In this paper, we examine static and spherically symmetric wormhole solutions in the context of Einstein–Cartan gravity, incorporating quantum corrections through the Casimir energy density as a matter source. To investigate the impact of quantum gravitational features, we apply the Generalized Uncertainty Principle (GUP), using the Dentournay, Gabriel, and Spindel (DGS) and Kempf, Mangano, and Mann (KMM) two GUP techniques. These GUP formalisms are implemented into the Casimir energy profile to investigate their effects on the wormhole geometry and matter content. We discuss the conservation equation, analyze the behavior of the null energy condition, and calculate the active gravitational mass to explore the physical acceptability of the wormhole solutions. In addition, we examine the complexity factor to describe the anisotropic character of the matter distribution filling the wormhole. The findings of this study demonstrate that GUP-induced corrections have a significant impact on the energy conditions, gravitational mass distribution, and structural complexity of the wormhole, indicating that Einstein–Cartan gravity, when incorporated with quantum vacuum effects, is capable of sustaining traversable wormhole geometries.

Saudi Arabia

Abeer Alblowy

Pakistan

M. Rizwan

Naveed Iqbal

Wael Mohammed

H. Asad

Testing complexity to diagnose wormholes existence: static and spherically symmetric case

This work analyzes the Darmois junction conditions matching an interior Alcubierre warp drive spacetime to an exterior Minkowski geometry. The joining hypersurface requires that the shift vector of the warp drive spacetime satisfy the solution of a particular inviscid Burgers equation, namely, the gauge where the shift vector is not a function of the $\textit{y}$ and $\textit{z}$ spacetime coordinates. Such a gauge connects the warp drive metric to shock waves via a Burgers-type equation, which was previously found to be an Einstein equation vacuum solution for the warp drive geometry. It is also shown that not all Ricci and Riemann tensor components are zero at the joining hypersurface; for that to happen, they depend on the shift vector solution of the inviscid Burgers equation at the joining wall. This means that the warp drive geometry is not globally flat.

Brazil

Osvaldo Santos-Pereira

Everton Abreu

Marcelo Ribeiro

Matching the Alcubierre and Minkowski spacetimes

Within a framework requiring a well-defined event horizon and matter obeying the weak energy condition, we employ gravitational decoupling method to construct non-singular hairy black holes: spherically or axially symmetric. These solutions arise from a deformation of the Minkowski vacuum, where the maximum deformation can yield the Schwarzschild metric for the static case, and the Kerr geometry for the stationary case, respectively.

China

Yaobin Hua

Zhenglong Ban

Tian-You Ren

Jia-Jun Yin

Rong-Jia Yang

Regular hairy black holes through gravitational decoupling method

We hereby address the cosmological singularity problem in a general gravitational theory invariant under Weyl conformal transformations. In particular, we focus on the Bianchi IX spacetime and we show that both the initial (big bang) and final (big crunch) singularities disappear in an infinite class of conformal frames naturally selected according to analyticity. It turns out that the past and future singularities are both unattainable within a finite affine parameter (for massless particles) or within a finite proper time (for massive and conformally coupled particles). In order to prove such a statement, we show the geodesic completion of the spacetime when probed by massless, massive, and conformally coupled particles. Finally, the chaotic behavior of the spacetime near the singularity is tamed by a conformal rescaling that turns the Bianchi IX metric into a quasi-FLRW spacetime.

Jiale Gu

Italy

Leonardo Modesto

Uzbekistan

Cosimo Bambi

Taming singularities and chaos in conformal gravity

We present the first-principles quantization of a damped scalar field within the framework of classical action principle of non-conservative systems using doubled dynamical variables. We consider a non-conservative potential term constructed to describe a linear damping of the scalar field for quantization using canonical and path-integral formalisms, and derive the two-point Green’s function along with the spectral function, which are consistent with known results from the well-known in-in formalism.

India

Kauship Saha

Sandeep Aashish

First principles quantization of a non-conservative scalar field

In the Kerr–Sen black hole, this study investigates the changes in hotspot images before and after the occurrence of magnetic reconnection. After reviewing the Comisso–Asenjo magnetic reconnection process and introducing the hotspot imaging method, we examine the temporal evolution of hotspot intensity, including when energy extraction occurs, when it does not occur, and when the observer’s azimuthal angle is altered. We also discuss the influence of the black hole’s expansion parameter and spin on hotspot imaging. The results indicate that the first flare may serve as a potential signature of ongoing energy extraction; changing the observer’s azimuthal angle may alter the time interval between the first and second flares; a larger expansion parameter makes it more difficult to identify the energy extraction signal, and a higher spin also makes it more challenging to detect the energy extraction signal.

Ke Wang

Xiao-Xiong Zeng

Hotspot images driven by magnetic reconnection in Kerr–Sen black hole

We investigate the potential of extreme mass-ratio inspirals to constrain quantum Oppenheimer–Snyder black holes within the framework of loop quantum gravity. We consider a stellar-mass object orbiting a supermassive Oppenheimer–Snyder black hole in an equatorial eccentric trajectory. To explore the dynamical behavior of the system, we analyze its orbital evolution under gravitational radiation within the adiabatic approximation and the mass-quadrupole formula for different initial orbital configurations. Our results show that the quantum correction parameter $$\hat{\alpha }$$ slows down the evolution of the orbital semi-latus rectum and eccentricity. We then employ the numerical kludge method to generate the corresponding time-domain gravitational waveforms. To assess detectability, we include Doppler modulation due to the motion of space-based detectors and compute the frequency-domain characteristic strain. By evaluating mismatches between response signals for different values of $$\hat{\alpha }$$ , we show that even small corrections $$( \hat{\alpha } \sim 10^{-5})$$ produce distinguishable effects. Our analysis suggests that future space-based detectors such as LISA can probe quantum gravitational corrections in the strong-field regime and place constraints significantly stronger than those from black hole shadow observations.

Sen Yang

Yu-Peng Zhang

Li Zhao

Yu-Xiao Liu

Constraints on quantum Oppenheimer–Snyder black holes with eccentric extreme mass-ratio inspirals

The Georgi–Machacek (GM) model extends the Higgs sector of the Standard Model by introducing additional triplets, preserving custodial symmetry at tree level and allowing large triplet vacuum expectation values (VEVs) of order $$\mathcal {O}(10)$$ GeV. Theoretical constraints on the model’s parameters include bounded-from-below (BFB) conditions for the tree-level scalar potential. This study goes beyond the BFB constraints by examining the positive definiteness of the effective potential in the GM model to ensure the absence of deeper vacua in regions with large field values. Using a one-loop renormalization group-improved (RG-improved) effective potential and new criteria for positive definiteness of homogeneous polynomials with multiple variables (necessary due to custodial symmetry breaking effects from loops), we numerically analyze these constraints. Our results reveal that the parameter ranges allowed by positive definiteness differ significantly from those derived from tree-level BFB conditions. Notably, some regions previously excluded by tree-level BFB constraints remain viable under the one-loop RG-improved scalar potential. Besides, certain parameter spaces that satisfy tree-level BFB constraints with electroweak (EW) scale couplings should be excluded due to violations of positive definiteness in large field-value regions. Our numerical analysis, based on the new criteria for positive definiteness of homogeneous polynomials with multiple variables, not only revises the GM model’s viability map but also provides a methodological template for stability studies in other extended Higgs models.

Xiaokang Du

Fei Wang

Positive definiteness constraints of effective scalar potential in Georgi–Machacek model

Thailand

David Senjaya

Erratum to: Revisiting Kerr–Newman black hole’s charged scalar cloud: flux balance

In this paper we study the shadow and quasi-normal modes (QNMs) of a black hole (BH) surrounded by a dark matter halo with Hernquist-type density distribution, which was reported in Cardoso et al. (Phys. Rev. D 105(6):L061501, 2022). In astrophysical scenarios, we find that the shadow radius enlarges as the compactness of halo increases. Therefore, we obtain an upper bound for the compactness $$\mathcal{C}\le 0.092$$ with the Event Horizon Telescope (EHT) observations. We calculate axial gravitational QNMs of the galactic BH up to $$\mathcal{C}\sim \mathcal{O}(1)$$ , and fit the redshift relative to Schwarzschild QNMs up to second order in the compactness (for $$\mathcal{C}\le 0.3)$$ . These highly redshifted QNMs, resulting from large compactness, are key to modeling the dark matter halo.

Xing-Hui Feng

Guang-Yu Zhang

Shadow and quasi-normal modes of Schwarzschild–Hernquist black hole