Gravity Corrections Research Articles

Resurgence in Lorentzian quantum cosmology: No-boundary saddles and resummation of quantum gravity corrections around tunneling saddle points

Resurgence in Lorentzian quantum cosmology: No-boundary saddles and resummation of quantum gravity corrections around tunneling saddle points

Heptaminol hair testing to highlight octodrine contamination in supplements, responsible for a doping adverse analytical finding

Octodrine, also known as dimethylhexylamine (DMHA), is a central nervous stimulant. When ingested by humans, octodrine is rapidly metabolized to heptaminol, the main compound present in the blood. Due to their stimulant activities, octodrine and its metabolite are specified substances in section S6b “specified stimulants” of the World Anti-Doping Agency (WADA) Prohibited List, prohibited in competition. But in some cases, they can be responsible for an adverse analytical finding (AAF) following contamination, with a low concentration in the urine. In such cases, a hair test can distinguish doping from contamination according to the concentration measured, or the absence of the target drug. However, no data are available in the literature. The aim of this study was to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of octodrine and heptaminol in hair, and to apply it to an athlete with an AAF with heptaminol (141 and 136 ng/mL in urine samples A and B after correction for specific gravity) and octodrine (16 ng/mL, not given by the WADA laboratory in sample A as being below the minimum request level of 50 ng/mL).All the supplements taken by the athlete were analysed, and pubic hair (black, 1.5–2 cm long, no head hair available) and toenail clippings (0.1 cm) were sampled two months after AAF. A supplement was identified as the source of contamination, containing octodrine at a concentration range 16–34 µg/g. The athlete had taken 13 g daily (0.2–0.4 mg octodrine) for 20 days prior to the AAF (total dose 4–8 mg). His pubic hair and toenail clippings contained only heptaminol (30 pg/mg and 3 pg/mg, respectively). A controlled study was carried out on a volunteer who took a single 13 g dose of the contaminated supplement (single dose of octodrine 0.2–0.4 mg). His urine was positive for both compounds, with concentrations very close to those of the athlete on the day of the AAF after the same delay between intake and sampling (around 4 h). One month later, his head hair and pubic hair showed only heptaminol at 2 and 3 pg/mg, respectively, and toenail clippings were totally negative for both compounds. The contamination was accepted by the WADA commission, but the athlete was still banned for 9 months for having consumed supplements purchased on the internet.

The shadow and gamma-ray bursts of a Schwarzschild black hole in asymptotic safety

Abstract The effects and rules of the dimensionless parameter $\xi$ on neutrino annihilation $\nu+\bar{\nu}\to e^{-}+e^{+}$ dominated gamma-ray bursts are analysed and investigated within the context of black holes in asymptotic safety. We also computationally model photon orbits around black holes, as photons and neutrinos have the same geodesic equations near black holes. We show that the black hole shadow radius decreases with increasing $\xi$. Calculations are made to determine the temperature of the accretion disk surrounding the black hole and the ratio $\dot{Q}/\dot{Q}_{Newt}$ of energy deposition per unit time to that of the Newtonian scenario. The accretion disk temperature peaks at a higher temperature due to quantum gravity corrections, which increases the probability of neutrino emission from the black hole. It is interesting to note that larger quantum gravity effects cause the ratio value to significantly decline. In the neutrino-antineutrino annihilation process, the energy deposition rate is sufficient even while the energy conversion is inhibited because of quantum corrections. Gamma-ray bursts might originate from the corrected annihilation process. Additionally, we examine the derivative $\mathrm{d}\dot{Q}/\mathrm{d}r$ about the star radius $r$. The findings demonstrate that the ratio is lowered by the black hole's quantum influence. The neutrino pair annihilation grows weaker the more prominent the influence of quantum gravity is.

Ultraviolet finite resummation of perturbative quantum gravity

Abstract If the metric is chosen to depend exponentially on the conformal factor, and if one works in a gauge where the conformal factor has the wrong sign propagator, perturbative quantum gravity corrections can be partially resummed into a series of terms each of which is ultraviolet finite. These new terms however are not perturbative in some small parameter, and are not individually BRST invariant, or background diffeomorphism invariant. With appropriate parametrisation, the finiteness property holds true also for a full phenomenologically relevant theory of quantum gravity coupled to (beyond the standard model) matter fields, provided massive tadpole corrections are set to zero by a trivial renormalisation.

Quantum Gravity Corrections to the Inflationary Spectrum in a Bohmian Approach

A precise interpretation of the universe wave function is forbidden in the spirit of the Copenhagen School since a precise notion of measure operation cannot be satisfactorily defined. Here, we propose a Bohmian interpretation of the isotropic universe quantum dynamics, in which the Hamilton–Jacobi equation is restated by including quantum corrections, which lead to a classical trajectory containing effects of order ℏ2. This solution is then used to determine the spectrum of gauge-invariant quantum fluctuations living on the obtained background model. The analysis is performed adopting the wave function approach to describe the fluctuation dynamics, which gives a time-dependent harmonic oscillator for each Fourier mode and whose frequency is affected by the ℏ2 corrections. The properties of the emerging spectrum are discussed, outlining the modification induced with respect to the scale-invariant result, and the hierarchy of the spectral index running is discussed.

Determination of the Topography-Bounded Atmospheric Gravity Correction for the Area of Poland

Determination of the Topography-Bounded Atmospheric Gravity Correction for the Area of Poland

Generalized covariant entropy bound in Einstein gravity with quadratic curvature corrections

We explore the generalized covariant entropy bound in the theory where Einstein gravity is perturbed by quadratic curvature terms, which can be viewed as the first-order quantum correction to Einstein gravity. By replacing the Bekenstein-Hawking entropy with the holographic entanglement entropy of this theory and introducing two reasonable physical assumptions, we demonstrate that the corresponding Generalized Covariant Entropy Bound is satisfied under a first-order approximation of the perturbation from the quadratic curvature terms. Our findings suggest that the entropy bound and the Generalized Second Law of black holes are satisfied in the Einstein gravity under the first-order perturbation from the quadratic curvature corrections, and they also imply that the generalized covariant entropy bound may still hold even after considering the quantum correction of gravity, but in this case, we may need to use holographic entanglement entropy as the formula for gravitational entropy.

Can nonlocal gravity really explain dark energy?

In view to scrutinize the idea that nonlocal modifications of General Relativity could dynamically address the dark energy problem, we investigate the evolution of the Universe at infrared scales as an Infinite Derivative Gravity model of the Ricci scalar, without introducing the cosmological constant Λ or any scalar field. The accelerated expansion of the late Universe is shown to be compatible with the emergence of nonlocal gravitational effects at sufficiently low energies. A technique for circumventing the mathematical complexity of the nonlocal cosmological equations is developed and, after drawing a connection with the Starobinsky gravity, verifiable predictions are considered, like a possible decreasing in the strength of the effective gravitational constant. In conclusion, the emergence of nonlocal gravity corrections at given scales could be an efficient mechanism to address the dark energy problem.

On the entropy corrected thermal features of black holes

In this work, we investigate the thermal properties of black holes using a new class of generalized entropy functions [K Ourabah, Class. Quantum Grav., 41, 015 010 (2024)]. At the fundamental level, these entropic forms are associated with alternative gravitational laws, within an entropic gravity framework. Our investigation revolves around three distinct entropy functions associated with the Yukawa Potential Correction, Non-local Gravity Correction, and Gradient Field Gravity Correction. Through comparative analysis, we study how such entropic constructs impact the thermodynamic behavior of black holes. For each case, we derive the stability thermodynamic conditions associated with the respective entropic constructs.

Dark energy as a critical period in binary motion: Bounds from multi-scale binaries

We study the two-body problem in the context of both dark energy and post-Newtonian modifications. In this unified framework, we demonstrate that dark energy plays the role of a critical period with TΛ = 2π/c√Λ ≈ 60 Gyr. We also show that the ratio between the orbital and critical periods naturally emerges from the Kretschmann scalar, which is a quadratic curvature invariant characterizing all binary systems effectively represented by de Sitter-Schwarzschild space-time. The suitability of a binary system in constraining dark energy is determined by the ratio between its Keplerian orbital period, TK, and the critical period, TΛ. Systems with TK ≈ TΛ are optimal for constraining the cosmological constant, Λ, such as the Local Group and the Virgo Cluster. Systems with TK ≪ TΛ are dominated by attractive gravity (which are best suited for studying modified gravity corrections). Systems with TK ≫ TΛ are dominated by repulsive dark energy and can thus be used to constrain Λ from below. We used our unified framework of post-Newtonian and dark-energy modifications to calculate the precession of bounded and unbounded astrophysical systems and infer constraints on Λ from them. We analyzed pulsars, the solar system, S stars around Sgr A*, the Local Group, and the Virgo Cluster, having orbital periods of days to gigayears. Our results reveal that the upper bound on the cosmological constant decreases when the orbital period of the system increases, emphasizing that Λ is a critical period in binary motion.

Entanglement degradation as a tool to detect signatures of modified gravity

We investigate entanglement degradation in the vicinity of a quantum corrected black hole. We consider a biprtite system (Alice-Rob) with Alice freely falling (radially) into the event horizon of a quantum corrected black hole and Rob being in the vicinity of the event horizon of the black hole. We consider a maximally entangled state (in the Fock basis) and start with the basic assumption that Rob is an uniformly accelerated observer. We then give a pedagogical analysis of the relation involving the Minkowski vaccum state and Rindler number states. Following the analogy given in Martín-Martínez [], we establish the relation between the Hartle-Hawking vacuum state and Boulware and anti-Bouware number states from the Minkowski-Rindler relation. We then write down the quantum corrected black hole metric by making use of the near horizon approximation in an appropriate form. Next, we obtain the analytical forms of logarithmic negativity and mutual information and plot as a function of Rob’s distance from the r=0 point. We observe that the entanglement degradation slows down because of the structural change in the lapse function of the metric via the incorporation of quantum gravity corrections in the Schwarzschild black hole. It is crucial to understand that any modified gravity theories that changes the metric structure results in a different rate of degradation of the entanglement. At the horizon radius, the entanglement degradation is always complete irrespective of the underlying theory. This observation may lead to the identification of the signature of modified gravity theories in a future generation of advanced observational scenarios. Such a modification can come from higher curvature corrections, higher dimensional gravity theories, quantum gravity corrections, etc. We can also interpret this effect as a noisy quantum channel with an operator sum representation of a completely positive and trace preserving map. We then finally obtain the entanglement fidelity using this operator sum representation. Published by the American Physical Society 2024

On the degrees of freedom of R2 gravity in flat spacetime

We study the degrees of freedom of R2 gravity in flat spacetime with two approaches. By rewriting the theory a la Stueckelberg, and implementing Lorentz-like gauges to the metric perturbations, we confirm that the pure theory propagates one scalar degree of freedom, while the full theory contains two tensor modes in addition. We then consider the degrees of freedom by directly examining the metric perturbations. We show that the degrees of freedom of the full theory match with those obtained with the manifestly covariant approach. In contrast, we find that the pure R2 gravity has no degrees of freedom. We show that a similar discrepancy between the two approaches appears also in a theory dual to the three-form, and appears due to the Lorentz-like gauges, which lead to the fictitious modes even after the residual gauge redundancy has been taken into account. At first sight, this implies a discontinuity between the full theory and the pure case. By studying the first-order corrections of the full R2 gravity beyond the linear regime, we show that at high-energies, both scalar and tensor degrees of freedom become strongly coupled. This implies that the apparent discontinuity of pure and full R2 gravity is just an artefact of the perturbation theory, and further supports the absence of degrees of freedom in the pure R2 gravity.

A Atmospheric Correction of FG5 Absolute Gravimetry Data using Measured Air Pressure

Changes in atmospheric density affect atmospheric pressure, which is a key factor affecting high-precision gravity measurement. Currently, atmospheric correction of absolute gravity measurements uses the empirical admittance value recommended by the International Association of Geodesy (−0.3 μGal/mbar); however, the actual admittance value changes with atmospheric mass and time. In this study, we determine the effect of using measured admittance values for absolute gravity correction. First, high-precision relative gravimeters (GWR OSG-057, Scintrex CG5) are used for continuous gravity measurements. Then, air pressure measured by the pressure sensor equipped by FG5 absolute gravimeter is used to obtain the atmospheric admittance using the iterative least squares method, which is compared with the theoretical atmospheric admittance. Taking FG5-257 as an example, we use the measured admittance for atmospheric correction of absolute gravity at four different elevations (Lhasa, Nagqu, Gar, and Suining, China). The results are as follows: 1) According to co-location measurements in Lhasa, CG5 and OSG gravimeter measured admittance values exhibit comparable precision (–0.332 ± 0.003 μGal/mbar and –0.332 ± 0.001 μGal/mbar, respectively), though the CG5 has larger standard deviation. 2) After correction using the measured admittance, changes in set standard deviation and measurement precision are approximately 0.01 μGal; however, the effect on the measurement results does not exceed 1 μGal, which is equivalent to the measurement precision of FG5. Therefore, measured admittance values are only recommended for atmospheric correction of high-precision absolute gravity measurements.

Effect of prenatal exposure to phthalates on birth weight of offspring: A meta-analysis

Prenatal exposure to phthalates is common. However, its effect on birth weight has always been met with conflicting conclusions. To explore the effects of prenatal phthalate exposure on neonatal weight, we searched PubMed, Web of Science (WOS), Cochrane Library, and Embase databases for articles published up to October 24, 2023. Observational studies with 95% confidence intervals (CI) were included. Our findings indicate no significant association between either mixed exposure effects or single phthalate metabolites and offspring birth weight when monitoring maternal urine phthalate metabolites. When stratified by sex, ΣHMWPs and MMP significantly reduced the birth weight of female offspring (ΣHMWPs: Pooled β = −62.08, 95%CI: −123.11 to −1.05, P = 0.046; MMP: Pooled β = −10.77, 95%CI: −18.74 to −2.80, P = 0.008). The results of subgroup analysis showed that ΣPAEs and ΣDEHP significantly decreased birth weight in the specific gravity correction group (ΣPAEs: Pooled estimates = −29.31, 95%CI: −58.52 to −0.10, P = 0.049; ΣDEHP: Pooled estimates = −18.25, 95%CI: −33.03 to −3.47, P = 0.016), and MECPP showed a positive correlation in the creatinine correction group (MECPP: Pooled estimates = 18.45, 95%CI: 0.13 to 36.77, P = 0.048). MEP and MBzP were negatively associated with birth weight in the no adjustment for gestational age group (MEP: Pooled estimates = −7.70, 95%CI: −14.19 to −1.21, P = 0.020; MBzP: Pooled estimates = −9.55, 95%CI: −16.08 to −3.03, P = 0.004). To make the results more convincing, more high-quality studies with large samples are urgently required.

Cosmic background neutrinos deflected by gravity: DEMNUni simulation analysis

The local supercluster acts as a gravity deflection source for cosmic background neutrinos. This deflection by gravity changes the neutrino helicity and therefore has important consequences for ground based tritium capture experiments aimed at determining if the neutrino is Dirac or Majorana. Here we explore the deflection effect of the local supercluster using two simulations from the DEMNUni suite characterised by very different mass resolutions, as they are both filled with 20483 dark matter particles (and an equal number of massive neutrino particles) but have comoving volumes of (2 h -1Gpc)3 and (500 h -1Mpc)3, respectively. We reaffirm our previous results and show that the lightest neutrinos are ultra-relativistic enough to suffer little deflection by gravity and at the same time not relativistic enough to achieve the same capture rate for Dirac and Majorana cases. This means that the capture rate in Ptolemy-like experiments will be sensitive to the neutrino nature and that gravity deflection enlarges the difference between Majorana and Dirac rates. Moreover, using the relation between mass and momentum of the neutrinos frozen Fermi-Dirac distribution, but taking into consideration gravity corrections, we are able to calculate the deflection angle for different neutrino masses from the same set of neutrinos obtained from the simulation. Doing so, we provide a formula to compute the deflection angle for any neutrino mass, such that when cosmology detects an absolute neutrino mass, precise predictions can be made for tritium ground-based detectors on Earth aimed to determine neutrinos nature.

Shadow and photon ring of black hole in asymptotically safe gravity

In this paper, we discuss the influence of thin disk accretion and asymptotically safe (AS) gravity correction parameters on the shadow and photon ring of black hole. For the thin disk accretion, the dark region is the shadow of the black hole, and the bright photon ring is composed of direct image, lensing ring, and photon ring. For the specific intensity of the radiation source of the accretion disk, we consider three different emission profile models. For the second-order attenuation function model in which the emission starts from the innermost circular orbit, direct image, lensing ring, and photon ring can be clearly distinguished. The direct image contributes most of the brightness, and the lensing ring contributes a small portion, while the contribution of the photon ring can almost be ignored. And the observed corresponding intensity peak decreases with the increase of the AS gravity parameter, that is, the corresponding brightness of the photon ring darkens as correction parameter increases. For the third-order attenuation function model in which the emission begins at the radius of the photon sphere, lensing ring and photon ring are superimposed on the direct radiation. Thus a new extreme value of the observed intensity emerges, and the extreme value increases with the increase of the AS gravity parameter, which leads to a brighter observed photon ring. For the anti-trigonometric attenuation function model in which the radiation starts from the event horizon, the superposition range of lensing ring and photon ring on the direct radiation becomes larger, which makes photon ring wider. The smaller the AS gravity parameter, the more difficult it is to distinguish between the lensing ring and photon ring, and the brighter the photon ring turns. In short, the results show that the shadow radius decreases with the increase of the AS correction parameter. For different AS gravity correction parameters, the light intensities of emission source, especially emission profiles of the observed intensity are significantly different, resulting in obvious differences in observed emission intensity between the shadow of the black hole and the bright photon ring of the black hole.

Thermodynamic topology of black holes from bulk-boundary, extended, and restricted phase space perspectives

In this article, we investigate the thermodynamic topology of some black holes, namely AdS Reissner Nordstrom (R–N), AdS Einstein–Gauss–Bonnet (EGB), and AdS Einstein-power-Yang–Mills (EPYM), from different frameworks: bulk-boundary (BB) and restricted phase space (RPS). Using the generalized off-shell Helmholtz free energy method, we calculate the thermodynamic topology of the selected black holes in each space separately and determine their topological classifications. We show that the addition of GB terms, dimensions, and other factors do not affect the topological classes of black holes in both spaces. The calculations and plots indicate that the AdS R–N and AdS EGB black holes show similar behavior and their topological numbers sets in both spaces, i.e., BB and RPS, are similar and equal to (W=+1). However, AdS EPYM black holes show an interesting behavior. In addition to BBT and RPS, we also consider the extended phase space thermodynamics (EPST) and evaluate the thermodynamic topology for AdS EPYM black hole. The changing (r−τ) in both spaces shows similar behavior. Also, the topological number and the total topological numbers for this black hole in the BB, RPS and EPS thermodynamics are completely same, i,e., (ωBBT=ωRPS=ωEPST=+1,−1) or WBBT=WRPS=WEPST=0. An important point is that the Einstein–Yang–Mills black hole has thermodynamic topology equivalence in three spaces. The present result may be due to the non-linear YM charge parameter and the difference between the gauge and gravity corrections in the above black holes.

Perturbed solutions in matter FLRW model with R μ ν R μ ν and R 4 gravity

In this paper, we consider the R μ ν R μ ν and R 4 gravity corrections to the general relativity (GR)-based cosmological model, and then apply the perturbation theory to first order to explore the effects of these corrections on the results obtained from the GR-based cosmological model. This cosmological model suggests a small nonzero value (∼10−3) of the equation of State (EoS) parameter (w) of the matter field. We calculate the Hubble parameter and the deceleration parameter using the perturbed solutions of the scale factor, which are in very good agreement with the recent observational data. Additionally, we also explore the validity of the generalized second law of thermodynamics under the R μ ν R μ ν and R 4 gravity theories.

Holographic codes from hyperinvariant tensor networks

Holographic quantum-error correcting codes are models of bulk/boundary dualities such as the anti-de Sitter/conformal field theory (AdS/CFT) correspondence, where a higher-dimensional bulk geometry is associated with the code’s logical degrees of freedom. Previous discrete holographic codes based on tensor networks have reproduced the general code properties expected from continuum AdS/CFT, such as complementary recovery. However, the boundary states of such tensor networks typically do not exhibit the expected correlation functions of CFT boundary states. In this work, we show that a new class of exact holographic codes, extending the previously proposed hyperinvariant tensor networks into quantum codes, produce the correct boundary correlation functions. This approach yields a dictionary between logical states in the bulk and the critical renormalization group flow of boundary states. Furthermore, these codes exhibit a state-dependent breakdown of complementary recovery as expected from AdS/CFT under small quantum gravity corrections.

Sensitivity of gravity anomalies to mantle rheology at mid-ocean ridge – transform fault systems

Marine gravity data can provide information on the distribution of mass anomalies in the oceanic crust and upper mantle. Computing corresponding gravity anomalies, especially so-called ‘residual’ gravity anomalies that directly reflect variations in the crustal structure, relies on gravity corrections of both seafloor relief and lithospheric thermal structure. The lithospheric thermal gravity correction involves either a plate cooling approximation or a mantle flow model with the latter typically done using simplified assumptions on mantle rheology. However, a detailed study of how differing rheological models affect the computed gravity anomalies is still missing. Here, we systematically examine the differences in residual mantle Bouguer anomalies (RMBA) caused by differing assumptions on mantle rheology for 16 mid-ocean ridge – transform fault systems. Our calculations show that isoviscous models tend to underpredict RMBA values within the transform deformation zone and overpredict them in the far field at older plate ages, when compared to plate cooling and nonlinear viscoplastic models. This discrepancy stems from isoviscous models failing to capture plate-like deformation, as well as their inability to resolve brittle failure and the associated strain localization that leads to warm upwelling beneath the transform fault. By exploring a wide parameter range, we find that the importance of mantle rheology scales with plate tectonic parameters at the mid-ocean ridge – transform fault system such as transform age offset, spreading rate, and transform fault length. These findings suggest that gravity thermal corrections at the intrinsically three-dimensional ridge – transform systems should employ mantle flow models that resolve plate-like deformation and brittle failure.