Testing the Kerr black hole hypothesis with the continuum-fitting and the iron line methods: the case of GRS 1915+105

The continuum-fitting and the iron line methods are currently the two leading techniques for probing the strong gravity region around accreting black holes. In the present work, we test the Kerr black hole hypothesis with the stellar-mass black hole in GRS 1915+105 by analyzing five disk-dominated RXTE spectra and one reflection-dominated Suzaku spectrum. The combination of the constraints from the continuum-fitting and the iron line methods has the potential to provide more stringent tests of the Kerr metric. Our constraint on the Johannsen deformation parameter α13 is -0.15 < α13 < 0.14 at 3σ, where the Kerr metric is recovered when α13 = 0.

Primordial big bang nucleosynthesis and generalized uncertainty principle

The Generalized Uncertainty Principle (GUP) naturally emerges in several quantum gravity models, predicting the existence of a minimal length at Planck scale. Here, we consider the quadratic GUP as a semiclassical approach to thermodynamic gravity and constrain the deformation parameter by using observational bounds from Big Bang Nucleosynthesis and primordial abundances of the light elements $${}^4 He, D, {}^7 Li$$ 4 H e , D , 7 L i . We show that our result fits with most of existing bounds on $$\beta $$ β derived from other cosmological studies.

Blandford-Znajek mechanism in the general stationary axially-symmetric black-hole spacetime

We consider the Blandford-Znajek process of electromagnetic extraction of energy from a general axially symmetric asymptotically flat slowly rotating black hole. Using the general parametrization of the black-hole spacetime we construct formulas for the flux of the magnetic field and the rate of energy extraction, which are valid not only for the Kerr spacetime, but also for its arbitrary axially symmetric deformations. We show that in the dominant order these quantities depend only on a single deformation parameter, which relates the spin frequency of a black hole with its rotation parameter.

Interplay between Spacetime Curvature, Speed of Light and Quantum Deformations of Relativistic Symmetries

Recent work showed that κ-deformations can describe the quantum deformation of several relativistic models that have been proposed in the context of quantum gravity phenomenology. Starting from the Poincaré algebra of special-relativistic symmetries, one can toggle the curvature parameter Λ, the Planck scale quantum deformation parameter κ and the speed of light parameter c to move to the well-studied κ-Poincaré algebra, the (quantum) (A)dS algebra, the (quantum) Galilei and Carroll algebras and their curved versions. In this review, we survey the properties and relations of these algebras of relativistic symmetries and their associated noncommutative spacetimes, emphasizing the nontrivial effects of interplay between curvature, quantum deformation and speed of light parameters.

Embeddings of integrable models in supergravity and their perturbative stability

We discuss the perturbative stability of an AdS 3 non-supersymmetric solution of the type-IIB supergravity, whose internal geometry is given by the direct product of a round three-sphere and two λ-deformed factors based on the coset CFTs SU(2)/U(1) and SL(2, ℝ)/SO(1,1). This solution admits a two-dimensional parametric space spanned by the inverse radius of the AdS 3 and the deformation parameter λ. Reality of the background imposes restrictions on the values of these parameters. Further limitations on the values of the inverse radius and the parameter λ arise after requiring the stability of the solution. Our approach relies on the study of scalar perturbations around the AdS 3 vacuum of a three-dimensional effective theory. This reveals the existence of a region in the parametric space where the Breitenlohner-Freedman bound is not violated.

Polaritonic crystal formed of a tunnel-coupled microcavity array and an ensemble of quantum dots

Propagation of polariton excitations in a defect-containing one-dimensional lattice of microcavities with embedded ultracold atomic nanoclusters (quantum dots) is being considered. The virtual crystal approximation is used to study the properties of electromagnetic excitation spectrum resulting from random variations of the atomic subsystem composition and positions of micropores, as well as from a homogeneous elastic deformation of the considered one-dimensional structure. The group velocity dependence of polariton excitations on structural defect concentration and on deformation parameter is being numerically modeled.

Ejection fraction basal strain ratio (EFBSR), a new accurate echocardiographic deformation parameter to screen cardiac amyloidosis among hypertrophic cardiopathies

Background Early diagnosis of cardiac amyloidosis (CA) is challenging. Several echocardiographic (echo) parameters have been proposed to differentiate CA from hypertrophic cardiomyopathy (HCM), but their respective value is debated. CA is known to be characterized by a more severe decline in longitudinal deformation parameters as compared with radial function parameters (LVEF). This characteristic justified the use of the ejection fraction strain ratio (EFSR) in these patients. However, since longitudinal dysfunction usually predominates in basal segments (apical sparing), we postulated that a new parameter focusing on LVEF and basal LV deformation (EFBSR: ejection fraction basal strain ratio) will even better discriminate patients with CA from HCM than EFSR and other echo or strain parameters. Purpose To compare the accuracy of deformation-based echocardiographic parameters for detecting CA in a population with different causes of LV hypertrophy. Methods and results We included 237 subjects, of which 89 patients with CA (77±10.7 years, 72% male, EF: 56.2±12.8%, and mean interventricular septum: 18.3±3.5 mm), 137 patients with hypertrophic cardiomyopathies (HCM), 52 patients with severe aortic stenosis with myocardial remodeling, 20 patients with arterial hypertension, and 20 control patients. Conventional echocardiographic parameters and strain-derived ratios (Relative apical sparing (RELAPS), Ejection Fraction Strain Ratio (EFSR) and EFBSR) were analyzed. EFBSR and RELAPS presented with the best performance to discriminate CA from other causes of hypertrophy (Area Under the Curve (AUC): 0.880; 95% CI: 0.830–0.929 and 0.903; 95% CI: 0.863–0.943 respectively) (p-value=0.3). In our study, among all the parameters, RELAPS had the best specificity (89.8% vs 88.3% for EFBSR), whereas EFBSR had the best sensitivity (78.7% vs 76.4% for RELAPS). EFBSR ranged from 35.25 to 1.83 and the cutoff value to differentiate CA from other hypertrophic cardiopathy was an EFBSR &gt;7.75. Conclusions Our study demonstrates that in patients with LV hypertrophy, a new deformation parameter, the ejection fraction basal strain ratio (EFBSR) can accurately differentiate CA from other causes of myocardial thickening and can be used in routine practice for screening. FUNDunding Acknowledgement Type of funding sources: None.

Zipoy-Voorhees Gravitational Object as a Source of High-Energy Relativistic Particles

The Zipoy-Voorhees solution is known as the γ-metric and/or q-metric being static and axisymmetric vacuum solution of Einstein field equations which becomes strong curvature naked singularity. The metric is characterized by two parameters, namely, the mass M and the dimensionless deformation parameter γ. It is shown that the velocity of test particle orbiting around the central γ-object can reach the speed of light, consequently, the total energy of the particle will be very high for a specific value the deformation parameter of the spacetime. It is also shown that causality problem arises in the interior region of the physical singularity for the specific value of the deformation parameter when test particles can move with superluminal velocity being greater than the speed of light that might be an additional tool for explaining the existence of tachyons for γ>1/2 which are invisible for an observer.

Analyzing the Effects of Topological Defect (TD) on the Energy Spectra and Thermal Properties of LiH, TiC and I2 Diatomic Molecules

In this study, the impacts of TD on the energy spectra and thermal properties of LiH, TiC and I2 diatomic molecules is considered. The Schrodinger equation in cosmic string spacetime is solved with the generalized Morse potential using the well-known (NU) method. The energy spectra and eigenfunction are obtained respectively. The energy spectra is used to obtain the partition function which is then used to evaluate the thermal properties of the system is evaluated accordingly. We find that the energy spectra in the presence of the TD differ from their flat Minkowski spacetime analogue. The effects of the deformation parameter and TD on the thermal properties of the system is also analysed in detail. We observe that the specific heat capacity of the system tends to exhibit quasi-saturation as the deformation parameter and topological defect approaches unity. The results of our study can be applied in the astrophysical situation where these modifications exist in the understanding of spectroscopical data and it may be used as a probe of the presence of a cosmic string or a global monopole in the Universe.

Superstatistics of Diatomic Molecules with the Shifted Deng-Fan Potential Model

In this article, we discuss the thermodynamic properties of the shifted Deng-Fan potential for HCl, CrH, CuLi, and ScF diatomic molecules using the q-deformed superstatistics approach. The partition function is obtained with the help of the generalized Boltzmann factor from the modified Dirac delta distribution. In addition, thermodynamic functions such as entropy, specific heat capacity, free energy, and mean energy are obtained using the partition function. Our results are presented graphically, and the ordinary statistical quantities are recovered when the deformation parameter tends to zero. Our results may be useful in the study of thermal fluctuations in atomic and molecular systems involving short-range interactions.