We show that a degenerate neutrino mass spectrum can be realized in the neutrino mass anarchy hypothesis, if the neutrino Yukawa and right-handed neutrino mass matrices are given by the Wishart matrix, i.e., products of $N\times 3$ rectangular random matrices, whose eigenvalue distribution tends to degenerate for large $N$. The mixing angle and charge-parity (CP) phase distributions are determined by either the Haar measure of U(3) or that of SO(3). We study how large $N$ is allowed to be without tension with the observed neutrino mass squared differences and find that the predicted value of $m_{ee}$ can be within the reach of future $0\nu \beta \beta$ experiments especially for $N$ on the high side of the allowed range.

We compare the solutions to the short baseline neutrino anomaly based on oscillations to sterile neutrinos and the stochastic neutrino mixing mechanism (SNMM) through an analysis of the present neutrino data. The SNMM suggests worse fits than a $3+1$ sterile neutrino model, although it cannot be discarded by present data. We propose an experiment to distinguish between both solutions, based on placing a ${}^8\mathrm{Li}$ source inside a 5 kton-yr detector (like SNO). We studied the sensitivity of such an experiment, which makes it possible to discriminate within $2\sigma$ the SNMM from the $3+1$ sterile hypothesis for some particular values of the relevant parameters in 5 kton-yr of running.

We study all possible texture zeros in the Majorana neutrino mass matrix which are allowed from neutrino oscillation as well as cosmology data when the charged lepton mass matrix is assumed to take the diagonal form. In the case of one-zero texture, we write down the Majorana phases which are assumed to be equal and the lightest neutrino mass as a function of the Dirac $CP$ phase. In the case of two-zero texture, we numerically evaluate all the three $CP$ phases and lightest neutrino mass by solving four real constraint equations. We then constrain texture zero mass matrices from the requirement of producing correct baryon asymmetry through the mechanism of leptogenesis by assuming the Dirac neutrino mass matrix to be diagonal. Adopting a type I seesaw framework, we consider the $CP$-violating out of equilibrium decay of the lightest right-handed neutrino as the source of lepton asymmetry. Apart from discriminating between the texture zero mass matrices and light neutrino mass hierarchy, we also constrain the Dirac and Majorana $CP$ phases so that the observed baryon asymmetry can be produced. In two-zero texture, we further constrain the diagonal form of the Dirac neutrino mass matrix from the requirement of producing correct baryon asymmetry.

Using a data sample of 106 million $\psi (3686)$ events collected with the BESIII detector operated at the BEPCII storage ring, we study for the first time the decays ${\chi }_{cJ}\to \varphi K_S^0{K}^{\pm }{\pi }^{\mp }$ and ${\chi }_{cJ}\to \varphi K^{+}{K}^{-}{\pi }^0$ in the E1 radiative transition $\psi (3686)\to \gamma {\chi }_{cJ}$. The decays are dominated by the three-body decay ${\chi }_{cJ}\to \varphi K^{*}(892)\overline{K}$. We measure branching fractions for this reaction via the neutral and charged $K^{*}(892)$ and find them consistent with each other within the expectation of isospin symmetry. In the $K\overline{K}\pi$ invariant mass distribution, a structure near the $K^{*}(892)\overline{K}$ mass threshold is observed, and the corresponding mass and width are measured to be $1412\pm 4(\text{stat})\pm 8(\text{sys})\mathrm{MeV}/c^2$ and $\mathrm{\Gamma }=84\pm 12(\text{stat})\pm 40(\text{sys})\mathrm{MeV}$, respectively. The observed state favors an assignment to the $h_1(1380)$, considering its possible $J^{\mathrm{PC}}$ and comparing its mass, width and decay mode to those reported in the Particle Data Group.

We study electric field quench in $\mathcal{N}=2$ strongly coupled gauge theory, using the AdS/CFT correspondence. To do so, we consider the aforementioned system which is subjected to a time-dependent electric field indicating an out of equilibrium system. Defining the equilibration time $t_{\text{eq}}$, at which the system relaxes to its final equilibrium state after injecting the energy, we find that the rescaled equilibration time $k^{-1}{t}_{\text{eq}}$ decreases as the transition time $k$ increases. Therefore, we expect that for sufficiently large transition time, $k\to \infty$, the relaxation of the system to its final equilibrium can be an adiabatic process. On the other hand, we observe a universal behavior for the fast quenches, $k\ll 1$, meaning that the rescaled equilibration time does not depend on the final value of the time-dependent electric field. Our calculations generalized to systems in various dimensions also confirm the universalization process which seems to be a typical feature of all strongly coupled gauge theories that admit a gravitational dual.

Closed strings spinning in ${\mathrm{AdS}}_3\times S^3\times T^4$ with mixed Ramond-Ramond and Neveu-Schwarz-Neveu-Schwarz three-form fluxes are described by a deformation of the one-dimensional Neumann–Rosochatius integrable system. In this article we find general solutions to this system that can be expressed in terms of elliptic functions. We consider closed strings rotating either in $S^3$ with two different angular momenta or in ${\mathrm{AdS}}_3$ with one spin. To find the solutions, we will need to extend the Uhlenbeck integrals of motion of the Neumann–Rosochatius system to include the contribution from the flux. In the limit of pure Neveu-Schwarz-Neveu-Schwarz flux, where the problem can be described by a supersymmetric Wess-Zumino-Witten model, we find exact expressions for the classical energy in terms of the spin and the angular momenta of the spinning string.

We propose a QCD axion model that avoids the cosmological domain wall problem, introducing a global $SU(3{)}_{\mathrm{f}}$ family symmetry in which we embed the unwanted Peccei-Quinn (PQ) discrete symmetry. The spontaneous breaking of $SU(3{)}_{\mathrm{f}}$ and PQ symmetry predicts eight NG bosons as well as axion, all of which contribute to the energy density of the Universe as dark radiation. The deviation from the standard model prediction of dark radiation can be observed by future observations of cosmic microwave background fluctuations. Our model also predicts a sizable exotic kaon decay rate, which is marginally consistent with the present collider data and would be tested by future collider experiments.

The challenging issue of determining the correct $f(R)$ among several possibilities is revised here by means of numerical reconstructions of the modified Friedmann equations around the redshift interval $z\in [0,1]$. Frequently, a severe degeneracy between $f(R)$ approaches occurs, since different paradigms correctly explain present time dynamics. To set the initial conditions on the $f(R)$ functions, we involve the use of the so-called cosmography of the Universe, i.e., the technique of fixing constraints on the observable Universe by comparing expanded observables with current data. This powerful approach is essentially model independent, and correspondingly we got a model-independent reconstruction of $f(R(z))$ classes within the interval $z\in [0,1]$. To allow the Hubble rate to evolve around $z\le 1$, we considered three relevant frameworks of effective cosmological dynamics, i.e., the $\mathrm{\Lambda }\mathrm{CDM}$ model, the Chevallier–Polarski–Linder parametrization, and a polynomial approach to dark energy. Finally, cumbersome algebra permits passing from $f(z)$ to $f(R)$, and the general outcome of our work is the determination of a viable $f(R)$ function, which effectively describes the observed Universe dynamics.

Frame dragging (Lense-Thirring effect) is generally associated with rotating astrophysical objects. However, it can also be generated by electromagnetic fields if electric and magnetic fields are simultaneously present. In most models of astrophysical objects, macroscopic charge neutrality is assumed and the entire electromagnetic field is characterized in terms of a magnetic dipole component. Hence, the purely electromagnetic contribution to the frame dragging vanishes. However, strange stars may possess independent electric dipole and neutron stars independent electric quadrupole moments that may lead to the presence of purely electromagnetic contributions to the frame dragging. Moreover, recent observations have shown that in stars with strong electromagnetic fields, the magnetic quadrupole may have a significant contribution to the dynamics of stellar processes. As an attempt to characterize and quantify the effect of electromagnetic frame dragging in these kinds of astrophysical objects, an analytic solution to the Einstein-Maxwell equations is constructed here on the basis that the electromagnetic field is generated by the combination of arbitrary magnetic and electric dipoles plus arbitrary magnetic and electric quadrupole moments. The effect of each multipole contribution on the vorticity scalar and the Poynting vector is described in detail. Corrections on important quantities such the innermost stable circular orbit (ISCO) and the epicyclic frequencies are also considered.

The phenomenon discovered in 2009 by Bañados, Silk and West where particle collisions can achieve arbitrary high center-of-mass (c.m.) energies close to the event horizon of an extreme Kerr black hole, has generated a lot of interest. Although rotation seemed to be an essential requirement, it was later shown that arbitrary high energies can also be achieved for collisions between radially moving particles near the horizon of the electrically charged extreme Reissner-Nordström black hole. Recently Patil and Joshi claimed that instead of spinning up the black hole one can also crank up the c.m. energy of particle collisions by “charging up” a static black hole with a massless scalar field. In this regard they showed that infinite energies can be attained in the vicinity of the naked singularity of the Janis-Newman-Wincour (JNW) spacetime, which contains a massless scalar field that also becomes infinite at the position of the curvature singularity. In this study we show that Patil and Joshi’s claim does not apply for other static black hole systems endowed with a massless scalar field. In particular we consider the well-known Bekenstein black hole and the recently discovered Martínez-Troncoso-Zanelli black hole, and show that the expression of the c.m. energy for particle collisions near the event horizons of these black holes is no different than the corresponding case with vanishing scalar field represented by the Schwarzschild solution. Moreover by studying the motion of scalar test charges that interact with the background scalar field in these black hole spacetimes we show that the resulting c.m. energies are even smaller than in the case of free particles. This shows that the infinite energies obtained by Patil and Joshi may not be due to the fact that the black hole contains a massless scalar field, but may be instead related to the geometry of the naked singularity in the JNW spacetime. An analogous case of infinite c.m. energy in the vicinity of a naked singularity is also presented.

We investigate properties of higher-dimensional generally rotating black-hole spacetimes, so-called Kerr–NUT–(anti)–de Sitter spacetimes, as well as a family of related spaces which share the same explicit and hidden symmetries. In these spaces, we study a particle motion in the presence of a weak electromagnetic field and compare it with its operator analogies. First, we find general commutativity conditions for classical observables and for their operator counterparts, then we investigate a fulfillment of these conditions in the Kerr–NUT–(anti)–de Sitter and related spaces. We find the most general form of the weak electromagnetic field compatible with the complete integrability of the particle motion and the comutativity of the field operators. For such a field we solve the charged Hamilton-Jacobi and Klein-Gordon equations by separation of variables.

The character of the central density profile in the Lemaître-Tolman (LT) solutions plays a fundamental role in their application as cosmological models. This same character is studied here for these solutions used to model complete gravitational collapse. A necessary condition for the development of a black hole (not even locally naked singularities) is developed. This condition allows a finite (invariantly) defined range in central density cusps. If one demands no density cusps in the initial conditions, then this work shows that the LT solutions never produce even locally naked singularities.

We show that Solar System tests can place very strong constraints on K-mouflage models of gravity, which are coupled scalar field models with nontrivial kinetic terms that screen the fifth force in regions of large gravitational acceleration. In particular, the bounds on the anomalous perihelion of the Moon imposes stringent restrictions on the K-mouflage Lagrangian density, which can be met when the contributions of higher-order operators in the static regime are sufficiently small. The bound on the rate of change of the gravitational strength in the Solar System constrains the coupling strength $\beta$ to be smaller than 0.1. These two bounds impose tighter constraints than the results from the Cassini satellite and big bang nucleosynthesis. Despite the Solar System restrictions, we show that it is possible to construct viable models with interesting cosmological predictions. In particular, relative to $\mathrm{\Lambda }\mathrm{CDM}$, such models predict percent-level deviations for the clustering of matter and the number density of dark matter haloes. This makes these models predictive and testable by forthcoming observational missions.

Certain physical quantities that characterize neutron stars and quark stars (e.g. their mass, spin angular momentum, and quadrupole moment) have recently been found to be interrelated in a manner that is approximately insensitive to their internal structure. Such approximately universal relations are useful to break degeneracies in data analysis and model selection for future radio, x-ray, and gravitational wave observations. Although the pressure inside compact stars is most likely nearly isotropic, certain scenarios have been put forth that suggest otherwise, for example due to magnetic fields or phase transitions in their interior. We investigate here whether pressure anisotropy affects the approximate universal relations and, if so, whether it prevents their use in future astrophysical observations. We achieve this by numerically constructing slowly rotating and tidally deformed, anisotropic, compact stars in general relativity to third order in stellar rotation relative to the mass shedding limit. We adopt simple models for pressure anisotropy where the matter stress-energy tensor is diagonal for a spherically symmetric spacetime but the tangential pressure differs from the radial one. We find that the equation-of-state variation increases as one increases the amount of anisotropy, but within the anisotropy range studied in this paper (motivated from anisotropy due to crystallization of the core and pion condensation), anisotropy affects the universal relations only weakly. The relations become less universal by a factor of 1.5–3 relative to the isotropic case when anisotropy is maximal, but even then they remain approximately universal to 10%. We find evidence that this increase in variability is strongly correlated to an increase in the eccentricity variation of isodensity contours, which provides further support for the emergent approximate symmetry explanation of universality. Whether one can use universal relations in actual observations ultimately depends on the currently unknown amount of anisotropy inside stars, but within the range studied in this paper, anisotropy does not prevent the use of universal relations in gravitational wave astrophysics or in experimental relativity. We provide an explicit example of the latter by simulating a binary pulsar/gravitational wave test of dynamical Chern–Simons gravity with anisotropic neutron stars. The increase in variability of the universal relations due to pressure anisotropy could affect their use in future x-ray observations of hot spots on rotating compact stars. Given expected observational uncertainties, however, the relations remain sufficiently universal for use in such observations if the anisotropic modifications to the moment of inertia and the quadrupole moment are less than 10% of their isotropic values.

We study pion production from proton synchrotron radiation in the presence of strong magnetic fields by using the exact proton propagator in a strong magnetic field and explicitly including the anomalous magnetic moment. In this exact quantum field approach the magnitude of pion synchrotron emission turns out to be much smaller than that obtained in the semiclassical approach. However, we also find that the anomalous magnetic moment of the proton greatly enhances the production rate about by 2 orders of magnitude.

The space weather impacts propagation of galactic cosmic rays (CRs) in the heliosphere as explained by the diffusion-convection mechanism which predicts that the variation in CR intensity should be anticorrelated with changes in solar wind velocity (${\mathrm{V}}_{\mathrm{SW}}$). Several unrelated solar phenomena, including periodic ones such as 27 d solar rotation, annual, 11 yr solar activity, 22 yr solar magnetic cycle etc., and transient ones, for example, Forbush decreases (FDs), and ground level enhancements generally caused by solar flares or coronal mass ejections also affect CR intensity on Earth. These solar phenomena make a quantitative study of dependence of CR intensity on ${\mathrm{V}}_{\mathrm{SW}}$ rather difficult. Here, the high statistics muon data of six years (2000–2005) from the large GRAPES-3 muon telescope have been used to study the correlation between ${\mathrm{V}}_{\mathrm{SW}}$ and CR intensity. Data gathered during these six years were used after minimizing the contribution of various unrelated solar phenomena outlined above. We observed a strong anticorrelation between the variations in ${\mathrm{V}}_{\mathrm{SW}}$ and CR intensity at a significance of $19\sigma$.

Due to Earth’s revolution around the Sun, the expected scattering rate in direct dark matter searches is annually modulated. This modulation is expected to differ between experiments when given as a function of recoil energy $E_{\mathrm{R}}$, e.g. due to the gravitational focusing effect of the Sun. A better variable to compare results among experiments employing different targets is the minimum speed $v_{\min }$ a dark matter particle must have to impart a recoil energy $E_{\mathrm{R}}$ to a target nucleus. It is widely believed that the modulation expressed as a function of $v_{\min }$ is common to all experiments, irrespective of the dark matter distribution. We point out that the annual modulation as a function of $v_{\min }$, and in particular the times at which the rate is maximum and minimum, could be very different depending on the detector material. This would be an indication of a scattering cross section with nonfactorizable velocity and target material dependence. Observing an annual modulation with at least two different target elements would be necessary to identify this type of cross section.

We calculate the next-to-leading order (NLO) QCD corrections to $J/\psi$ associated with $W^{+}b$ production from top quark decay. Our results show that the decay width for process $t\to J/\psi +W^{+}+b+X$ at the leading order is significantly enhanced by the NLO QCD corrections. This process has the potential to be detected at the LHC. It provides an interesting signature that could be studied at the LHC, and if the $J/\psi$ associated production with $W^{+}b$ from top quark decay is really detected, it will be useful for testing the nonrelativistic QCD factorization formalism.

In this article, the prospects for studying the tensor structure of the $HZZ$ vertex with the LHC experiments are presented. The structure of tensor couplings in Higgs di-boson decays is investigated by measuring the asymmetries and by studying the shapes of the final state angular distributions. The expected background contributions, detector resolution, and trigger and selection efficiencies are taken into account. The potential of the LHC experiments to discover sizeable non-Standard Model contributions to the $HZZ$ vertex with 300 and $3000{\mathrm{fb}}^{-1}$ is demonstrated.