like. Furthermore, we plot and discuss the variation of the critical spin values for different values of <math altimg='si2.svg'><mi>l</mi></math> and charge <math altimg='si3.svg'><mi>Q</mi></math>. Additionally, particle trajectories near a Reissner-Nordstr&#246;m-like (RN-like) black hole are examined for different spacetime and particle parameters. In conclusion, we analyze the center-of-mass of two spinning particles colliding near the boundary of the hairy black hole.

Gulnisa Abdukayumova

Ahmadjon Abdujabbarov

G. Mustafa

Dynamics of spinning particles around the Reissner-Nordstrom-like black hole

We investigate a novel realization of warm inflation driven by the Standard Model (SM) Higgs field within the Palatini formulation of gravity, supplemented by an $$R^2$$ curvature correction. By incorporating dissipative dynamics and a thermal radiation bath, our model eliminates the need for a separate reheating phase and naturally flattens the inflationary potential. We derive the slow-roll dynamics in the strong dissipation regime, compute the resulting inflationary observables, and demonstrate compatibility with the latest CMB constraints from Planck, BICEP/Keck, and BAO data. Specifically, we show that the scalar spectral index $$n_s$$ lies in the range 0.963–0.965, and the tensor-to-scalar ratio $\textit{r}$ is strongly suppressed, $$r \sim \mathscr {O}(10^{-3}$$ – $$10^{-2})$$ , for Higgs quartic couplings $$\lambda \sim 10^{-9}$$ . These predictions remain robust under two distinct growing-mode functions. Furthermore, we show that the model is consistent with the refined de Sitter swampland conjecture due to entropy production during inflation. This work represents the first comprehensive study of warm minimal Higgs inflation in Palatini $$R^2$$ gravity, unifying quantum gravity criteria, thermal field dynamics, and observational consistency within a single inflationary framework.

Kazakhstan

Ratbay Myrzakulov

India

P. Sahoo

Minimal warm higgs inflation in palatini $$R^{2}$$ gravity

The concept of complexity related to the celestial systems is elaborated within the context of distinct revised gravity theories. However, its interpretation in $\textit{f}$($\textit{R}$, $\textit{G}$) gravity is the main idea of our manuscript. We assume that the inner configuration of the system is a cylindrically symmetric geometry comprising the anisotropic configuration of matter. In our case study, we determine the revised equations of motion combined with the orthogonal decomposition of the Riemann tensor. The implications of anisotropic pressure and nonhomogeneous energy density are relevant. Decisive results relating to the Tolman mass, Weyl scalar, and the complexity factor are derived by incorporating dark source terms corresponding to the $\textit{f}$($\textit{R}$, $\textit{G}$) theory. Additionally, the structure scalars calculated in our manuscript are employed to derive the expression for the complexity factor, after considering reducing the complexity constraint to obtain the solutions for the specific models. The compact structures with anisotropic pressure and non-homogeneous energy density claim the maximum complexity. However, these fluids might not demonstrate any complexity if the implications of non-homogeneous energy density and anisotropic pressure are eradicated because of dark source terms corresponding to the $\textit{f}$($\textit{R}$, $\textit{G}$) theory.

Pakistan

A. Rehman

M. Yousaf

Interpretation of complexity associated with cylindrically symmetric configuration in $\textit{f}$($\textit{R}$, $\textit{G}$) theory

This study examines the black hole developed from multi-polytropic equations of state by investigating particle dynamics and various related properties, such as the radius of the horizon, the effective force, the innermost stable circular orbit radius, the photon radius, quasi-periodic oscillations, and the weak plasma lensing in uniform plasma fields, singular isothermal sphere (SIS), and non-singular isothermal gas sphere (NSIS). Furthermore, we examine the image magnification for the black hole solution. An important parameter in this black hole solution is $$c_1$$ , which significantly impacts the results. Our study shows that particle dynamics features and deflection of light are affected by the black hole parameter.

Allah Ditta

Farzan Mushtaq

Awad Ibraheem

Rana Zulqarnain

Studying the properties of particle motion and plasma lensing in regular black holes from multi-polytropic equations of state

We investigate the motion of neutral test particles around a non-rotating regular black hole within the framework of asymptotically safe gravity, analyzing the impact of the black hole’s parameters on particle motion. This black hole solution is characterized by an additional parameter, $$\eta $$ , which differentiates it from the standard Schwarzschild black hole solution. We obtain analytical formulations for the energy and angular momentum of equatorial circular orbits as functions of the black hole parameter. The stability of these circular orbits is examined by the effective potential. Additionally, we present a graphical study of the innermost stable equatorial circular orbits as functions of the black hole parameter and investigate the effective force exerted on circular orbits. We also derive the frequencies of radial and latitudinal harmonic oscillations as functions of the model parameters and discuss the key features of quasi-periodic oscillations of test particles near stable circular orbits in the black hole’s equatorial plane. The phenomenon of periastron precession is also considered. Additionally, we explore particle collisions near the black hole and demonstrate that such collisions can produce high energy near the event horizon. Our findings indicate that the black hole parameter significantly influences the motion of test particles around a regular black hole in the context of asymptotically safe gravity. We examine the shadow of black hole and using observational data from the Event Horizon Telescope (EHT) collaboration for Sgr A* and M87*, we have determined the range of $$\eta $$ parameter that corresponds to the observations.

Asalkhon Alimova

Gunel Bahaddinova

Testing regular black holes in the framework of asymptotically safe gravity using particle dynamics, QPOs, and shadow constraints

The motion of spinning particles around a quantum-corrected black hole is examined in this paper. We investigate the dynamics of spinning test particles by using the Mathisson–Papapetrou–Dixon equations, the Tulczyjew spin-supplementary condition, and restricting the motion to the equatorial plane. We determine the innermost stable circular orbit (ISCO), effective potential, and effective force and examine how these depend on the black hole’s $$\alpha $$ parameter and the particle’s $\textit{s}$ spin. However, we also take into account a superluminal bound on the motion of the spinning particle since its kinematical four-velocity and dynamical four-momentum are not always parallel. We also show how the parameter $$\alpha $$ affects the maximum value of the spin parameter $\textit{s}$. We determine the critical angular momentum of the particle for which a collision is possible by investigating collisions of spinning particles close to the horizon of a black hole. Finally, we compute the particle’s center-of-mass energy $$\mathcal {E}_{cm}$$ and analyze how the spin of the colliding particles affects it.

Impact of quantum-corrected parameter on spinning particle motion around a black hole

We investigate the dynamics of test particles around a spherically symmetric, non-rotating, hairy regular black hole, examining how the model parameters affect particle motion. The black hole is characterized by two parameters, the mass $$M$$ and a hairy parameter $$\alpha $$ . Using the effective potential, we examine the stability of circular orbits. We derive analytical expressions for the energy and angular momentum of test particles as a function of the black hole parameters. The effective forces acting on particles and the innermost stable circular orbits are also examined. Additionally, we numerically integrate the equations of motion to examine particle trajectories and further investigate their motion. Epicyclic oscillations of test particles close to the equatorial plane are explored, and analytical expressions for radial, vertical, and orbital frequencies are derived as functions of the black hole parameters. We also examine the frequency of periastron precession of the particles. We compare the motion of test particles around a hairy regular black hole with the particle motion around a classical non-rotating Schwarzschild black hole. Further, we discuss thermally fluctuating phenomena by using the Tsallis entropy and the energy emission process. Our findings show that the black hole model’s parameters significantly impact particle motion and thermal features.

Tayyab Naseer

Saibal Ray

Testing of QPOs, particle dynamics, emission energy and thermal fluctuation around a regular hairy black hole