We study the properties of the relativistic, steady, axisymmetric, low angular momentum, inviscid, advective, geometrically thin accretion flow in a Kerr-Taub-NUT (KTN) spacetime which is characterized by the Kerr parameter ($a_{\mathrm{k}}$) and NUT parameter ($n$). Depending on $a_{\mathrm{k}}$ and $n$ values, KTN spacetime represents either a black or a naked singularity. We solve the governing equations that describe the relativistic accretion flow in KTN spacetime and obtain all possible global transonic accretion solutions around KTN black hole in terms of the energy $(\mathcal{E})$ and angular momentum ($\lambda$) of the flow. We identify the region of the parameter space in $\lambda -\mathcal{E}$ plane that admits the flow to possess multiple critical points for KTN black hole. We examine the modification of the parameter space due to $a_{\mathrm{k}}$ and $n$ and find that the role of $a_{\mathrm{k}}$ and $n$ in determining the parameter space is opposite to each other. This clearly indicates that the NUT parameter $n$ effectively mitigate the effect of black hole rotation in deciding the accretion flow structure. Further, we calculate the disc luminosity ($L$) corresponding to the accretion solutions around the KTN black hole and for a given set of $a_{\mathrm{k}}$ and $n$, we obtain the maximum luminosity $(L_{\max })$ by freely varying $\lambda$ and $\mathcal{E}$. We observe that $L_{\max }$ decreases with the increase of $n$ irrespective of $a_{\mathrm{k}}$. In addition, we also investigate all possible flow topologies around the naked singularity and find that there exists a region around the naked singularity which remains inaccessible to the flow. We study the critical point properties for naked singularities and find that the flow possesses maximum of four critical points. Finally, we obtain the parameter space for multiple critical points for naked singularity and find that parameter space is shrunk and shifted to lower $\lambda$ and higher $\mathcal{E}$ side as $a_{\mathrm{k}}$ is increased which ultimately disappears.

Data streams of gravitational-wave detectors are polluted by transient noise features, or “glitches,” of instrumental and environmental origin. In this work we investigate the use of total variation methods and learned dictionaries to mitigate the effect of those transients in the data. We focus on a specific type of transient, “blip" glitches, as this is the most common type of glitch present in the LIGO detectors and their waveforms are easy to identify. We randomly select 100 blip glitches scattered in the data from advanced LIGO’s O1 run, as provided by the citizen-science project Gravity Spy. Our results show that dictionary-learning methods are a valid approach to model and subtract most of the glitch contribution in all cases analyzed, particularly at frequencies below $\sim 1\mathrm{kHz}$. The high-frequency component of the glitch is best removed when a combination of dictionaries with different atom length is employed. As a further example we apply our approach to the glitch visible in the LIGO-Livingston data around the time of merger of binary neutron star signal GW170817, finding satisfactory results. This paper is the first step in our ongoing program to automatically classify and subtract all families of gravitational-wave glitches employing variational methods.

The Brans-Dicke theory of gravity is one of the oldest ideas to extend general relativity by introducing a nonminimal coupling between the scalar field and gravity. The Solar System tests put tight constraints on the theory. In order to evade these constraints, various screening mechanisms have been proposed. These screening mechanisms allow the scalar field to couple to matter as strongly as gravity in low density environments while suppressing it in the Solar System. The Vainshtein mechanism, which is found in various modified gravity models such as massive gravity, braneworld models and scalar tensor theories, suppresses the scalar field efficiently in the vicinity of a massive object. This makes it difficult to test these theories from gravitational wave observations. We point out that the recently found scalar gravitational wave memory effect, which is caused by a permanent change in spacetime geometry due to the collapse of a star to a back hole can be significantly enhanced in the Brans-Dicke theory of gravity with the Vainshtein mechanism. This provides a possibility to detect scalar gravitational waves by a network of three or more gravitational wave detectors.

We propose the $SU(3{)}_C\times SU(3{)}_L\times U(1{)}_X$ model arising from $SU(6)$ breaking. One family of the Standard Model (SM) fermions arises from two $\overline{6}$ representations and one 15 representation of $SU(6)$ gauge symmetry. To break the $SU(3{)}_C\times SU(3{)}_L\times U(1{)}_X$ gauge symmetry down to the SM, we introduce three $SU(3{)}_L$ triplet Higgs fields, where two of them come from the $\overline{6}$ representation while the other one from the 15 representation. We study the gauge boson masses and Higgs boson mass in detail, and find that the vacuum expectation value (VEV) of the Higgs field for $SU(3{)}_L\times U(1{)}_X$ gauge symmetry breaking is around 10 TeV. The neutrino masses and mixing can be generated via the littlest inverse seesaw mechanism. In particular, we have normal hierarchy for neutrino masses and the lightest active neutrino is massless. Also, we consider constraints from the charged lepton flavor changing decays as well. Furthermore, introducing two $SU(3{)}_L$ adjoint fermions, one $SU(3{)}_C$ adjoint scalar, and one $SU(3{)}_L$ triplet scalar, we can achieve gauge coupling unification within 1%. These extra particles can provide a dark matter candidate as well.

We propose to search for millicharged particles in electron colliders operated with the center-of-mass energies at $\mathcal{O}(1–10)\mathrm{GeV}$, which include Belle II, BESIII, BABAR, and also the proposed experiment Super Tau Charm Factory (STCF). We use the monophoton final state at electron colliders to probe the parameter space of millicharged particles, that is spanned by millicharge $\epsilon$ and mass $m$. We find that electron colliders have sensitivity to the previously unexplored parameter space for millicharged particles with MeV–GeV mass: $\epsilon \lesssim \mathcal{O}({10}^{-1})$ for $0.5\mathrm{GeV}\lesssim m\lesssim 3.5\mathrm{GeV}$ in BABAR, $\epsilon \lesssim \mathcal{O}({10}^{-3})$ for $0.1\mathrm{GeV}\lesssim m\lesssim 1.5\mathrm{GeV}$ in BESIII, $\epsilon \lesssim {10}^{-3}-{10}^{-2}$ for $0.1\mathrm{GeV}\lesssim m\lesssim 4\mathrm{GeV}$ in Belle II, and $\epsilon \lesssim \mathcal{O}({10}^{-4})$ for $1\mathrm{MeV}\lesssim m\lesssim 1\mathrm{GeV}$ in STCF.

We study the effective string description of spacelike Polyakov loop correlators at finite temperature with the goal of describing the behavior of the spacelike string tension in the vicinity of the deconfinement transition. To this end we construct the partition function of the Nambu-Goto effective string theory in presence of a compact transverse direction of length $L$ equal to the inverse temperature. We then show that, under particular conditions, our result can be interpreted as the partition function of the $T\overline{T}$ deformation of the 2d quantum field theory describing a compactified bosonic field and that this mapping allows a deeper insight on the behavior of the spacelike observables of the theory. In particular we show, by imposing that the spectrum of the model obeys the inviscid Burgers equation, that the $T\overline{T}$ deformations follow well-defined trajectories in the parameter space $(\sigma ,L)$ of the model, where $\sigma$ is the string tension, which are characterized by a constant value of the dimensionless compactification radius $\rho =L\sqrt{\sigma /2\pi }$. We discuss the potential usefulness of these results for studying the spacelike string tension of the underlying lattice gauge theory and its behavior across the deconfinement transition.

We study the photon self-energy in magnetized chiral plasma by solving the response of electromagnetic field perturbations in chiral kinetic theory with Landau level states. With lowest Landau level approximation and in the collisionless limit, we find solutions for three particular perturbations: the parallel electric, static perpendicular electric field, and static perpendicular magnetic field, corresponding to chiral magnetic wave, drift state, and tilted state, from which we extract components of photon self-energy in different kinematics. We that show no solution is possible for more general field perturbations. We argue that this is an artifact of the collisionless limit: while static solutions corresponding to the drift state and tilted state can be found, they cannot be realized dynamically without interaction between Landau levels. We also discuss the possible manifestation of side-jump effects due to both boost and rotation, with the latter due to the presence of background magnetic field.

We investigate the stability of the magnetic dual chiral density wave (MDCDW) phase of cold and dense QCD against collective low-energy fluctuations of the order parameter. The appearance of additional structures in the system free energy due to the explicit breaking of the rotational and isospin symmetries by the external magnetic field play a crucial role in the analysis. The new structures stiffen the spectrum of the thermal fluctuations in the transverse direction, thereby avoiding the Landau-Peierls instability that affects single-modulated phases at arbitrarily low temperatures. The lack of Landau-Peierls instabilities in the MDCDW phase makes this inhomogeneous phase of dense quark matter of particular interest for the physics of neutron stars.

In the present work, we analyze the $P$-wave singly heavy baryon spectrum belonging to ${\mathbf{6}}_F$ by combining the observations of the heavy baryon states, and restudy the strong decays of the $1P$-wave ${\mathrm{\Sigma }}_b$ states within the $j\text{−}j$ coupling scheme using the chiral quark model. We obtain that (i) the structure ${\mathrm{\Sigma }}_b(6097)$ observed in the ${\mathrm{\Lambda }}_b\pi$ final state may arise from the overlapping of ${\mathrm{\Sigma }}_b|J^P={\frac{3}{2}}^{-},2⟩$ and ${\mathrm{\Sigma }}_b|J^P={\frac{5}{2}}^{-},2⟩$. (ii) The broad structure ${\mathrm{\Sigma }}_b(6072)$ observed in the ${\mathrm{\Lambda }}_b\pi \pi$ final state may arise from the overlapping of ${\mathrm{\Sigma }}_b|J^P={\frac{1}{2}}^{-},1⟩$ and ${\mathrm{\Sigma }}_b|J^P={\frac{3}{2}}^{-},1⟩$. (iii) The missing state ${\mathrm{\Sigma }}_b|J^P={\frac{1}{2}}^{-},0⟩$ is most likely to be a narrow state with a width of $\mathrm{\Gamma }\sim 10\mathrm{MeV}$, and mainly decays into the ${\mathrm{\Lambda }}_b\pi$ channel.

We report searches for $B^0\to \text{invisible}$ and $B^0\to \text{invisible}+\gamma$ decays, where the energy of the photon is required to be larger than 0.5 GeV. These results are obtained from a $711{\mathrm{fb}}^{-1}$ data sample that contains $772\times {10}^{6}B\overline{B}$ pairs and was collected near the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We observe no significant signal for either decay and set upper limits on their branching fractions at 90% confidence level of $\mathcal{B}(B^0\to \text{invisible})<7.8\times {10}^{-5}$ and $\mathcal{B}(B^0\to \text{invisible}+\gamma )<1.6\times {10}^{-5}$.

The zigzag model is a relativistic $N$-body system arising in the high-energy limit of the worldsheet scattering in adjoint two-dimensional QCD. We prove classical Liouville integrability of this model by providing an explicit construction of $N$ charges in involution. Furthermore, we also prove that the system is maximally superintegrable by constructing $N-1$ additional independent charges. All of these charges are piecewise linear functions of coordinates and momenta. The classical time delays are determined algebraically from this integrable structure. The resulting $S$-matrix is the same as in the $N$-particle subsector of a massless $T\overline{T}$ deformed fermion.

We systematically investigate the possibilities of realizing the spontaneous $CP$ violation in Type IIB flux compactifications on toroidal orientifolds. Our detailed analysis for a generic choice of three-form fluxes leads to the presence of flat directions, where $CP$-breaking and -conserving vacua are degenerate, indicating that flux compactifications are not sufficient to realize the spontaneous $CP$ violation. Furthermore, the four-dimensional $CP$ can be embedded into the duality symmetries, namely modular symmetries for a particular choice of fluxes.

A nearly black, gravitationally intense star of a semitransparent, spherical, massive shell containing a few pointlike light sources inside would be perceived not like a three-dimensional ball for a localized observer outside the shell in terms of the affine or binocular distance. As the radius of the spherical shell approaches the Schwarzschild radius, the perceived distance between the front and rear surfaces of the shell would go to zero, while the images of most of the interior emitters would squeeze around the shell surfaces in terms of the affine or binocular distance. So, the Schwarzschild black hole formed from the star would be thought of as a two-dimensional membrane for the observers who can only measure the binocular distance and/or affine distance. However, the depth information of a point source inside the nearly black star can still be resolved in terms of the radar or luminosity distance, which needs the knowledge about the radar signals or standard candles sent in earlier by the observer outside the star. This suggests that at late times of gravitational collapse the area law of the entropy would dominate over the volume law for outside observers due to the loss of the knowledge about the ingoing probes earlier.

It has recently been argued that there may be a nontrivial four-dimensional limit of the higher-dimensional Gauss-Bonnet and Lovelock interactions and that this might provide a loophole allowing for new four-dimensional gravitational theories, possibly without a standard Lagrangian. We investigate this claim by studying tree-level graviton scattering amplitudes, allowing us to draw conclusions independently of the Lagrangian. By taking four-dimensional limits of higher-dimensional scattering amplitudes of the Gauss-Bonnet theory, we find four-dimensional amplitudes that are different from general relativity; however, these amplitudes are not new since they all come from certain scalar-tensor theories. The nontrivial limit that does not lead to infinite strong coupling around flat space leads to $(\partial \varphi {)}^4$ theory. We argue that there cannot be any six-derivative purely gravitational four-point amplitudes in any dimension other than those coming from Lovelock theory by directly constructing the on-shell amplitudes. In particular, there can be no new such amplitudes in four dimensions beyond those of general relativity. We also present some new results on the spin-averaged cross section for graviton-graviton scattering in general relativity and Gauss-Bonnet theory in arbitrary dimensions.

The speed of gravitational waves for a single observation can be measured by the time delay among gravitational-wave detectors with Bayesian inference. Then multiple measurements can be combined to produce a more accurate result. From the near simultaneous detection of gravitational waves and gamma rays originating from GW170817/GRB 170817A, the speed of gravitational wave signal was found to be the same as the speed of the gamma rays to approximately one part in ${10}^{15}$. Here we present a different method of measuring the speed of gravitational waves, not based on an associated electromagnetic signal but instead by the measured transit time across a geographically separated network of detectors. While this method is far less precise, it provides an independent measurement of the speed of gravitational waves. For GW170817, a binary neutron star inspiral observed by Advanced LIGO and Advanced Virgo, by fixing sky localization of the source at the electromagnetic counterpart the speed of gravitational waves is constrained to 90% confidence interval (0.97c, 1.02c), where c is the speed of light in a vacuum. By combing ten binary black hole (BBH) events and the binary neutron star event from the first and second observing runs of Advanced LIGO and Advanced Virgo, the 90% confidence interval is narrowed down to (0.97c, 1.01c). The accurate measurement of the speed of gravitational waves allows us to test the general theory of relativity. We further interpret these results within the test framework provided by the gravitational standard-model extension (SME). In doing so, we obtain simultaneous constraints on four of the nine nonbirefringent, nondispersive coefficients for Lorentz violation in the gravity sector of the SME and place limits on the anisotropy of the speed of gravity.

It is generally believed that the shadows of either a black hole or naked singularity arise due to photon spheres developing in these spacetimes. Here we propose a new spherically symmetric naked singularity spacetime which has no photon sphere, and we show that the singularity casts a shadow in the absence of the photon sphere. We discuss some novel features of this shadow and the lightlike geodesics in this spacetime. We compare the shadow of the naked singularity here with shadows cast by Schwarzschild black hole and the first type of Joshi-Malafarina-Narayan (JMN1) naked singularity, where for the last two spacetimes the shadow is formed due to the presence of a photon sphere. It is seen, in particular, that the size of shadow of the singularity is considerably smaller than that of a black hole. Our analysis shows that the shadow of this naked singularity is distinguishable from the shadow of a Schwarzschild black hole and the JMN1 naked singularity. These results are useful and important in the context of recent observations of shadow of the M87 Galactic center.

The orbital velocity profile of circular timelike geodesics in the equatorial plane of a Kerr black hole has a nonmonotonic radial behavior, provided that the spin parameter $a$ of the black hole is bigger than a certain critical value $a_c\approx 0.9953M$. Here the orbital velocity is measured with respect to the locally nonrotating frame, and the nonmonotonic behavior, which is known as the Aschenbach effect, occurs only for corotating orbits. Using the Mathisson-Papapetrou-Dixon equations for a massive spinning particle, we investigate the Aschenbach effect for test particles with spin. In addition to the black-hole spin, the absolute value of the particle’s spin and its orientation (parallel or antiparallel to the black-hole spin) also play an important role for the Aschenbach effect. We determine the critical value $a_c$ of the spin parameter of the Kerr black hole where the Aschenbach effect sets in as a function of the spin of the probe. We consider not only black holes ($a^2\le M^2$) but also naked singularities ($a^2>M^2$). Whereas for spinless (geodesic) particles the orbital velocity is always monotonically decreasing if the motion is counterrotating, we find that for spinning particles in counterrotating motion with antiparallel spin around a naked singularity the orbital velocity is increasing on a certain radius interval.

In this paper we study the light bending caused by a slowly rotating source in the context of quadratic theories of gravity, in which the Einstein-Hilbert action is extended by additional terms quadratic in the curvature tensors. The deflection angle is computed employing the method based on the Gauss-Bonnet theorem and working in the approximation of a weak lens; also, we assume that the source and observer are at an infinite distance. The formalism presented is very general and applies to any spacetime metric in the limit of weak gravitational field and slow rotation. We find the explicit formula for the deflection angle for several local and nonlocal theories, and also discuss some phenomenological implications.

We perform magnetospheric studies in the modified gravity (MOG) framework to investigate effects of MOG on radio pulsar energetics with the main question being “can MOG explain how radio pulsars turn into radio-quiet ones?” In order to realize our aim, first, we have obtained exact vacuum analytical solutions of Maxwell equations for magnetic fields in the exterior of neutron stars in MOG. Then we have derived the analytical expressions for Goldreich-Julian charge density and unscreened parallel electric field solving the Poisson equation in the MOG frame. Calculations have shown that effects of MOG shift the radio pulsar death line up in $P\dot{P}$ diagram rend-ring objects that are radio loud in general relativity radio quiet in MOG. Using observational data, we estimate the upper limit for parameter $\alpha$ for the millisecond pulsars J2145-0750, J0024-7204D, and J0024-7204H, as $\alpha =1.6011$, 3.06528, and 0.9747, respectively.

We use anisotropic fluid cosmology to describe the present, dark energy-dominated Universe without assuming the presence of dark matter. The resulting anisotropic fluid spacetime naturally generates inhomogeneities at small scales, triggered by an anisotropic stress, that could therefore be responsible for structure formation at these scales. We show that the dynamics of the scale factor $a$ is described by the usual Friedmann-Lemaître-Robertson-Walker cosmology and decouples completely from that describing inhomogeneities. Assuming that the fluid inherits the equation of state from galactic dynamics, we show that, in the large scale regime, it can be described as a generalized Chaplygin gas. We find that our model fits well the distance modulus experimental data of type Ia supernovae, thus correctly modeling the observed accelerated expansion of the Universe. Conversely, in the small scale regime, we use cosmological perturbation theory to derive the power spectrum $P(k)$ for mass density distribution. At short wavelengths, we find a $1/k^4$ behavior, in good accordance with the observed correlation function for matter distribution at small scales.