Gravity Modes Research Articles

CMB spectrum in unified EFT of dark energy: scalar-tensor and vector-tensor theories

We study the cosmic microwave background (CMB) radiation in the unified description of the effective field theory (EFT) of dark energy that accommodates both scalar-tensor and vector-tensor theories. The boundaries of different classes of theories are universally parameterised by a new EFT parameter αV characterising the vectorial nature of dark energy and a set of consistency relations associated with the global/local shift symmetry. After implementing the equations of motion in a Boltzmann code, as a demonstration, we compute the CMB power spectrum based on the wCDM background with the EFT parameterisation of perturbations and a concrete Horndeski/generalised Proca theory. We show that the vectorial nature generically prevents modifications of gravity in the CMB spectrum. On the other hand, while the shift symmetry is less significant in the perturbation equations unless the background is close to the ΛCDM, it requires that the effective equation of state of dark energy is in the phantom region w DE<-1. The latter is particularly interesting in light of the latest result of the DESI+CMB combination as the observational verification of w DE>-1 can rule out shift-symmetric theories including vector-tensor theories in one shot.

Non-linear three-mode coupling of gravity modes in rotating slowly pulsating B stars

Context. Slowly pulsating B (SPB) stars display multi-periodic variability in the gravito-inertial mode regime with indications of non-linear resonances between modes. Several have undergone asteroseismic modeling in the past few years to infer their internal properties, but only in a linear setting. These stars rotate fast, so that rotation is typically included in the modeling by means of the traditional approximation of rotation (TAR). Aims. We aim to extend the set of tools available for asteroseismology, by describing time-independent (stationary) resonant non-linear coupling among three gravito-inertial modes within the TAR. Such coupling offers the opportunity to use mode amplitude ratios in the asteroseismic modeling process, instead of only relying on frequencies of linear eigenmodes, as has been done so far. Methods. Following observational detections, we derive expressions for the resonant stationary non-linear coupling between three gravito-inertial modes in rotating stars. We assess selection rules and stability domains for stationary solutions. We also predict non-linear frequencies and amplitude ratio observables that can be compared with their observed counterparts. Results. The non-linear frequency shifts of stationary couplings are negligible compared to typical frequency errors derived from observations. The theoretically predicted amplitude ratios of combination frequencies match with some of their observational counterparts in the SPB targets. Other, unexplained observed ratios could be linked to other saturation mechanisms, to interactions between different modes, or to different opacity gradients in the driving zone. Conclusions. For the purpose of asteroseismic modeling, our non-linear mode coupling formalism can explain some of the stationary amplitude ratios of observed resonant mode couplings in single SPB stars monitored during 4 years by the Kepler space telescope.

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.

Stability analysis of wormhole solutions in [formula omitted] gravity utilizing Karmarkar condition with radial dependent redshift function

In this work, we examine the properties of wormhole (WH) solutions in the context of modified f(Q) gravity. The shape function (ξS(r)) and redshift function (ζ(r)) are crucial in wormhole modeling since they determine the metric of a wormhole and define its attributes. The investigation provides the interaction between f(Q) gravity features and gravitational effects, guaranteeing insights into potential wormhole configurations. Subsequently, we have looked at the behavior of energy conditions and the fundamental properties of WHs. Additionally, the volume integral quantifier (V IQ) is addressed, providing insight into the quantity of exotic matter needed in the vicinity of the wormhole throat. Furthermore, the stability of the WH solutions in both cases is examined using the Tolman–Oppenheimer–Volkoff (TOV) equation where it is evident that both WH solutions meet the equilibrium requirements. Both cases ensures the real-world acceptability of WH solutions due to the rising nature of active gravitational mass (Mactive). Our findings contribute to the current discussion about alternative gravity theories and exotic spacetime geometries.

Thermodynamic features of AdS black holes within the rastall gravity and perfect fluid matter framework

In this study, we analyzed the impact of a perfect fluid on the phase transition of Anti-de Sitter (AdS) black holes within the Rastall gravitational background. Compared to similar studies in the literature, the findings of this work are highlighted by the determination of analytical expressions for critical points for charged and Kerr-Newman AdS black holes using approximated formulas for the horizon radius. An accurate analysis of these new analytical expressions allowed us to discover a new viable condition that relates the Rastall parameter κ λ to the equation of state parameter ω, expressed as: κλ=ω1+ω . Thanks to this new condition, we were able to reproduce all the analytical expressions of critical points calculated within the framework of Einsteinâs general relativity for two cases: a charged AdS black hole and a rotating AdS black hole. These findings suggest that Rastall gravity, considering this new condition, could serve as an alternative theory of gravitation to general relativity. The approximate expression of the horizon radius also enabled the exploration of the distinctiveness of fractional-order phase transitions in these AdS black holes. Furthermore, we calculated the critical exponents, offering insights into the behavior of crucial thermodynamic quantities near the inflection point. Examining how a perfect fluid influences phase transition reveals various critical behaviors, demonstrating that the variation in the phase transition depends on the intensity of the perfect fluid. Notably, this variation is portrayed by a linearly increasing trajectory with the escalation of this intensity.

KIC 4150611: A quadruply eclipsing heptuple star system with a g-mode period-spacing pattern. Eclipse modelling of the triple and spectroscopic analysis.

KIC 4150611 is a high-order multiple composed of a triple system.\ It comprises: (1) a F1V primary (Aa) that is eclipsed on a 94.2d period by a tight 1.52d binary composed of two dim K/M dwarfs (Ab1 and Ab2), which also eclipse each other; (2) an 8.65d eccentric, eclipsing binary composed of two G stars (Ba and Bb); and (3) another faint eclipsing binary composed of two stars of unknown spectral type (Ca and Cb). In addition to its many eclipses, the system is an SB3 spectroscopic multiple (Aa, Ba, and Bb), and the primary (Aa) is a hybrid pulsator that exhibits high amplitude pressure and gravity modes. In aggregate, this richness in physics offers an excellent opportunity to obtain a precise physical characterisation of some of the stars in this system. In this work we aim to characterise the F1V primary by modelling its complex eclipse geometry and disentangled stellar spectra in preparation for follow-up work that will focus on its pulsations. We employed a novel photometric analysis of the complicated eclipse geometry of Aa to obtain the orbital and stellar properties of the triple. We acquired 51 TRES spectra at the Fred L. Whipple Observatory, calculating radial velocities and orbital elements of Aa (SB1) and the B binary (SB2). These spectra and radial velocities were used to perform spectral disentangling for Aa, Ba, and Bb. Spectral modelling was applied to the disentangled spectrum of Aa to obtain atmospheric properties. From our eclipse modelling we obtain precise stellar properties of the triple, including the mass ratios ($M_ Aa /(M_ Ab1 +M_ Ab2 Ab1 /M_ Ab2 the separation ratio Aab /a_ Ab1Ab2 0.01$), orbital periods Aab Ab1Ab2 and stellar radii ( R R R Via radial velocity fitting and spectral disentangling, we find orbital elements for Aa, Ba, and Bb that are in excellent agreement with each other and with previous results in the literature. Spectral modelling on the disentangled spectrum of Aa provides constraints on the effective temperature eff K), surface gravity (log$(g) = 4.14 0.18$ dex), micro-turbulent velocity micro rotation velocity ($v i = 127 and metallicity M/H

Preliminary sensitivity study for a gravitational redshift measurement with China’s Lunar exploration project

General relativity (GR) is a highly successful theory that describes gravity as a geometric phenomenon. The gravitational redshift, a classic test of GR, can potentially be violated in alternative gravity theories, and experimental tests on this effect are crucial for our understanding of gravity. In this paper, considering the space-ground clock comparisons with free-space links, we discuss a high-precision Doppler cancellation-based measurement model for testing gravitational redshift. This model can effectively reduce various sources of error and noise, reducing the influences of the first-order Doppler effect, atmospheric delay, Shapiro delay, etc. China’s Lunar Exploration Project (CLEP) is proposed to equip the deep-space H maser with a daily stability of 2×10−15 , which provides an approach for testing gravitational redshift. Based on the simulation, we analyze the space-ground clock comparison experiments of the CLEP experiment, and simulation analysis demonstrates that under ideal condition of high-precision measurement of the onboard H-maser frequency offset and drift, the CLEP experiment may reach the uncertainty of 3.7×10−6 after a measurement session of 60 days. Our results demonstrate that if the issue of frequency offset and drift is solved, CLEP missions have a potential of testing the gravitational redshift with high accuracy.

The PTA Hellings and Downs correlation unmasked by symmetries

The Hellings and Downs correlation curve describes the correlation of the timing residuals from pairs of pulsars as a function of their angular separation on the sky and is a smoking-gun signature for the detection of an isotropic stochastic background of gravitational waves. We show that it can be easily obtained fromrealizing that Lorentz transformations are conformal transformationson the celestial sphere and from the conformal properties of the two-point correlation of the timing residuals. This result allows several generalizations, e.g. the calculation of the three-point correlator of the time residuals and the inclusion of additional polarization modes (vector and/or scalar) arising in alternativetheories of gravity.

Asteroseismology of the young open cluster NGC 2516

Context. Asteroseismic modelling of isolated stars presents significant challenges due to the difficulty in accurately determining stellar parameters, particularly the stellar age. These challenges can be overcome by observing stars in open clusters whose coeval members share an initial chemical composition. The light curves from the all-sky survey by the Transiting Exoplanet Survey Satellite (TESS) allow us to investigate and analyse stellar variations in clusters with an unprecedented level of detail for the first time. Aims. We aim to detect gravity-mode oscillations in the early-type main-sequence members of the young open cluster NGC 2516 to deduce their internal rotation rates. Methods. We selected the 301 member stars with no more than mild contamination as our sample. We analysed the full-frame image light curves, which provide nearly continuous observations in the first and third years of TESS monitoring. We also collected high-resolution spectra using the Fiber-fed Extended Range Optical Spectrograph for the g-mode pulsators, with the aim of assessing the Gaia effective temperatures and gravities and preparing for future seismic modelling. Results. By fitting the theoretical isochrones to the colour-magnitude diagram of a cluster, we determined an age of 102 ± 15 Myr and inferred that the extinction at 550 nm (A0) is 0.53 ± 0.04 mag. We identified 147 stars with surface-brightness modulations: 24 with gravity (g-)mode pulsations (γ Doradus or slowly pulsating B-type stars) and 35 with pressure (p-)mode pulsations (δ Sct stars). When sorted by colour index, the amplitude spectra of the δ Sct stars show a distinct ordering and reveal a discernible frequency-temperature relationship. The near-core rotation rates, measured from period spacing patterns in two slowly pulsating B-type (SPB) stars and nine γ Dor stars, reach up to 3 d−1. This is at the high end of the values found from Kepler data of field stars of similar variability type. The γ Dor stars of NGC 2516 have internal rotation rates as high as 50% of their critical value, whereas the SPB stars exhibit rotation rates close to their critical rate. Although the B-type stars are rotating rapidly, we did not find long-term brightness and colour variations in the mid-infrared, which suggests that there are no disc or shell formation events in our sample. We also discussed the results of our spectroscopic observations for the g-mode pulsators.

NEW TECHNOLOGIES FOR PROCESSING TAILINGS OF A COPPER PROCESSING PLANT FOR THE EXTRACTION OF PLATINOIDS

The most important task of the mining and metallurgical industry in the world is the development of technology for the processing of industrial waste from metallurgical industries. In the world, balance ores of precious metals are practically available. This issue develops the processing of man-made waste, refractory ores, off-balance and low-grade dumps. The article considers studies of the material and rational compositions of the tailings of a copper concentrating plant in the conditions of JSC Almalyk MMC, determines the optimal method for tailings enrichment with an increase in the content of precious metals in the concentrate, and enhances an unconventional new scheme for processing platinum group concentrates with the extraction of platinum, palladium, silver and high recovery gold. Based on the learned subjects and analysis of studies results, the authors concluded that the centrifugal concentration of platinoids from the composition of the tailings was achieved due to accurate determinations of the particle size in the tailings with the selection of intense gravity modes. Combined hydrometallurgical methods for purifying platinoids and gold from impurities using combinations of chemical solvents have been developed. As a result, the developed technologies have achieved the possibility of complex extraction of platinum group metals from the tailings of concentrating plants of copper production with high degrees, through extraction of all precious metals.

Damping Obliquities of Hot Jupiter Hosts by Resonance Locking

When orbiting hotter stars, hot Jupiters are often highly inclined relative to their host star equator planes. By contrast, hot Jupiters orbiting cooler stars are more aligned. Prior attempts to explain this correlation between stellar obliquity and effective temperature have proven problematic. We show how resonance locking—the coupling of the planet's orbit to a stellar gravity mode (g-mode)—can solve this mystery. Cooler stars with their radiative cores are more likely to be found with g-mode frequencies increased substantially by core hydrogen burning. Strong frequency evolution in resonance lock drives strong tidal evolution; locking to an axisymmetric g-mode damps semimajor axes, eccentricities, and, as we show for the first time, obliquities. Around cooler stars, hot Jupiters evolve into spin–orbit alignment and may avoid engulfment. Hotter stars lack radiative cores and therefore preserve congenital spin–orbit misalignments. We focus on resonance locks with axisymmetric modes, supplementing our technical results with simple physical interpretations, and show that nonaxisymmetric modes also damp obliquity. Outstanding issues regarding the dissipation of tidally excited modes and the disabling of resonance locks are discussed quantitatively.

NEW TECHNOLOGIES FOR PROCESSING TAILINGS OF A COPPER PROCESSING PLANT FOR THE EXTRACTION OF PLATINOIDS

The most important task of the mining and metallurgical industry in the world is the development of technology for the processing of industrial waste from metallurgical industries. In the world, balance ores of precious metals are practically available. This issue develops the processing of man-made waste, refractory ores, off-balance and low-grade dumps. The article considers studies of the material and rational compositions of the tailings of a copper concentrating plant in the conditions of JSC Almalyk MMC, determines the optimal method for tailings enrichment with an increase in the content of precious metals in the concentrate, and enhances an unconventional new scheme for processing platinum group concentrates with the extraction of platinum, palladium, silver and high recovery gold. Based on the learned subjects and analysis of studies results, the authors concluded that the centrifugal concentration of platinoids from the composition of the tailings was achieved due to accurate determinations of the particle size in the tailings with the selection of intense gravity modes. Combined hydrometallurgical methods for purifying platinoids and gold from impurities using combinations of chemical solvents have been developed. As a result, the developed technologies have achieved the possibility of complex extraction of platinum group metals from the tailings of concentrating plants of copper production with high degrees, through extraction of all precious metals.

Predictive Modeling for Microchannel Flow Boiling Heat Transfer under the Dual Effect of Gravity and Surface Modification

This paper investigates the heat transfer performance of flow boiling in microchannels under the dual effect of gravity and surface modification through both experimental studies and mechanistic analysis. Utilizing a test bench with microchannels featuring surfaces of varying wettability levels and adjustable flow directions, multiple experiments on R134-a flow boiling heat transfer under the effects of gravity and surface modification were conducted, resulting in 1220 sets of experimental data. The mass flux ranged from 735 kg/m2s to 1271 kg/m2s, and the heating heat flux density ranged from 9 × 103 W/m2 to 46 × 103 W/m2. The experimental results revealed the differences in the influence of different gravity and surface modification conditions on heat transfer performance. It was found that the heat transfer performance of super-hydrophilic surfaces in horizontal flow is optimal and more stable heat transfer performance is observed when gravity is aligned with the flow direction. And the impact of gravity and surface modification on heat transfer has been explained through mechanistic analysis. Therefore, two new dimensionless numbers, Fa and Conew, were introduced to characterize the dual effects of gravity and surface modification on heat transfer. A new heat transfer model was developed based on these effects, and the prediction error of the heat transfer coefficient was reduced by 12–15% compared to existing models, significantly improving the prediction accuracy and expanding its application scope. The applicability and accuracy of the new model were also validated with other experimental data.

Primordial Black Hole–Neutron Star Merger Rate in Modified Gravity

In this work, we investigate the merger rate of primordial black hole–neutron star (PBH-NS) binaries in two widely studied modified gravity (MG) models: Hu–Sawicki f(R) gravity and the normal branch of Dvali–Gabadadze–Porrati gravity. In our analysis, we take into account the effects of MG on the halo properties, including halo mass function, halo concentration parameter, halo density profile, and velocity dispersion of dark matter particles. We find that these MG models, due to their stronger gravitational field induced by an effective fifth force, predict enhanced merger rates compared to general relativity. This enhancement is found to be redshift-dependent and sensitive to model parameters and PBH mass and fraction. Assuming a PBH mass range of 5–50 M ⊙, we compare the predicted merger rate of PBH-NS binaries with those inferred from LIGO–Virgo–KAGRA observations of gravitational waves (GWs). We find that the merger rates obtained from MG models will be consistent with the GW observations if the abundance of PBHs is relatively large, with the exact amount depending on the MG model and its parameter values, as well as PBH mass. We also establish upper limits on the abundance of PBHs in these MG frameworks while comparing them with the existing non-GW constraints, which can potentially impose even more stringent constraints.

Wide binaries and modified gravity (MOG)

Wide binary stars are used to test the modified gravity called Scalar-Tensor-Vector Gravity or MOG. This theory is based on the additional gravitational degrees of freedom, the scalar field G = GN (1+α), where GN is Newton's constant, and the massive (spin-1 graviton) vector field ϕμ . The wide binaries have separations of 2–30 kAU. The MOG acceleration law, derived from the MOG field equations and equations of motion of a massive test particle for weak gravitational fields, depends on the enhanced gravitational constant G = GN (1+α) and the effective running mass μ. The magnitude of α depends on the physical length scale or averaging scale ℓ of the system. The modified MOG acceleration law for weak gravitational fields predicts that for the solar system and for the wide binary star systems gravitational dynamics follows Newton's law.

Probability distributions of initial rotation velocities and core-boundary mixing efficiencies of γ Doradus stars

Context. The theory of rotational and chemical evolution is incomplete, thereby limiting the accuracy of model-dependent stellar mass and age determinations. The γ Doradus (γ Dor) pulsators are excellent points of calibration for the current state-of-the-art stellar evolution models, as their gravity modes probe the physical conditions in the deep stellar interior. Yet, individual asteroseismic modelling of these stars is not always possible because of insufficient observed oscillation modes. Aims. This paper presents a novel method to derive distributions of the stellar mass, age, core-boundary mixing efficiency, and initial rotation rates for γ Dor stars. Methods. We computed a grid of rotating stellar evolution models covering the entire γ Dor instability strip. We then used the observed distributions of the luminosity, effective temperature, buoyancy travel time, and near-core rotation frequency of a sample of 539 stars to assign a statistical weight to each of our models. This weight is a measure of how likely the combination of a specific model is. We then computed weighted histograms to derive the most likely distributions of the fundamental stellar properties. Results. We find that the rotation frequency at zero-age main sequence follows a normal distribution, peaking at around 25% of the critical Keplerian rotation frequency. The probability-density function for extent of the core-boundary mixing zone, given by a factor of fCBM times the local pressure scale height (assuming an exponentially decaying parameterisation), decreases linearly with increasing fCBM. Conclusions. Converting the distribution of fractions of critical rotation at the zero-age main sequence to units of d−1, we find most F-type stars start the main sequence with a rotation frequency between 0.5 d−1 and 2 d−1. Regarding the core-boundary mixing efficiency, we find that it is generally weak in this mass regime.

Quazinormal modes and greybody factor of black hole surrounded by a quintessence in the S-V-T modified gravity as well as shadow

The purpose of this study is to investigate the quasinormal modes (QNMs), greybody factors (GFs) and shadows in a plasma of a black hole (BH) surrounded by an exotic fluid of quintessence type in a scalar-vector-tensor modified gravity. The effects of a quintessence scalar field and the modified gravity (MOG) field on the QNM, GF, and shadow are examined. Using the sixth-order WKB approach, we investigate the QNMs of massless scalar and electromagnetic perturbations. Our findings show that as the quintessence and the MOG parameter (ϵ and α) increase, the oscillation frequencies decrease significantly. Gravitational wave damping, on the other hand, decreases with increasing ϵ and α. In addition, we obtain an analytical solution for the transmission coefficients (GF) and demonstrate that more thermal radiation reaches the observer at spatial infinity as both the ϵ and α parameters increase. We also investigate the effect of the plasma background on the BH shadow and show that as the plasma background parameter increases, the shadow radius slightly shrinks. Nevertheless, the shadow radius increases as α and ϵ increase. Particularly intriguing is the fact that increasing ϵ has a greater impact on the shadow radius than increasing α, indicating that the quintessence parameter has a greater impact than the MOG parameter.

Hawking Radiation as a Manifestation of Spontaneous Symmetry Breaking

We demonstrate that black hole evaporation can be modeled as a process where one symmetry of the system is spontaneously broken continuously. We then identify three free parameters of the system. The sign of one of the free parameters governs whether the particles emitted by the black hole are fermions or bosons. The present model explains why the black hole evaporation process is so universal. Interestingly, this universality emerges naturally inside certain modifications of gravity.

The dynamics of matter bounce cosmology in Weyl-type [formula omitted] gravity

In this work, we investigate the dynamics of bouncing cosmologies within the framework of Weyl-type f(Q,T) gravity. Here, Q represents the non-metricity of the space–time, is determined by the vector field wμ, while T represents the trace of the matter energy–momentum tensor. Our objective is to explore the feasibility of avoiding the Big Bang singularity by implementing a matter-bounce cosmology. To achieve this, we consider a specific model with the functional form f(Q,T)=αQ+β6κ2T, where α and β are model parameters. We analyze the dynamical parameters associated with this model and examine the influence of the Weyl-type f(Q,T) theory on these parameters. Moreover, we assess the stability of the proposed model to ensure its viability as a cosmological scenario. Through our analysis, we aim to gain insights into the potential implications and consequences of Weyl-type f(Q,T) gravity for bouncing scenarios, contributing to our understanding of alternative gravitational theories in the context of cosmology.

Bayesian deep learning for cosmic volumes with modified gravity

Context. The new generation of galaxy surveys will provide unprecedented data that will allow us to test gravity deviations at cosmological scales at a much higher precision than could be achieved previously. A robust cosmological analysis of the large-scale structure demands exploiting the nonlinear information encoded in the cosmic web. Machine-learning techniques provide these tools, but no a priori assessment of the uncertainties. Aims. We extract cosmological parameters from modified gravity (MG) simulations through deep neural networks that include uncertainty estimations. Methods. We implemented Bayesian neural networks (BNNs) with an enriched approximate posterior distribution considering two cases: the first case with a single Bayesian last layer (BLL), and the other case with Bayesian layers at all levels (FullB). We trained both BNNs with real-space density fields and power spectra from a suite of 2000 dark matter-only particle-mesh N-body simulations including MG models relying on MG-PICOLA, covering 256 h−1 Mpc side cubical volumes with 1283 particles. Results. BNNs excel in accurately predicting parameters for Ωm and σ8 and their respective correlation with the MG parameter. Furthermore, we find that BNNs yield well-calibrated uncertainty estimates that overcome the over- and under-estimation issues in traditional neural networks. The MG parameter leads to a significant degeneracy, and σ8 might be one possible explanation of the poor MG predictions. Ignoring MG, we obtain a deviation of the relative errors in Ωm and σ8 by 30% at least. Moreover, we report consistent results from the density field and power spectrum analysis and comparable results between BLL and FullB experiments. This halved the computing time. This work contributes to preparing the path for extracting cosmological parameters from complete small cosmic volumes towards the highly nonlinear regime.