We investigate how a Type IV future singularity can be included in the cosmological evolution of a well-known exponential model of inflation. In order to achieve this we use a two scalar field model, in the context of which the incorporation of the Type IV singularity can be consistently done. In the context of the exponential model we study, when a Type IV singularity is included in the evolution, an instability occurs in the slow-roll parameters, and in particular in the second slow-roll parameter. Particularly, if we abandon the slow-roll condition for both the scalars we shall use, then the most consistent description of the dynamics of the inflationary era is provided by the Hubble slow-roll parameters ${\epsilon }_H$ and ${\eta }_H$. Then, the second Hubble slow-roll parameter ${\eta }_H$, which measures the duration of the inflationary era, becomes singular at the point where the Type IV singularity is chosen to occur, while the Hubble slow-roll parameter ${\epsilon }_H$ is regular there. Therefore, this infinite singularity indicates that the occurrence of the finite-time singularity is responsible for the instability in the scalar field model we study. This sort of instability has its imprint on the dynamical system that can be constructed from the cosmological equations, with the dynamical system being unstable. Also the late-time evolution of the two scalar field system is studied, and in the context of the theoretical framework we use, late-time and early-time acceleration are described in a unified way. In addition, the instability due to the singularity mechanism we propose, is discussed in the context of other inflationary scalar potentials. Finally, we discuss the implications of such a singularity in the Hubble slow-roll parameters and we also critically discuss qualitatively, what implications could this effect have on the graceful exit problem of the exponential model.

With the possibility of testing massive gravity in the context of black hole physics in mind, we consider the radiation produced by a particle plunging from slightly below the innermost stable circular orbit into a Schwarzschild black hole. In order to circumvent the difficulties associated with black hole perturbation theory in massive gravity, we use a toy model in which we replace the graviton field with a massive scalar field and consider a linear coupling between the particle and this field. We compute the waveform generated by the plunging particle and study its spectral content. This permits us to highlight and interpret some important effects occurring in the plunge regime which are not present for massless fields, such as (i) the decreasing and vanishing, as the mass parameter increases, of the signal amplitude generated when the particle moves on quasicircular orbits near the innermost stable circular orbit; and (ii) in addition to the excitation of the quasinormal modes, the excitation of the quasibound states of the black hole.

Precision measurements of rare particle physics phenomena (flavor oscillations and decays, electric dipole moments, etc.) are often sensitive to the effects of new physics encoded in higher-dimensional operators with Wilson coefficients given by $\mathrm{C}/({\mathrm{\Lambda }}_{\mathrm{NP}}{)}^n$, where C is dimensionless, $n\ge 1$, and ${\mathrm{\Lambda }}_{\mathrm{NP}}$ is an energy scale. Many extensions of the Standard Model predict that ${\mathrm{\Lambda }}_{\mathrm{NP}}$ should be at the electroweak scale or above, and the search for new short-distance physics is often stated as the primary goal of experiments at the precision frontier. In rather general terms, we investigate the alternative possibility—$\mathrm{C}\ll 1$, and ${\mathrm{\Lambda }}_{\mathrm{NP}}\ll m_W$—to identify classes of precision measurements sensitive to light new physics (hidden sectors) that do not require an ultraviolet completion with additional states at or above the electroweak scale. We find that hadronic electric dipole moments, lepton number and flavor violation, nonuniversality, as well as lepton $g-2$ can be induced at interesting levels by hidden sectors with light degrees of freedom. In contrast, many hadronic flavor- and baryon number-violating observables, and precision probes of charged currents, typically require new physics with ${\mathrm{\Lambda }}_{\mathrm{NP}}\gtrsim m_W$. Among the leptonic observables, we find that a nonzero electron electric dipole moment near the current level of sensitivity would point to the existence of new physics at or above the electroweak scale.

We present the one-loop matching condition for the unpolarized and polarized generalized quark distributions in the nonsinglet case. The matching condition links the quasi distributions defined in terms of spacelike correlators at finite nucleon momentum to the light-cone distributions, and it is useful for extracting the latter from the former in a lattice QCD calculation. Our results show that at one-loop and leading power accuracy the matching for the light-cone generalized quark distribution $H$ ($\tilde{H}$) is nontrivial, whereas no matching is required for $E$ ($\tilde{E}$). Therefore, $E$ ($\tilde{E}$) can be smoothly approached by its quasi counterpart in the large momentum limit. We also present the matching for the distribution amplitude of the pion.

Hadron masses under strong magnetic fields are studied. In the presence of strong magnetic fields exceeding the QCD energy scale $eB\gg {\mathrm{\Lambda }}_{\mathrm{QCD}}^2$, $\mathrm{SU}(3{)}_{\text{flavor}}\otimes \mathrm{SU}(2{)}_{\text{spin}}$ symmetry of hadrons is explicitly broken so that the quark components of hadrons differ from those with zero or weak magnetic fields $eB\lesssim {\mathrm{\Lambda }}_{\mathrm{QCD}}^2$. Also, squeezing of hadrons by strong magnetic fields affects the hadron mass spectrum. We develop a quark model which appropriately incorporates these features and analytically calculate various hadron masses including mesons, baryons, and those with strangeness.

We investigate the properties of dibaryons containing $u$ and $d$ quarks in the constituent quark model. In constructing the ground state wave function, we choose the spatial part to be fully symmetric and the remaining color, isospin, and spin part to be antisymmetric so as to satisfy the Pauli principle. By adapting the isospin $\otimes$ spin ($IS$) coupling scheme that combines the isospin basis function with the spin basis function, and subsequently coupling this to the color singlet basis function, we construct the color $\otimes$ isospin $\otimes$ spin states compatible with the physical states of the dibaryon. By using the variational method, we then calculate the mass of the dibaryon in a nonrelativistic potential model, involving Coulomb, color confinement, and color-spin hyperfine interaction. In particular, to assess the stability for different types of the confinement potential, we introduce one that is linearly proportional to the interquark distance and another to its square root. For all cases considered, we find that there are no compact bound states against the strong decay.

In a scenario with two almost mass degenerate heavy sterile Majorana neutrinos with a mass $\sim 1\mathrm{GeV}$, we present the semileptonic decay widths of heavy charged pseudoscalars such as $B$ mesons, either lepton number violating ($B^{\pm }\to {\mu }^{\pm }{e}^{\pm }{\pi }^{\mp }$), or lepton number conserving ($B^{\pm }\to {\mu }^{\pm }{e}^{\mp }{\pi }^{\pm }$), mediated by such on-shell neutrinos. It had been explained in the literature that such decays may be eventually detected, and that they can present even detectable $CP$ violation effects. In this work we point out that, in addition, such decays may present detectable effects of heavy neutrino oscillation, allowing us to extract the oscillation length and thus the heavy neutrino mass difference $\mathrm{\Delta }{M}_N$, as well as a $CP$-violating Majorana phase.

Based on a sample of $1.31\times 10^9$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ events, 33,908 $\eta \to {\pi }^0{\pi }^0{\pi }^0$ events, and 1,888 ${\eta }^{\prime }\to {\pi }^0{\pi }^0{\pi }^0$ events are performed. The measured matrix elements of $\eta \to {\pi }^{+}{\pi }^{-}{\pi }^0$ are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of $\eta \to {\pi }^0{\pi }^0{\pi }^0$ and ${\eta }^{\prime }\to {\pi }^0{\pi }^0{\pi }^0$ are determined to be $-0.055\pm 0.014\pm 0.004$ and $-0.640\pm 0.046\pm 0.047$, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of 3. Final state interactions are found to have an important role in those decays.

We study a holographic gauge theory living in the ${\mathrm{AdS}}_4$ space-time at finite temperature. The gravity dual is obtained as a solution of the type IIB superstring theory with two free parameters, which correspond to four-dimensional cosmological constant ($\lambda$) and the dark radiation ($C$) respectively. The theory studied here is in the confining and chiral symmetry broken phase for $\lambda <0$ and small $C$. When $C$ is increased, the transition to the deconfinement phase has been observed at a finite value of $C/|\lambda |$. It is shown here that the chiral symmetry is still broken for a finite range of $C/|\lambda |$ in the deconfinement phase. In other words, the chiral phase transition occurs at a larger value of $C/|\lambda |$ than that of the deconfinement transition. So there is a parameter range of a new deconfinement phase with broken chiral symmetry. In order to study the properties of this phase, we performed a holographic analysis for the meson mass spectrum and other quantities in terms of the probe D7 brane. The results are compared with a linear sigma model. Furthermore, the entanglement entropy is examined to search for a sign of the chiral phase transition. Several comments are given for these analyses.

It is known that the sphere-level S-matrix element of four type II superstrings has one kinematic factor. At the low energy limit, this factor produces the kinematic factor of the corresponding Feynman amplitudes in the supergravity. It also produces higher-derivative couplings of four strings. In this paper, we explicitly calculate the kinematic factor of four Ramond-Ramond (RR) states in the supergravity. Using this factor, we then find the eight-derivative P-even and P-odd couplings of four RR fields, including the self-dual RR five-form field strength. We show that the P-even couplings are mapped to the standard ${\overline{R}}^4$ couplings by linear T-duality and S-duality transformations. We also confirm the P-even couplings with direct calculations in type II superstring theories.

A magnetic bag is an Abelian approximation to a large number of coincident $SU(2)$ Bogomol’nyi-Prasad-Sommerfield monopoles. In this paper we consider magnetic bags in hyperbolic space and derive their Nahm transform from the large-charge limit of the discrete Nahm equation for hyperbolic monopoles. An advantage of studying magnetic bags in hyperbolic space, rather than Euclidean space, is that a range of exact charge $N$ hyperbolic monopoles can be constructed, for arbitrarily large values of $N$, and compared with the magnetic bag approximation. We show that a particular magnetic bag (the magnetic disc) provides a good description of the axially symmetric $N$-monopole. However, an Abelian magnetic bag is not a good approximation to a roughly spherical $N$-monopole that has more than $N$ zeros of the Higgs field. We introduce an extension of the magnetic bag that does provide a good approximation to such monopoles and involves a spherical non-Abelian interior for the bag, in addition to the conventional Abelian exterior.

We extend the covariant variational approach for $SU(N)$ Yang-Mills theory in Landau gauge to nonzero temperatures. The renormalization of the zero-temperature case is revisited and it is shown that the same counterterms are sufficient to render the low-order Green’s function finite at nonzero temperature. We compute the ghost and gluon propagator numerically and show that it agrees in all qualitative respects with the results of high-precision lattice calculations.

We present a Lorentz-breaking supersymmetric algebra characterized by a critical exponent $z$. Such construction requires a nontrivial modification of the supercharges and superderivatives. The improvement of renormalizability for supersymmetric scalar QED is shown, and the Kählerian effective potentials are calculated in different cases. We also show how the theory flows naturally to the Lorentz symmetric case at low energies.

We analyze some dimension-five $CPT$-even and Lorentz-violating nonminimal couplings between fermionic and gauge fields in the context of the Dirac equation. After evaluating the nonrelativistic Hamiltonian, we discuss the behavior of the terms under discrete symmetries and analyze the implied effects. We then use the anomalous magnetic dipole moment and electron electric dipole moment measurements to reach upper bounds of 1 part in ${10}^{20}$ and ${10}^{24}(\mathrm{eV}{)}^{-1}$, improving the level of restriction on such couplings by at least 8 orders of magnitude. These upper bounds are also transferred to the Sun-centered frame by considering the Earth’s rotational motion.

Besides their astrophysical interest, compact stars also provide an arena for understanding the properties of theories of gravity that differ from Einstein’s general relativity. Numerous studies have shown that different modified theories of gravity can modify the bulk properties (such as mass and radius) of neutron stars for given assumptions on the microphysics. What is not usually stressed though is the strong degeneracy in the predictions of these theories for the stellar mass and radius. Motivated by this observation, in this paper we take an alternative route and construct a stellar structure formalism which, without adhering to any particular theory of gravity, describes in a simple parametrized form the departure from compact stars in general relativity. This “post-Tolman-Oppenheimer-Volkoff (TOV)” formalism for spherical static stars is inspired by the well-known parametrized post-Newtonian theory, extended to second post-Newtonian order by adding suitable correction terms to the fully relativistic TOV equations. We show how neutron star properties are modified within our formalism, paying special attention to the effect of each correction term. We also show that the formalism is equivalent to general relativity with an “effective” (gravity-modified) equation of state.

In this paper, we investigate the coexistence curves and molecule number densities of $f(R)$ anti-de Sitter (AdS) black holes and Gauss–Bonnet AdS black holes. Specifically, we work with the reduced parameter space and derive the analytic expressions of the universal coexistence curves that are independent of theory parameters. Moreover, we obtain the explicit expressions of the physical quantity describing the difference of the number densities of black hole molecules between the small and large black holes. It is found that both the coexistence curve and the difference of the molecule number densities of $f(R)$ AdS black holes coincide with those of Reissner–Nordström–AdS black holes. It may be attributed to the same equation of state they share in the reduced parameter space. The difference of the molecule number densities between the small and large Gauss–Bonnet AdS black holes exhibit different behavior. This may be attributed to the fact that the charge of the Reissner–Nordström-AdS black hole is nontrivial. Our research will not only deepen the understanding of both the physics along the coexistence curve and the underlying microscopic freedom of AdS black holes but also highlight the importance of the law of the corresponding states.

In a previous article we derived a class of solutions to the force-free magnetosphere in a Kerr background. Here, the streaming surface, defined by constant values of the toriodal component of the electromagnetic vector potential $A$, was generated by constant values of $\theta$. The electromagnetic current vector flowed along the infalling principle null geodesic vector of the geometry. Subsequently, we generalized this to obtain an outgoing principle null geodesic vector as well. In this article, we derive solutions that are complimentary to the above-mentioned criteria. Namely, here the solution has a streaming surface generated by spheres of constant radial coordinate $r$, and the current vector is generated by linear combinations of $m$ and $m^{\star }$, the remaining bases vectors in the Newman-Penrose null tetrad.

We investigate the stability of $D$ dimensional singly rotating Myers-Perry-AdS black holes under superradiance against scalar field perturbations. It is well known that small four dimensional rotating or charged Anti-de Sitter (AdS) black holes are unstable against superradiance instability of a scalar field. Recent works extended the existence of this instability to five dimensional rotating charged AdS black holes or static charged AdS black holes in arbitrary dimensions. In this paper we analytically prove that rotating small AdS black holes in arbitrary dimensions also shows superradiance instability irrespective of the value of the (positive) angular momentum quantum number. To do this we solve the Klein-Gordon equation in the slow rotation, low frequency limit. By using the asymptotic matching technique, we are able to calculate the real and imaginary parts of the correction terms to the frequency of the scalar field due to the presence of the black hole, confirming the presence of superradiance instability. We see that, unlike in the case of static AdS black holes, the analytical method is valid for rotating AdS black holes for any value of angular momentum number and spacetime dimensions. For comparison we derive the corresponding correction terms for Myers-Perry black holes in the black hole bomb formalism in the Appendix and see that the results are in agreement.

In this paper, we review the classification of the orbits followed by charged massive test particles in the gravitational background of the black hole solutions of Einstein-Born-Infeld spacetime. Even though some features are quite similar to those of Reissner-Nordström spacetime, there are also important differences, particularly those related to the effective potential governing the orbital motion. Explicit solutions involving Weierstrass functions are given for a pair of specific scenarios.

Many studies have been carried out since Padmanabhan proposed that the cosmic acceleration can be understood from the perspective that spacetime dynamics is an emergent phenomenon. Motivated by such a new paradigm, we first study the de Sitter universe from emergence of space. Next, we investigate general universes and then narrow down our discussion to one universe, with a detailed discussion of the possibility of describing our real universe classically. Furthermore, a constraint on $Ht$ and an estimated value of ${\tilde{\mathrm{\Omega }}}_{\mathrm{\Lambda }}$ (caused by ${\rho }_{\mathrm{vac}}$) can be derived from our model; a comparison with experiments is also presented. The results show the validity of our model.