In this study, we analyze $\textit{f}$($\textit{R}$) gravity employing the $$ f(R) = R+ \alpha _1 R^p - \alpha _2 R^{-q} $$ model within the Friedmann–Lemaître–Robertson–Walker (FLRW) background. We derive the Friedmann equations via modified gravity action and subsequently reexpress them in terms of the standard Friedmann equations. Our investigation explores the behavior of a bouncing cosmological model within this modified gravity context, offering a potential solution to the singularity problem encountered in the standard Big Bang cosmology. We represent cosmological parameters as functions of cosmic time and scrutinize the conditions for a cosmic bounce. Additionally, we reconstruct the $\textit{f}$($\textit{R}$) gravity model using the redshift parameter and graphically present cosmological parameters as functions of redshift. These plots reveal an accelerated nature of Universe expansion. Furthermore, we reconstruct $\textit{f}$($\textit{R}$) gravity models for scale factors, $$a(t) = e^{e^{\lambda t}}$$ which exhibits the bouncing behavior. Finally, we investigated the stability scenario by examining the sound speed. The resulting graph of sound speed plotted against redshift confirms late-time stability.

Pakistan

M. Ilyas

Saudi Arabia

Khalid Masood

South Korea

Nehad Shah

Dynamical analysis of bouncing cosmology in the Capozziello–De Laurentis model of $\textit{f}$($\textit{R}$) gravity

We study the production of (pseudo-) scalar particles, in general coined as axion-like particles (ALPs) in association with electrons and neutrinos in the muon decay process. For this purpose, we compute the decay width of the muon to a four-body channel using a $$d=7$$ effective operator that couples the ALP to the Standard Model fermions, namely leptons and neutrinos. Assuming a dominant coupling of the ALP to the dark sector, we only consider ALP decays to invisible final states. To obtain constraints on our model using the existing measurements, we leverage data from the TRIUMF Weak Interaction Symmetry Test (TWIST) experiment and obtain bounds on the ALP-lepton coupling for masses in the range of $$0< m_{\phi } < m_{\mu }/4$$ , as allowed by kinematics. Using the precision of current TWIST measurements, we obtain an order of magnitude estimation necessary for future searches to further constrain the parameter space for such a setup. Furthermore, we find that keeping realistic considerations, the new physics contribution can possibly be enhanced even with a minimalistic modification to the fiducial area used in the experiment potentially allowing for stronger constraints. At the end, in an attempt to relax the assumption that ALP decays to invisible only, we also investigate its stability and find potential longevity within collider environments for the mass range considered in this study.

Netherlands

Ankita Budhraja

India

Samadrita Mukherjee

Austria

Sahana Narasimha

Leptophilic (pseudo)scalars with TWIST data for polarized muon decays

We propose a covariant extension of general relativity in which the local effective dimension of spacetime is promoted to a dynamical, curvature-induced field on an underlying four-dimensional manifold. Deviations from four dimensions are encoded in a scalar degree of freedom $$\varepsilon (x)$$ , defining $$D_{\textrm{eff}}(x)=4-\varepsilon (x)$$ , which enters the gravitational action through a dimension weight $$v(\varepsilon )$$ multiplying the Einstein–Hilbert term and a scalar potential $$U(\varepsilon )$$ . At the level of the field equations, these ingredients combine into a curvature-sensitive effective potential $$V(\varepsilon ,R)$$ for the dynamical dimension field, where $\textit{R}$ is the Ricci scalar. In the limit $$\varepsilon \rightarrow 0$$ and $$v(\varepsilon )\rightarrow 1$$ , the weak-field regime of general relativity is continuously recovered. We derive the modified Einstein equations and the equation of motion for $$\varepsilon $$ , showing that the resulting framework is scalar–tensor-like in structure, with the additional field controlling the local effective dimensionality of spacetime rather than describing an independent matter component. As benchmark applications, we study static, spherically symmetric configurations and a spatially flat Friedmann–Lemaître–Robertson–Walker background, where curvature-induced dimensional effects lead to controlled deformations of the mass–radius relation in compact objects and small corrections to the background expansion history.

Türkiye

L. Yıldız

D. Kaykı

E. Güdekli

Curvature-induced dynamical effective spacetime dimension in an extension of general relativity

Ultralight dark matter (ULDM) has emerged as a compelling alternative to the standard cold dark matter (CDM) model by forming quantum-pressure-supported solitonic cores that address small-scale structure anomalies. In this work, we investigate the dynamics of solitons in ULDM by numerically evolving scalar field configurations under gravity, incorporating a range of interaction terms. We analyse soliton formation, stability, and collisions driven solely by quantum pressure and gravity, focusing first on the non-interacting case. We then introduce self-interactions via quartic, axion monodromy, logarithmic, and Sinh-Gordon potentials, each inducing distinct dynamical behaviour: repulsive quartic terms enhance stability, attractive interactions can lead to collapse, axion monodromy introduces saturation effects that modify core compactness, logarithmic terms suppress central density growth, and Sinh-Gordon interactions lead to deformation and fragmentation at high strengths. In order to analyse the effect of photon interactions beyond self-interactions, we observe the destabilization of solitonic structures even in the absence of scalar self-couplings. When both self- and photon-interactions are incorporated, soliton dynamics become highly sensitive to the specific potential, significantly influencing post-collision behaviour and long-term coherence. We provide a comprehensive analysis of soliton dynamics in ULDM across varying interaction types and parameter regimes, highlighting the complex dynamical behaviour of these quantum structures.

Zayana T

S. Veni

Impact of self-interaction and photon interactions on solitonic structures in ultralight dark matter

Thermal interactions are ubiquitous in the cosmos, driving systems toward equilibrium. In this work, we investigate the evolution of thermal states across the early universe, encompassing the inflationary, radiation-dominated (RD), and matter-dominated (MD) eras, through the lens of Krylov complexity. Utilizing a purification scheme, we map the thermal state to a two-mode pure state, facilitating an open-system analysis of Krylov complexity in contrast to closed-system methodologies. Our numerical results demonstrate that Krylov complexity grows exponentially during inflation, indicating chaotic behavior, before saturating at nearly constant values in the RD and MD eras due to particle production via preheating. Furthermore, we analyze the Krylov entropy, which exhibits an evolutionary trend analogous to that of complexity. Crucially, our analysis reveals a dynamical transition in the universe’s dissipative nature: with the universe acting as a strongly dissipative system during inflation and transitioning to a weakly dissipative regime in the subsequent eras. These findings provide a novel quantum information perspective on early universe dynamics.

China

Tao Li

Lei-Hua Liu

Krylov complexity of thermal state in early universe

In this work, we theoretically investigate strong gravitational lensing effects and evaluate various lensing observables of a static, spherically symmetric solution in the context of effective quantum gravity (EQG). Among the three types of solutions proposed in EQG backgrounds, this is the third type without having Cauchy horizons. This solution gives rise to black hole as well as horizonless wormhole solutions depending on the range of values of the parameters of the theory. Based on the data from SgrA* and M87* observations, possible bounds on the parameter are obtained. It is found that the horizonless wormhole solution is ruled out by SgrA* observations, but is allowed by M87* observations. We analyze and provide estimates of the lensing observables, some of which can potentially be detected by observational tools.

Suvankar Paul

Strong gravitational lensing by compact object without Cauchy horizons in effective quantum gravity

Studying heavy-quark hadrons is crucial due to the nonperturbative nature of low-energy QCD, with Heavy-Quark Symmetry (HQS) serving as a key framework for understanding their spin and flavor symmetries. However, a key issue is that the theoretically expected $$B^{(*)}\bar{K}$$ molecular states have not yet been observed, although they are considered the bottom-quark counterparts of the observed $$\bar{D}^{(*)}\bar{K}$$ molecular states (corresponding to $$D_{s0}(2317/2460)^{-}$$ ), which challenges the universality of HQS. The main goal of this work is to search for the theoretically predicted $$B\bar{K}$$ and $$B^{*}\bar{K}$$ molecular states, namely $$B_{s0}^{*}(5725)$$ and $$B_{s1}^{*}(5778)$$ , via the reactions $$K^{-}p \rightarrow \varLambda _{b}^{0} B_{s0}^{*}$$ and $$K^{-}p \rightarrow \varLambda _{b}^{0} B_{s1}^{*}$$ . Within an effective Lagrangian framework, we compute the relevant cross sections, considering $\textit{t}$-channel $$B^{(*)}$$ exchanges and $$K^{-}p$$ initial-state interactions (ISI). The results show that the production cross sections of $$B_{s0}^{*}(5725)$$ and $$B_{s1}^{*}(5778)$$ can reach the order of 0.01 nb, and we suggest that experiments searching for $$B_{s0}^{*}(5725)$$ are best performed at $$P_{K^{-}} = 12.18~\textrm{GeV}$$ , while higher energies are most favorable for producing $$B_{s1}^{*}(5778)$$ . The ISI play a crucial role, as they not only significantly enhance the production cross sections of $$B_{s0}^{*}(5725)$$ and $$B_{s1}^{*}(5778)$$ (by roughly one order of magnitude) but also markedly affect the angular distributions of the produced particles. We also calculated the production cross sections of the conventional quark–antiquark states $$B_{s0}^*(5700)$$ and $$B_{s1}^*(5720)$$ , which are found to be nearly the same as those of $$B_{s0}^{*}(5725)$$ and $$B_{s1}^{*}(5778)$$ . Although their internal structures remain ambiguous, these results can inform future experimental searches at CERN and J-PARC.

Min Yuan

Yin Huang

A search for $$B_{s0}^{*}$$ and $$B^{*}_{s1}$$ through the $$K^{-}p$$ interaction

The Belle Collaboration recently reported a potential candidate for the spin-2 $$D^*\bar{D}^*$$ partner of the $\textit{X}$(3872), denoted as $$X_2$$ , with a mass of $$(4014.3\pm 4.0\pm 1.5)$$ MeV and a width of $$(4\pm 11\pm 6)$$ MeV. Assuming the $$X_2$$ as a $$D^*\bar{D}^*$$ molecular state, we calculate its hidden charm decay $$X_2 \rightarrow \pi ^+ \pi ^- \eta _{c}$$ via box loop diagram using an effective Lagrangian approach. To investigate the dependence of the decay width on the molecular structure, we consider four different phase angles: $$\theta =0$$ , $$\pi /6$$ , $$\pi /4$$ , and $$\pi /2$$ . The decay width is found to be sensitive to the mass of the $$X_2$$ . The decay partial widths are predicted to be on the order of 1 keV. We expect that the present calculations, performed in the molecular framework, would provide useful guidance for future experimental studies.

Hao-Dong Cai

Gang Li

Shi-Dong Liu

Hidden charmed decays of spin-2 partner of $\textit{X}$(3872) within $$D^*\bar{D}^*$$ molecular framework

The Three-Higgs-Doublet Model (3HDM) extends the Standard Model by introducing two additional scalar doublets, leading to a rich spectrum of new particles: three neutral CP-even Higgs bosons $$(h_1,$$ $$H_2,$$ $$H_3),$$ two neutral CP-odd Higgs bosons $$(A_2,$$ $$A_3),$$ and two charged Higgs bosons $$(H_2^+,$$ $$H_3^+).$$ In this work, we present a phenomenological study of the 3HDM at the future International Linear Collider (ILC) with a center-of-mass energy of $$\sqrt{s} = 1000\,\text {GeV}.$$ Applying a comprehensive set of theoretical and experimental constraints, we identify promising new physics signals with sufficiently large production cross-sections. Our analysis shows that $$e^+e^- \rightarrow H_2 A_2,$$ $$e^+e^- \rightarrow H_2 H_2 Z,$$ $$A_2 A_2 Z,$$ $$H_2 H_2^{\pm } W^{\mp },$$ $$A_2 H_2^{\pm } W^{\mp }$$ and $$H_1 H_2 A_2$$ are among the most sensitive channels to probe this extended Higgs sector. We demonstrate that a future ILC would offer a powerful platform to test these interactions and discover these heavier Higgs bosons thus providing evidence of physics beyond the Standard Model.

Baradhwaj Coleppa

Akshat Khanna

Gokul Krishna

ILC phenomenology of the $$Z_3$$ symmetric type-Z three Higgs doublet model

In this article, we investigate the bound orbits of the timelike particles and the gravitational waveforms emitted from these orbits around a renormalization group improved Kerr black hole in the framework of the asymptotic safety approach. The running Newton coupling in the metric is characterized by two free quantum parameters $$(\omega ,\,\gamma )$$ arising from the non-perturbative renormalization group theory and the appropriate cutoff identification, respectively. As expected, the radii of the horizon, the marginally bound orbits and the innermost stable orbit are all decrease as the quantum parameters increase. Under the extreme mass-ratio inspirals approximation the deviation of gravitational waveforms radiated by the periodic orbits from those in the classical Kerr background increases with the two quantum parameters. However, this effect is much smaller in the retrograde case compared to the prograde case. Especially, by comparing the characteristic strain of those gravitational wave with the sensitivity curve of several potential detectors, we find that their characteristic frequencies can fall within the sensitivity ranges of several planned gravitational wave observatories, suggesting that such signals may be detectable with sufficient instrumental sensitivity.

Yong-Zhuang Li

Xiao-Mei Kuang

The bound orbits and gravitational waveforms of timelike particles around renormalization group improved Kerr black holes