Eur Phys Research Articles

Constraints on metric-Palatini gravity from QPO data

AbstractIn this work, we study metric-Palatini gravity extended by the antisymmetric part of the affine curvature. This gravity theory leads to general relativity plus a geometric Proca field. Using our previous construction of its static spherically-symmetric AdS solution (Eur Phys J. C 83(4):318, 2023), we perform a detailed analysis in this work using the observational quasiperiodic oscillations (QPOs) data. To this end, we use the latest data from stellar-mass black hole GRO J1655-40, intermediate-mass black hole in M82-X1, and the super-massive black hole in SgA* (our Milky Way) and perform a Monte-Carlo-Markov-Chain (MCMC) analysis to determine or bound the model parameters. Our results shed light on the allowed ranges of the Proca mass and other parameters. The results imply that our solutions can cover all three astrophysical black holes. Our analysis can also be extended to more general metric-affine gravity theories.

Yukawa–Casimir wormholes in the framework of f(R) gravity

In this article, we explore the Yukawa modification of the Casimir wormhole within the framework of f(R) gravity. To accomplish this, we adopt an approach proposed by Garattini (Eur Phys J C 81:824, 2021), wherein the original Casimir source is modified by a Yukawa term in three distinct scenarios. We utilize these Yukawa Casimir energy densities to assess the feasibility of traversable wormholes. The resulting shape function satisfies the criteria for traversability under the specified parameter values. Furthermore, we scrutinize the energy conditions and the violation of the null energy conditions suggests the presence of exotic matter within the Yukawa Casimir wormholes. Additionally, we analyze the embedding procedures for the wormhole geometry.

Axial gravitational quasi-normal modes of spherically symmetric black hole in f(R) gravity and its optical appearance

This paper investigates the axial gravitational perturbations originating from spherically symmetric black holes in f(R) gravity, along with the optical appearance of such a black hole. The aim is to search for evidence of the existence of these black holes in astrophysical observations and thereby test the correctness of the f(R) theory. In literature Kalita and Mukhopadhyay (Eur Phys J C 79:877, 2019), the spherically symmetric black hole metric in f(R) gravity is obtained. By comparing it with the metric for spherically symmetric black holes in general relativity, we find that the modification of gravity due to f(R) can be described in this black hole spacetime using a parameter Cf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C_f$$\\end{document}. Next, we study axial gravitational perturbations in this spacetime and successfully derive a decoupled axial perturbation equation. We also discuss the impact of f(R) gravity on the quasi-normal mode frequencies. Additionally, we have also investigated the optical appearance of the black hole. We discuss the impact of the parameter Cf\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C_f$$\\end{document} on the observable characteristics of the accretion disk. In principle, both of these effects can be observed using gravitational wave detectors and astronomical telescopes.

Monte Carlo evaluation of divergent one-loop integrals without contour deformation

Reference (Pittau and Webber in Eur Phys J C 82(1):55, https://doi.org/10.1140/epjc/s10052-022-10008-6, 2022) introduces a method for computing numerically four-dimensional multi-loop integrals without performing an explicit analytic contour deformation around threshold singularities. In this paper, we extend such a technique to massless scalar one-loop integrals regularized in the framework of dimensional regularization. A two-loop example is also discussed.

Quantum gravity modifications to the accretion onto a Kerr black hole

In the framework of the Asymptotic Safety scenario for quantum gravity, we analyze quantum gravity modifications to the thermal characteristics of a thin accretion disk spiraling around a renormalization group improved (RGI-) Kerr black hole in the low energy regime. We focused on the quantum effects on the location of the innermost stable circular orbit (ISCO), the energy flux from the disk, the disk temperature, the observed redshifted luminosity, and the accretion efficiency. The deviations from the classical general relativity due to quantum effects are described for a free parameter that arises in the improved Kerr metric as a consequence of the fact that the Newton constant turns into a running coupling G(r) depending on the energy scale. We find that, both for rapid and slow rotating black holes with accretion disks in prograde and retrograde circulation, increases in the value of this parameter are accompanied by a decreasing of the ISCO, by a lifting of the peaks of the radiation properties of the disk and by an increase of the accretion mass efficiency, as compared with the predictions of general relativity. Our results confirm previously established findings in Zuluaga and Sánchez (Eur Phys J C 81:840, 2021) where we showed that these quantum gravity effects also occur for an accretion disk around a RGI-Schwarzschild black hole.

Towards a realistic setup for a dynamical measurement of deviations from Newton’s 1/r2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/r^2$$\\end{document} law: the impact of air viscosity

A novel experimental setup to measure deviations from the 1/r2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/r^2$$\\end{document} distance dependence of Newtonian gravity was proposed in Donini and Marimón (Eur Phys J C 76:696, 2016). The underlying theoretical idea was to study the orbits of a microscopically-sized planetary system composed of a “Satellite”, with mass mS∼O(10-9)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_{\ extrm{S}} \\sim {\\mathcal {O}}(10^{-9})$$\\end{document} g, and a “Planet”, with mass MP∼O(10-5)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M_{\ extrm{P}} \\sim {\\mathcal {O}} (10^{-5}) $$\\end{document} g at an initial distance of hundreds of microns. The detection of precession of the orbit in this system would be an unambiguous indication of a central potential with terms that scale with the distance differently from 1/r. This is a huge advantage with respect to the measurement of the absolute strength of the attraction between two bodies, as most electrically-induced background potentials do indeed scale as 1/r. Detection of orbit precession is unaffected by these effects, allowing for better sensitivities. In Baeza-Ballesteros et al. (Eur Phys J C 82:154, 2022), the impact of other subleading backgrounds that may induce orbit precession, such as, e.g., the electrical Casimir force or general relativity, was studied in detail. It was found that the proposed setup could test Yukawa-like corrections, α×exp(-r/λ),\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha \ imes \\exp (-r/\\lambda ),$$\\end{document} to the 1/r potential with couplings as low as α∼10-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha \\sim 10^{-2}$$\\end{document} for distances as small as λ∼10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda \\sim 10$$\\end{document}μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m, improving by roughly an order of magnitude present bounds. In this paper, we start to move from a theoretical study of the proposal to a more realistic implementation of the experimental setup. As a first step, we study the impact of air viscosity on the proposed setup and see how the setup should be modified in order to preserve the theoretical sensitivity achieved in Donini and Marimón (2016) and Baeza-Ballesteros et al. (2022).

Possible existence of Rastall–Rainbow wormholes in dark matter galactic halos

The Rastall–Rainbow gravity theory has recently been proposed as a combination of the Rastall and rainbow theories. This theory can be thought as a generalization of the Rastall gravity to an energy dependent Rastall theory, and leads to an additional degrees of freedom. In this paper, we construct models that admit the wormhole geometries within this theory. We analyze the properties of static wormholes based on the profiles of dark matter halos, which was demonstrated earlier in Rahaman et al. (Eur Phys J C 74:2750, 2014) that galactic halo possesses the necessary properties in favour of the existence of wormholes. The main properties are being analyzed by considering three different kinds of halo density profiles. Our results indicate that such wormholes could potentially exist but the NEC is violated in the vicinity of the wormhole throat. We have further examined the stability of the configuration through the adiabatic sound velocity.

Gravity-induced entanglement between two massive microscopic particles in curved spacetime: II. Friedmann–Lemaître–Robertson–Walker universe

In our previous work (Zhang and Shu in Eur Phys J. C 84(3):256, 2024), we have explored quantum gravity induced entanglement of masses (QGEM) in curved spacetime, observing entanglement formation between particles moving along geodesics in a Schwarzschild spacetime background. We find that long interaction time induces entanglement, even for particles with microscopic mass, addressing decoherence concerns. In this work, we build upon our previous work (Zhang and Shu 2024) by extending our investigation to a time-dependent spacetime. Specifically, we explore the entanglement induced by the mutual gravitation of massive particles in the Friedmann–Lemaître–Robertson–Walker (FLRW) universe. With the help of the phase shift and the QGEM spectrum, our proposed scheme offers a potential method for observing the formation of entanglement caused by the quantum gravity of massive particles as they propagate in the FLRW universe. Consequently, it provides insights into the field of entanglement in cosmology.

Simulations of galaxies in an expanding Universe with modified Newtonian dynamics (MOND) and with modified gravitational attractions (MOGA)

The stability of galaxies is either explained by the existence of dark matter or caused by a modification of Newtonian acceleration (MOND). Here, we show that the modification of the Newtonian dynamics can equally well be obtained by a modification of Newton’s law of universal gravitational attraction (MOGA) when Newton’s inverse square attraction from a distant object is replaced with an inverse attraction. This modification is often proposed in the standard model, and with the modification of the attraction caused by dark matter. The recently derived algorithm, Eur Phys J Plus, 137:99, 2022; Class Quantum Grav, 39:225006, 2022, for classical celestial dynamics is used to simulate models of the Milky Way in an expanding universe and with either MOND or MOGA. The simulations show that the galaxies with MOND dynamics are unstable, whereas MOGA stabilizes the galaxies. The rotation velocities for objects in galaxies with classical Newtonian dynamics decline inversely proportional to the square root of the distance r to the center of the galaxy. But the rotation velocities is relatively independent of r for MOGA and qualitatively in agreement with experimentally determined rotation curves for galaxies in the Universe. The modification of the attractions may be caused by the masses of the objects in the central part of the galaxy by the lensing of gravitational waves from far-away objects in the galaxy.

Conserved spin operator of Dirac’s theory in spatially flat FLRW space-times

New conserved spin and orbital angular momentum operators of Dirac’s theory on spatially flat FLRW space-times are proposed generalizing thus the recent results concerning the role of Pryce’s spin operator in the flat case (Cotăescu in Eur Phys J C, 82, 1073, 2022). These operators split the conserved total angular momentum generating the new spin and orbital symmetries that form the rotations of the isometry groups. The new spin operator is defined and studied in active mode with the help of a suitable spectral representation giving its Fourier transform. Moreover, in the same manner is defined the operator of the fermion polarization. The orbital angular momentum is derived in passive mode using a new method, inspired by Wigner’s theory of induced representations, but working properly only for global rotations. In this approach the quantization is performed finding that the one-particle spin and orbital angular momentum operators have the same form in any FLRW spacetime regardless their concrete geometries given by various scale factors.

Updates on the determination of |Vcb|,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert ,$$\\end{document}R(D∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R(D^{*})$$\\end{document} and |Vub|/|Vcb|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{ub} \\vert /\\vert V_{cb} \\vert $$\\end{document}

We present an updated determination of the values of |Vcb|,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert ,$$\\end{document}R(D∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R(D^*)$$\\end{document} and |Vub|/|Vcb|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{ub} \\vert /\\vert V_{cb} \\vert $$\\end{document} based on the new data on semileptonic B→D∗ℓνℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B \\rightarrow D^* \\ell \ u _\\ell $$\\end{document} decays by the Belle and Belle-II Collaborations and on the recent theoretical progress in the calculation of the form factors relevant for semileptonic B→D∗ℓνℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B \\rightarrow D^* \\ell \ u _\\ell $$\\end{document} and Bs→Kℓνℓ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_s \\rightarrow K \\ell \ u _\\ell $$\\end{document} decays. In particular we present results derived by applying either the Dispersive Matrix (DM) method of Di Carlo et al. (Phys Rev D 104:054502, 2021), Martinelli et al. (Phys Rev D 104:094512, 2021), Martinelli et al. (Phys Rev D 105:034503, 2022), Martinelli et al. (Eur Phys J C 82:1083, 2022), Martinelli et al. (JHEP 08:022, 2022) and Martinelli et al. (Phys Rev D 106:093002, 2022) or the more standard Boyd–Grinstein–Lebed (BGL) (Boyd et al. in Phys Rev D 56:6895, 1997) approach to the most recent values of the form factors determined in lattice QCD. Using all the available lattice results for the form factors from the DM method we get the theoretical value Rth(D∗)=0.262±0.009\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^{\ extrm{th}}(D^*) = 0.262 \\pm 0.009$$\\end{document} and we extract from a bin-per-bin analysis of the experimental data the value |Vcb|=(39.92±0.64)·10-3.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert = (39.92 \\pm 0.64) \\cdot 10^{-3}.$$\\end{document} Our result for R(D∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R(D^*)$$\\end{document} is consistent with the latest experimental world average Rexp(D∗)=0.284±0.012\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R^{\ extrm{exp}}(D^*) = 0.284 \\pm 0.012$$\\end{document} (HFLAV Collaboration in Preliminary average of R(D) and R(D∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R(D^*)$$\\end{document} as for Summer 2023. See https://hflav-eos.web.cern.ch/hflav-eos/semi/summer23/html/RDsDsstar/RDRDs.html) at the ≃1.5σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\simeq 1.5\\,\\sigma $$\\end{document} level. Our value for |Vcb|\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert $$\\end{document} is compatible with the latest inclusive determinations |Vcb|incl=(41.97±0.48)·10-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert ^{\ extrm{incl}} = (41.97 \\pm 0.48) \\cdot 10^{-3}$$\\end{document} (Finauri and Gambino in The q2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2$$\\end{document} moments in inclusive semileptonic B decays. arXiv:2310.20324) and |Vcb|incl=(41.69±0.63)·10-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{cb} \\vert ^{\ extrm{incl}} = (41.69\\pm 0.63) \\cdot 10^{-3}$$\\end{document} (Bernlochner et al. in JHEP 10:068, 2022) within ≃2.6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\simeq 2.6$$\\end{document} and ≃2.0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\simeq 2.0$$\\end{document} standard deviations, respectively. From a reappraisal of the calculations of |Vub|/|Vcb|,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{ub} \\vert / \\vert V_{cb} \\vert ,$$\\end{document} we also obtain |Vub|/|Vcb|=0.087±0.009\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{ub} \\vert / \\vert V_{cb} \\vert = 0.087\\pm 0.009$$\\end{document} in good agreement with the result |Vub|/|Vcb|=0.0844±0.0056\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\vert V_{ub} \\vert / \\vert V_{cb} \\vert = 0.0844\\pm 0.0056$$\\end{document} from the latest FLAG review (Flavour Lattice Averaging Group (FLAG) Collaboration in Phys J C 82:869, 2022).

Stability analysis of anisotropic stars in f(R, T) gravity through cracking technique

In this article, cracking technique is developed for spherically symmetric compact sources in the framework of f(R, T) gravity, where R denotes Ricci scalar and T stands for trace of energy momentum tensor. The characteristics of a star with anisotropic pressure stresses are investigated by utilizing the Tolman–Kuchowicz spacetime solutions. Modified field equations are developed for a particular model i.e., f(R,T)=R+2γT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f(R,T)=R+2\\gamma T$$\\end{document}, where γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} is constant, that are further used to develop expressions for matter density, radial and tangential pressures. A generalized form of the Tolman Oppenheimer Volkoff (TOV) equation is developed for the modified field equations. The consequence of the local density perturbation scheme, as presented by Biswas et al. (Eur Phys J C 80:175, 2020) is considered. The mathematical framework for cracking has been tested on five realistic stars namely, Vela X-1, Cen X-3, SMC X-1, PSR J1614-2230 and PSR J1903+327. The graph of forces distribution of these stars have been observed to check the stability regions. The results of cracking/overturning for various values of the parameters involved in this model are observed by checking the instability regions in the form intervals.

Compact stars with dark matter induced anisotropy in complexity-free background and effect of dark matter on GW echoes

ABSTRACT In this work, we consider the vanishing complexity factor scenario which has opened up a whole new way of generating solutions to the Einstein field equations for the spherically symmetric structure of celestial bodies. By using this very rare condition on the system of two metric potentials, viz. gtt and grr, we make reduce it to a uni-metric potential system satisfying all physical conditions. Along with this, we further have considered that the space–time is deformed by dark matter (DM) content in DM haloes resulting into perturbations in the gtt and grr metric potentials. This DM deformation is mathematically done by the complete geometric decoupling method where the decoupling parameter β decides the amount of DM content. In connection to the claimed post-merger object in the GW170817 event we have argued that if these compact stars were in galactic DM haloes with the assumption that the radius remains the same, the compactness factor can grow within the range 1/3 to 4/9 and therefore can generate gravitational waves (GW) echoes. Additionally, we have presented effect of β on the generation of GW echoes in accordance with the observational constraints related to the compact stars GW190814, PSR J0740+6620, PSR J1614−2230, Cen X-3, and LMC X-4.

Role of vanishing complexity factor in generating spherically symmetric gravitationally decoupled solution for self-gravitating compact object

In this work, we study the role of the vanishing complexity factor in generating self-gravitating compact objects under gravitational decoupling technique in f(Q)-gravity theory. To tackle the problem, the gravitationally decoupled action for modified f(Q) gravity has been adopted in the form {mathscr {S}}={{mathscr {S}}_{Q}}+{{mathscr {S}}^{*}_{theta }}, where {mathscr {S}}_Q denotes the Lagrangian density of the fields which appears in the f(Q) theory while {mathscr {S}}^{*}_{theta } (=alpha {mathscr {S}}_{theta }, where alpha is just a coupling parameter which controls the deformation) describes the Lagrangian density for a new kind of gravitational sector which has not been included in f(Q) gravity. After that, we developed an important relation between gravitational potentials via a systematic approach (Contreras and Stuchlik in Eur Phys J C 82:706, 2022) using the vanishing complexity factor condition in the context of f(Q) theory. We have used the Buchdahl model along with the mimic-to-density constraints approach for generating the complexity-free anisotropic solution. The qualitative physical analysis has been done along with the mass-radius relation for different compact objects via M-R curves to validate our solution. It is noticed that the coupling constant beta _1 has a definite impact on constraining the mass and radii of the object that are shown in M-R curves. The obtained results show that the compactness of the objects can be controlled by the coupling parameters.

Evolutionary behaviour of cosmological parameters with dynamical system analysis in f(Q, T) gravity

We have investigated the accelerating behaviour of the Universe in f(Q, T) gravity in an isotropic and homogeneous space-time. We have initially derive the dynamical parameters in the general form of f(Q,T)=alpha Q^m+beta T (Xu et al. in Eur Phys J C 79:708, 2019) and then split it into two cases (i) one with m=1 and the (ii) other with beta =0. In the first case, it reduces to the linear form of the functional f(Q, T) and second case leads to the higher power of the nonmetricity Q. In an assumed form of the hyperbolic scale factor, the models are constructed and its evolutionary behaviours are studied. The geometrical parameters as well the equation of state parameter are obtained and found to be in the preferred range of the cosmological observations. Marginal variation has been noticed in the behaviour of omega and omega _{eff} at present time. The violation of strong energy conditions in both the cases are shown. The dynamical system analysis for the models has been performed.

Comparison of finite element density functional with NWChem results for 18 molecules

Making use of the code presented in the previous work by Braun et al. (Eur Phys J B 92:230, 2019), finite element density functional calculations have been performed in Cartesian coordinates using the density functional approach for 18 mostly organic molecules, which are acetic acid, ammonia, benzene, butane, carbon-dioxide, ethane, ethanol, fluorine gas, iso-butane, methane, methanol, nitrogen gas, pentane, propane, urea, and water. The resulting total energies and densities were compared with those obtained using the Gaussian basis set package NWChem (Valiev et al. in Comput Phys Commun 181:1477, 2010) for a number of basis sets. We found very good agreement for the total energies and densities of the considered molecules using the two different approaches. This further highlights the success and usefulness of the finite element approach.

Interpolating matrix models for WLZZ series

We suggest a two-matrix model depending on three (infinite) sets of parameters which interpolates between all the models proposed in Wang et al. (Eur Phys J C 82:902, arXiv:2206.13038, 2022) and defined there through W-representations. We also discuss further generalizations of the WLZZ models, realized by W-representations associated with infinite commutative families of generators of w_infty -algebra which are presumably related to more sophisticated multi-matrix models. Integrable properties of these generalizations are described by what we call the skew hypergeometric tau -functions.

Anisotropic star by gravitational decoupling: A vanishing complexity approach

A new static spherically symmetric interior solution has been derived using Gravitational Decoupling via Complete Geometric Deformation, satisfying the vanishing complexity which explores the fundamental physical acceptability of the stellar model. In the current analysis, we present a systematic approach proposed by L. Herrera [Phys Rev D 97: 044010, 2018] and Contreras-Stuchlik [Eur Phys J C 82: 706, 2022] to derive a complexity-free solution. We plotted the graphical behavior of the energy density, radial pressure, tangential pressure, equation of state parameters, anisotropy, and stability analysis, respectively to check the physical viability of the complexity-free solution. In addition, we also discuss the energy exchange between the relativistic fluids which shows that the decoupling constant controls the direction of the energy exchange.

Chelating agents for the removal of calcareous deposits from archaeological ceramic materials. Compositional evaluation after immersion and physical gel application methods

The removal of calcareous deposits from archaeological ceramics is a very normal conservation-restoration treatment. Among the products used, chelating agents are quite common, including ethylenediaminetetraacetic acid salts (EDTA) (Berducou in La Conservation en archéologie: méthodes et pratique de la conservation-restauration des vestiges archéologiques, Masson, Paris, 1990; Buys and Oakley The conservation and restoration of ceramics, Butterworth-Heinemann, Oxford, 1993; Crisci et al. in Appl Phys A Mater Sci Process, 2010. https://doi.org/10.1155/2009/893528). Nevertheless, some studies have proved that they can cause damages on the ceramic pieces, regarding changes in their composition, such as dissolution of calcareous components and metallic oxides leaching (Gibson in Stud Conserv, 1971. https://doi.org/10.1155/2009/893528; Fernández and Seva Sautuola in Rev del Inst Prehist y Arqueol 9:471–982, 2003). As a consequence, their artistic values might also change. In spite of that, these products are nowadays still in use, meaning that the treatments might be changing the information that archaeological ceramics carry. However, from the 80 s onwards a more secure alternative to direct application methods based on thickening agents was developed. With the aim of analysing the degradation mechanisms that may take place after the cleaning treatments’ application, ceramic specimens with artificial calcareous deposits (Sáenz-Martínez et al. in Eur Phys J Plus 136:798, 2021) were treated with a low-concentrated solution of EDTA tetrasodium salt applied by immersion and thickened with xanthan gum powder (Vanzan® NF-C). Finally, the products from the cleaning treatments were neutralised, respectively, by immersion and by rinsing with deionized water. The composition of the ceramic samples was established before the growth of calcareous deposits and after the treatments, in order to determine their effectiveness and safety. According to the results, EDTA salt treatments, both by immersion and thickened, were effective regarding the removal of the calcareous deposits and did not modify the elemental and mineralogical original composition of the specimens (XRF, XRPD, TG-DSC). In addition, no gel residues were detected by FTIR-ATR.

Complexity-free solution generated by gravitational decoupling for anisotropic self-gravitating star in symmetric teleparallel f(Q)-gravity theory

In this work, we attempt to find an anisotropic solution for a compact star generated by gravitational decoupling in f(Q)-gravity theory having a null complexity factor. To do this, we initially derive the complexity factor condition in f(Q) gravity theory using the definition given by Herrera (Phys Rev D 97:044010, 2018) and then derived a bridge equation between gravitational potentials by assuming complexity factor to be zero (Contreras and Stuchlik in Eur Phys J C 82:706, 2022). Next, we obtain two systems of equations using the complete geometric deformation (CGD) approach. The first system of equations is assumed to be an isotropic system in f(Q)-gravity whose isotropic condition is similar to GR while the second system is dependent on deformation functions. The solution of the first system is obtained by Buchdahl’s spacetime geometry while the governing equations for the second system are solved through the mimic constraint approach along with vanishing complexity condition. The novelty of our work is to generalize the perfect fluid solution into an anisotropic domain in f(Q)-gravity theory with zero complexity for the first time. We present the solution’s analysis to test its physical viability. We exhibit that the existence of pressure anisotropy due to gravitational within the self-gravitating bounded object plays a vital role to stabilize the f(Q) gravity system. In addition, we show that the constant involved in the solution controls the direction of energy flow between the perfect fluid and generic fluid matter distributions.