Search

We revisit and extend the study of null geodesics around a slowly rotating black hole in Chern-Simons modified gravity. We employ the Hamilton-Jacobi formalism to derive the equations for the shadow profile and determine its shape. We compare our results with numerical ray tracing, finding good agreement within the validity of our approximations for slow rotation and small Chern-Simons coupling. We constrain the model parameters using data from the observed shadow of SgrA$^*$., Comment: 17 pages, 7 figures

We analyze cosmography as a tool to constrain modified gravity theories. We take four distinct models and obtain their parameters in terms of the cosmographic parameters favored by observational data of strong gravitational lensing. We contrast with the values obtained by direct comparison between each model and the observational data. In general, we find consistency between the two approaches at 2$\sigma$ for all models considered in this work. Our study bridges the gap between theoretical predictions of modified gravity and empirical observations of strong gravitational lensing, providing a simple methodology to test the validity of these models., Comment: 18 pages, 8 figures

Rastall gravity is a modified gravity proposal that incorporates a non-conserved energy momentum tensor (EMT). We study the equivalence between Rastall gravity and general relativity, analyzing its consequences for an EMT of dark matter and dark energy. We find that the translation between the Rastall and Einstein interpretations modifies the equation of state for each component. For instance, cold dark matter can translate into warm dark matter. If the EMT components are allowed to interact, the translation also changes the type of interaction between the components., Comment: 18 pages, 4 figures

We find that it is possible to increase sensitivity to low energy physics in a third or fourth DUNE-like module with careful controls over radiopurity and targeted modifications to a detector similar to the DUNE Far Detector design. In particular, sensitivity to supernova and solar neutrinos can be enhanced with improved MeV-scale reach. A neutrinoless double beta decay search with $^{136}$Xe loading appears feasible. Furthermore, sensitivity to Weakly-Interacting Massive Particle (WIMP) Dark Matter (DM) becomes competitive with the planned world program in such a detector, offering a unique seasonal variation detection that is characteristic for the nature of WIMPs., Comment: arXiv admin note: substantial text overlap with arXiv:2203.08821

The {\it{Cosmological Boundary Flux Parameter}} is a novel proposal that attempts to explain the origin of the cosmological parameter $\Lambda$ purely by geometric nature. Then we implement this new approach to a flat FLRW universe along with a barotropic fluid. We present an ansatz in which $\Lambda$ is straightforwardly coupled to the matter sector; therefore, only one additional parameter was introduced: $\lambda$. Also, through a statistical analysis, using late-time data of observational Hubble and type Ia Supernovae, we computed the joint best-fit value of the free parameters by means of the affine-invariant MCMC. We want to emphasise that the joint analysis produces a smaller $H_{0}^{\rm CBFP}=69.80\rm\,\, Km \,s^{-1}\,Mpc^{-1}$ in contrast to the flat $\Lambda$CDM result $H_{0}^{\Lambda\rm CDM}=70.53\rm\,\, Km \,s^{-1}\,Mpc^{-1}$. The work presented here seeks to contribute to the discussion of the possible explanation for the cosmos' acceleration, together with tackling other important questions in modern cosmology., Comment: 15 pages, 6 figures

We find that it is possible to increase sensitivity to low energy physics in a third or fourth DUNE-like module with careful controls over radiopurity and some modifications to a detector similar to the DUNE Far Detector design. In particular, sensitivity to supernova and solar neutrinos can be enhanced with improved MeV-scale reach. A neutrinoless double beta decay search with $^{136}$Xe loading appears feasible. Furthermore, sensitivity to Weakly-Interacting Massive Particle (WIMP) Dark Matter (DM) becomes competitive with the planned world program in such a detector, offering a unique seasonal variation detection that is characteristic for the nature of WIMPs., Comment: contribution to Snowmass 2021

The propagation of gravitational waves offers new possibilities for testing the theory of gravity. Amongst these possibilities there is the luminosity distance of gravitational waves, $d_{gw}$. It has been proposed to study this property by means of phenomenological parametrizations, which in this work we confront to the actual predictions of Einstein-scalar-Gauss-Bonnet gravity, finding that the simplest parametrization performs better. We propose a novel parametrization that covers a wider range of models, in particular, within degenerate higher order scalar-tensor theories of gravity. Also, regarding model selection from best-fit parameters, we find that even quantities derived from $d_{gw}$ can lead to inconsistent model selection if they are treated independently. This highlights that it is essential to perform simultaneous analysis and include other types of data. We expect our findings to be relevant for future constraints on modified gravity based on the properties of standard sirens., Comment: 19 pages, 3 figures

In this paper we give a physical explanation to the accelerated expansion of the Universe, alleviating the tension between the discrepancy of Hubble constant measurements. By the Euler Cauchy stress principle, we identify a controversy on the lack of consideration of the surface forces contemplated in the study of the expansion of the Universe. We distinguish a new effect that modifies the spacetime fabric by means of the energy conservation equation. The resulting dynamical equations from the proposed hypothesis are contrasted to several testable astrophysical predictions. This paper also explains why we have not found any particle or fluid responsible for dark energy and clarifies the Cosmological Coincidence Problem. These explanations are achieved without assuming the existence of exotic matter of unphysical meaning or having to modify the Einstein's Field Equations., Comment: 15 pages, 5 figures, IJMPD Accepted

The deflection of light in the strong field limit is an important test for alternative theories of gravity. However, solutions for the metric that allow for analytic computations are not always available. We implement a hybrid analytic-numerical approximation to determine the deflection angle in static, spherically symmetrics pacetimes. We apply this to a set of numerical black hole solutions within the class of theories known as Degenerate Higher Order Scalar-tensor Theories. Comparing our results to a more time consuming full numerical integration, we find that we can accurately describe the deflection angle for light rays passing at arbitrary distances from the photon sphere with a combination of two analytic-numerical approximations. Furthermore, we find a range of parameters where our DHOST black holes predict strong lensing effects whose size is comparable with the uncertainty in the properties of the supermassive black hole in M87 reported by the Event Horizon Telescope, showing that strong lensing is a viable alternative to put constraints on these models., Comment: 22 pages, 8 figures

Graphene oxide (GO) is widely used in different applications, however once release into the environment it can change its structure and affect the transport of important contaminants such as arsenic. In this work we show that UV radiation, even in the range of 28-74 uW/cm2 of irradiance up to 120 h of exposure, can induce important changes in the structure of graphene oxide, by eliminating -OH and C=O functional groups. This reduction affected the stability of graphene oxide in water by decreasing its zeta potential from 41 to 37 mV with the increase of the exposure time. Our results showed that after 24 h of UV exposure, As(III) adsorption capacity decreased from 5 mg/g to 4.7 mg/g, however after 48 h of irradiation the adsorption increased with time, reaching 5.1 mg/g at 120 h under 74 uW/cm2 of irradiation. Computer modelling showed that even a degraded GO structure can have an interaction energy of 53 kcal/mol with H3AsO3. Furthermore, we observed that despite clear changes in surface composition and particle size, the reduction of graphene oxide maintained a high degree of cytotoxicity since cell viability decreased to 60% with a 50 ug/ml dose; except for the sample irradiated at 74 uW/cm2 for five days, which showed 20% with the same concentration.

An important consequence which comes from noncommutativity (NC) is undoubtedly the energy density characterized by a microscopic free parameter; indeed a Trans-Planckian parameter. However, its functional form is an interesting and useful equation which can be analyzed in astrophysical scenarios giving now astrophysical constraints. In this sense, this paper is devoted to explore the astrophysical consequences of an energy density with the same functional form of NC; mainly in stellar dynamics and rotation curves of galaxies. We start exploring toy models of stars with incompressible and polytropic fluids respectively, with the addition and coexistence with this new fluid. In both cases, we propose an appropriate constriction based on the difference between a correct and an anomalous behavior. As a complement, we explore the rotation curves of galaxies assuming that the halo is a fluid with the same characteristic of a NC equation, obtaining the range of values for the free parameter through the analysis of eighteen LSB galaxies. Our results are compared with traditional models studied in literature like Pseudoisothermal (PISO), Navarro-Frenk-White (NFW), Burkert and WaveDM dark matter models. Finally, we have computed the surface density, $\rho_i r_i$ for each dark matter model, where $i$ is for PISO, NFW, Burkert, WaveDM and NC macroscopic version. In the later case, following the results found using SPARC galaxy catalog, we have found a theoretical value of $116.97 M_\odot$ pc$^{-2}$ while the data analysis gives us a value of $144.21 M_\odot$ pc$^{-2}$., Comment: 17 pages, 7 figures, change title, Important improvements

Understanding the dynamics of fluid-driven sediment transport remains challenging, as it is an intermediate region between a granular material and a fluid flow. Boyer \textit{et al.}\citep{Boyer2011} proposed a local rheology unifying dense dry-granular and viscous-suspension flows, but it has been validated only for neutrally-buoyant particles in a confined system. Here we generalize the Boyer \textit{et al.}\citep{Boyer2011} model to account for the weight of a particle by addition of a pressure $P_0$, and test the ability of this model to describe sediment transport in an idealized laboratory river. We subject a bed of settling plastic particles to a laminar-shear flow from above, and use Refractive-Index-Matching to track particles' motion and determine local rheology --- from the fluid-granular interface to deep in the granular bed. Data from all experiments collapse onto a single curve of friction $\mu$ as a function of the viscous number $I_v$ over the range $10^{-5} \leq I_v \leq 1$, validating the local rheology model. For $I_v < 10^{-5}$, however, data do not collapse. Instead of undergoing a jamming transition with $\mu \rightarrow \mu_s$ as expected, particles transition to a creeping regime where we observe a continuous decay of the friction coefficient $\mu \leq \mu_s$ as $I_v$ decreases. The rheology of this creep regime cannot be described by the local model, and more work is needed to determine whether a non-local rheology model can be modified to account for our findings.

This paper is dedicated to revisit the modifications caused by branes in the collapse of a stellar structure under the Snyder-Oppenheimer scheme. Due to the homogeneity and isotropy of the model, we choose study the case of a closed geometry described by $k=1$, through the tool of dynamical systems. We revisit the different components of the star and its evolution during the stellar collapse, paying particular attention to the non-local effects and the quadratic terms of the energy momentum tensor that come from branes corrections. In the same vein we realize a phase portrait together with a stability analysis with the aim of obtain information about the attractors or saddle points of the dynamical system under different initial conditions in the density parameters, remarking the parameters that come from branes contributions., Comment: 7 pages, 5 figures

Density Functional Theory (DFT) calculations show a weak interaction between hydrogen and helium in iron, in contrast to previous reports of a strong trapping of hydrogen at helium. The strong preference of He and H to occupy regions with low electronic density (such as vacancies) explains this discrepancy, with vacancy-He and vacancy-H binding forces concealing the repulsive interaction between He and H. Furthermore, Rate Theory simulations based on our DFT-calculated V$_n$He$_m$H$_p$ cluster energetics predict, as it is observed in some experiments, that synergetic effects could be expected between H and He in iron under irradiation.

Structural studies of biological macromolecules are severely limited by radiation damage. Traditional crystallography curbs the effects of damage by spreading damage over many copies of the molecule of interest. X-ray lasers, such as the recently built LINAC Coherent Light Source (LCLS), offer an additional opportunity for limiting damage by out-running damage processes with ultrashort and very intense X-ray pulses. Such pulses may allow the imaging of single molecules, clusters or nanoparticles, but coherent flash imaging will also open up new avenues for structural studies on nano- and micro-crystalline substances. This paper addresses the theoretical potentials and limitations of nanocrystallography with extremely intense coherent X-ray pulses. We use urea nanocrystals as a model for generic biological substances and simulate primary and secondary ionization dynamics in the crystalline sample. Our results establish conditions for ultrafast nanocrystallography diffraction experiments as a function of fluence and pulse duration., Comment: 6 pages, 4 color figures

Using the ADM formalism in the minisuperspace, we obtain the commutative and noncommutative exact classical solutions and exact wave function to the Wheeler-DeWitt equation with an arbitrary factor ordering, for the anisotropic Bianchi type I cosmological model, coupled to a scalar field, cosmological term and barotropic perfect fluid. We introduce noncommutative scale factors, considering that all minisuperspace variables $\rm q^i$ do not commute, so the symplectic structure was modified. In the classical regime, it is shown that the anisotropic parameter $\rm \beta_{\pm nc}$ and the field $\phi$, for some value in the $\lambda_{eff}$ cosmological term and noncommutative $\theta$ parameter, present a dynamical isotropization up to a critical cosmic time $t_{c}$; after this time, the effects of isotropization in the noncommutative minisuperspace seems to disappear. In the quantum regimen, the probability density presents a new structure that corresponds to the value of the noncommutativity parameter., Comment: 17 pages, 6 figures, Acepted in IJTP

Data mining is a recognized predictive tool in a variety of areas ranging from bioinformatics and drug design to crystal structure prediction. In the present study, an electronic structure implementation has been combined with structural data from the Inorganic Crystal Structure Database to generate results for highly accelerated electronic structure calculations of about 22,000 inorganic compounds. It is shown how data mining algorithms employed on the database can identify new functional materials with desired materials properties, resulting in a prediction of 136 novel materials with potential for use as detector materials for ionizing radiation. The methodology behind the automatized ab-initio approach is presented, results are tabulated and a version of the complete database is made available at the internet web site http://gurka.fysik.uu.se/ESP/ (Ref.1)., Comment: Project homepage: http://gurka.fysik.uu.se/ESP/

Radiation damage is an unavoidable process when performing structural investigations of biological macromolecules with X-ray sources. In crystallography this process can be limited through damage distribution in a crystal, while for single molecular imaging it can be outrun by employing short intense pulses. Secondary electron generation is crucial during damage formation and we present a study in urea, as model for biomaterial. From first principles we calculate the band structure and energy loss function, and subsequently the inelastic electron cross section in urea. Using Molecular Dynamics simulations, we quantify the damage and study the magnitude and spatial extent of the electron cloud coming from an incident electron, as well as the dependence with initial energy., Comment: 6 pages, 5 figures. Several major modifications. Revised version as accepted in EPL. Corrected figures 4 and 5, corresponding to published erratum

In this paper we present the noncommutative Bianchi Class A cosmological models coupled to barotropic perfect fluid. The commutative and noncommutative quantum solution to the Wheeler-DeWitt equation for any factor ordering, to the anisotropic Bianchi type II cosmological model are found, using a stiff fluid ($\gamma=1$). In our toy model, we introduce noncommutative scale factors, is say, we consider that all minisuperspace variables $\rm q^i$ does not commute, so the simplectic structure was modified., Comment: 8 pages, revtex4

We present the classical solutions to the Einstein field equations derived using the WKB-like and Hamilton procedures. The investigation is carried out in the commutative and noncommutative scenario for the Bianchi type I cosmological model coupled to barotropic perfect fluid and $\lambda $ Cosmological for two different gauges. Noncommutativity is achieved by modifying the symplectic structure considering that all minisuperspace variables $\rm q^i$ does not commute and by a deformation between all the minisuperspace variables. In the gauge N=1, it is possible to obtain that the anisotropic parameter $\rm \beta_{\pm nc}$ tend to a constant curvature for large period of time considering different values in the noncommutative parameters $\theta$ and cosmological term. However, this behavior give the idea that is necessary introduce other class of matter in the models, for to have a real isotropization in the model, such as dark energy or dark matter., Comment: 15 pages, 1 figure

Using the canonical quantum theory of spherically symmetric pure gravitational systems, we present a direct correspondence between the Friedmann-Robertson-Walker (FRW) cosmological model in the interior of a Schwarzschild black hole and the nth energy eigenstate of a linear harmonic oscillator. Such type of universe has a quantized mass of the order of the Planck mass and harmonic oscillator wave functions, Comment: 7 pages, send to PRD

For high energy cosmic neutrinos Athar, Jezabek, and Yasuda (AJY) have recently shown that the existing data on neutrino oscillations suggests that cosmic neutrino flux at the AGN/GRB source, F(nu_e):F(nu_mu):F(nu_tau) approx 1:2:0, oscillates to F(nu_e):F(nu_mu):F(nu_tau) approx 1:1:1. These results can be confirmed at AMANDA, Baikal, ANTARES and NESTOR, and other neutrino detectors with a good flavor resolution. Here, we re-derive the AJY result from quasi bi-maximal mixing, and show that observation of F(nu_e):F(nu_\mu):F(nu_tau) approx 1:1:1 does not necessarily establish cosmic neutrino flux at the AGN/GRB source to be F(nu_e):F(nu_mu):F(nu_tau) approx 1:2:0., Comment: 8 pages [This preprint is no longer being pursued for publication. Its essential contents are now published as part of D. V. Ahluwalia, Ambiguity in source flux of cosmic/astrophysical neutrinos: Effects of bi-maximal mixing and quantum-gravity induced decoherence, Mod. Phys. Lett. A 16 (2001) 917-926]

The beta-delayed alpha spectrum from the decay of 8B has been measured with a setup that minimized systematic uncertainties that affected previous measurements. Consequently the deduced neutrino spectrum presents much smaller uncertainties than the previous recommendation. The 8B neutrino spectrum is found to be harder than previously recommended with about (10-20)% more neutrinos at energies between 12-14 MeV. The efficiencies of the 37Cl, 71Ga, 40Ar, and SuperKamiokande detectors are respectively, 3.6%, 1.4%, 5.7% and 1.8% larger than previously thought., Comment: 4 pages, 5 figures