Results for the naive-time-reversal-odd quark distributions in a light-cone quark model are presented. The final-state interaction effects are generated via single-gluon exchange mechanism. The formalism of light-cone wave functions is used to derive general expressions in terms of overlap of wave-function amplitudes describing the different orbital angular momentum components of the nucleon. In particular, the model predictions show a dominant contribution from $S$- and $P$-wave interference in the Sivers function and a significant contribution also from the interference of $P$ and $D$ waves in the Boer-Mulders function. The favorable comparison with existing phenomenological parametrizations motivates further applications to describe azimuthal asymmetries in hadronic reactions.

A variational principle is suggested within Riemannian geometry, in which an auxiliary metric and the Levi Civita connection are varied independently. The auxiliary metric plays the role of a Lagrange multiplier and introduces nonminimal coupling of matter to the curvature scalar. The field equations are 2nd order PDEs and easier to handle than those following from the so-called Palatini method. Moreover, in contrast to the latter method, no gradients of the matter variables appear. In cosmological modeling, the physics resulting from the alternative variational principle will differ from the modeling using the standard Palatini method.

We show that the phenomenon of spontaneous scalarization predicted in neutron stars within the framework of scalar-tensor tensor theories of gravity, also takes place in boson stars without including a self-interaction term for the boson field (other than the mass term), contrary to what was claimed before. The analysis is performed in the physical (Jordan) frame and is based on a $3+1$ decomposition of spacetime assuming spherical symmetry.

We investigate the strong gravitational lensing in a Kaluza-Klein black hole with squashed horizons. We find the size of the extra dimension imprints in the radius of the photon sphere, the deflection angle, the angular position, and magnification of the relativistic images. Supposing that the gravitational field of the supermassive central object of the Galaxy can be described by this metric, we estimated the numerical values of the coefficients and observables for gravitational lensing in the strong field limit.

A method of motion reconstruction of an isotropic compact source in the vicinity of a Schwarzschild black hole is described. The method is based on the analysis of the redshift and the luminous intensity of several images of the source and is most effective for the source located at the distance of several Schwarzschild radii to the black hole. The cases of three and two observed images are considered. The uniqueness of motion reconstruction is investigated for each case. The results are illustrated by an example of direct and inverse problem solution. An observational scenario that allows to obtain the information necessary for motion reconstruction is suggested.

We evaluate the neutrino-nucleon charged-current cross section at next-to-leading order in quantum chromodynamic corrections in the variable flavor number scheme and the fixed flavor number scheme, taking into account quark masses. The number scheme dependence is largest at the highest energies considered here, ${10}^{12}\mathrm{GeV}$, where the cross sections differ by approximately 13%. We illustrate the numerical implications of the inconsistent application of the fixed flavor number scheme.

I present a perturbative calculation of the spectrum of the Faddeev-Popov operator in Coulomb gauge in three dimensions, and Landau gauge in two and three dimensions, with an ansatz for the gluon propagator as the nonperturbative input. The results show how the low-lying Faddeev-Popov eigenvalue spectrum is modified as the first Gribov horizon is approached, and how the spectra can differ in Coulomb and Landau gauges.

We investigate the relation between the known decompositions of the nucleon spin into its constituents, thereby clarifying in what respect they are common and in what respect they are different essentially. The decomposition recently proposed by Chen et al. can be thought of as a nontrivial generalization of the gauge-variant Jaffe-Manohar decomposition so as to meet the gauge-invariance requirement of each term of the decomposition. We however point out that there is another gauge-invariant decomposition of the nucleon spin, which is closer to the Ji decomposition, while allowing the decomposition of the gluon total angular momentum into the spin and orbital parts. After clarifying the reason why the gauge-invariant decomposition of the nucleon spin is not unique, we discuss which decomposition is more preferable from an experimental viewpoint.

We study the flavor structure of four-dimensional (4D) effective theories, which are derived from extra dimensional theories with magnetic fluxes and non-Abelian Wilson lines. We study zero-mode wave functions in generic case and compute Yukawa couplings as well as four-point couplings. In our models, we also discuss non-Abelian discrete flavor symmetries such as $D_4$, $\Delta (27)$, and $\Delta (54)$. The orbifold background is also studied.

Puff field theory (PFT) is a low energy decoupling regime of string theory that still retains the nonlocal attributes of the parent theory—while preserving isotropy for its nonlocal degrees of freedom. It realizes an extended holographic dictionary at strong coupling and dynamical nonlocal states akin to defects or the surface operators of local gauge theories. In this work, we probe the nonlocal features of PFT using D3 branes. We find supersymmetric configurations that end on defects endowed with non-Abelian degrees of freedom. These are $2+1$ dimensional defects in the $3+1$ dimensional PFT that may be viewed as volume operators. We determine their $R$ charge, vacuum expectation value, energy, and gauge group structure.

We construct a Lifshitz-like version of five-dimensional (5D) QED which is UV completed and reduces at low energies to ordinary 5D QED. The UV quantum behavior of this theory is very smooth. In particular, the gauge coupling constant is finite at all energy scales and at all orders in perturbation theory. We study the IR properties of this theory, when compactified on a circle, and compare the one-loop energy dependence of the coupling in the Lifshitz theory with that coming from the standard 5D QED effective field theory. The range of validity of the 5D effective field theory is found to agree with the more conservative version of naive dimensional analysis.

We consider quantum electrodynamics in noncommutative spacetime by deriving a Seiberg-Witten map, nonperturbative in $\theta$, with fermions in the fundamental representation of the gauge group as an expansion in the coupling constant. Accordingly, we demonstrate the persistence of UV/IR mixing in noncommutative QED with charged fermions via a Seiberg-Witten map, extending the results of Schupp and You [P. Schupp and J. You, J. High Energy Phys. 08 (2008) 107.].

It is shown that loop divergences emerging in the Green functions in quantum field theory originate from correspondence of the Green functions to unmeasurable (and hence unphysical) quantities. This is because no physical quantity can be measured in a point, but in a region, the size of which is constrained by the resolution of measuring equipment. The incorporation of the resolution into the definition of quantum fields $\varphi (x)\to {\varphi }^{(A)}(x)$ and appropriate change of Feynman rules results in finite values of the Green functions. The Euclidean ${\varphi }^4$-field theory is taken as an example.

A thorough analysis of Galilean symmetries for the gravitational well problem on a noncommutative plane is presented. A complete closure of the one-parameter centrally extended Galilean algebra is realized for the model. This implies that the field theoretic model constructed to describe noncommutative gravitational quantum well in [A. Saha, Eur. Phys. J. C 51, 199 (2007).] is indeed independent of the coordinate choice. Hence the energy spectrum predicted by the model can be associated with the experimental results to establish the upper bound on a time-space noncommutative parameter. Interestingly, noncommutativity is shown to increase the gravitational pull on the neutron trapped in the gravitational well.

In general relativity coupled to Maxwell’s electromagnetism and charged matter, when the gravitational potential $W^2$ and the electric potential field $\varphi$ obey a relation of the form $W^2=a(-ϵ\varphi +b{)}^2+c$, where $a$, $b$, and $c$ are arbitrary constants, and $ϵ=\pm 1$ (the speed of light $c$ and Newton’s constant $G$ are put to one), a class of very interesting electrically charged systems with pressure arises. We call the relation above between $W$ and $\varphi$, the Weyl-Guilfoyle relation, and it generalizes the usual Weyl relation, for which $a=1$. For both, Weyl and Weyl-Guilfoyle relations, the electrically charged fluid, if present, may have nonzero pressure. Fluids obeying the Weyl-Guilfoyle relation are called Weyl-Guilfoyle fluids. These fluids, under the assumption of spherical symmetry, exhibit solutions which can be matched to the electrovacuum Reissner-Nordström spacetime to yield global asymptotically flat cold charged stars. We show that a particular spherically symmetric class of stars found by Guilfoyle has a well-behaved limit which corresponds to an extremal Reissner-Nordström quasiblack hole with pressure, i.e., in which the fluid inside the quasihorizon has electric charge and pressure, and the geometry outside the quasihorizon is given by the extremal Reissner-Nordström metric. The main physical properties of such charged stars and quasiblack holes with pressure are analyzed. An important development provided by these stars and quasiblack holes is that without pressure the solutions, Majumdar-Papapetrou solutions, are unstable to kinetic perturbations. Solutions with pressure may avoid this instability. If stable, these cold quasiblack holes with pressure, i.e., these compact relativistic charged spheres, are really frozen stars.

In this paper we construct an effective field theory (EFT) that describes long wavelength gravitational radiation from compact systems. To leading order, this EFT consists of the multipole expansion, which we describe in terms of a diffeomorphism invariant point particle Lagrangian. The EFT also systematically captures “post-Minkowskian” corrections to the multipole expansion due to nonlinear terms in general relativity. Specifically, we compute long distance corrections from the coupling of the (mass) monopole moment to the quadrupole moment, including up to two mass insertions. Along the way, we encounter both logarithmic short distance (UV) and long wavelength (IR) divergences. We show that the UV divergences can be (1) absorbed into a renormalization of the multipole moments and (2) resummed via the renormalization group. The IR singularities are shown to cancel from properly defined physical observables. As a concrete example of the formalism, we use this EFT to reproduce a number of post-Newtonian corrections to the gravitational wave energy flux from nonrelativistic binaries, including long distance effects up to 3 post-Newtonian ($v^6$) order. Our results verify that the factorization of scales proposed in the NRGR framework of Goldberger and Rothstein is consistent up to order 3PN.

We study the full spectrum of spherically symmetric solutions in the five-dimensional nonprojectable Horava-Lifshitz type gravity theories. For appropriate ranges of the coupling parameters, we have found several classes of solutions which are characterized by an ${\mathrm{AdS}}_5$, ${\mathrm{dS}}_5$, or flat large distance asymptotic behavior, plus the standard $1/r^2$ tail of the usual five-dimensional Schwarzschild black holes. In addition we have found solutions with an unconventional short or large distance behavior, and, for a special range of the coupling parameters, solutions which coincide with black hole solutions of conventional relativistic five-dimensional Gauss-Bonnet gravity.

We present an analysis of the absorption of acoustic waves by a black hole analogue in ($2+1$) dimensions generated by a fluid flow in a draining bathtub. We show that the low-frequency absorption length is equal to the acoustic hole circumference and that the high-frequency absorption length is 4 times the ergoregion radius. For intermediate values of the wave frequency, we compute the absorption length numerically and show that our results are in excellent agreement with the low- and high-frequency limits. We analyze the occurrence of superradiance, manifested as negative partial absorption lengths for corotating modes at low frequencies.

The collisions of cosmic string loops and the dynamics of junction formations in expanding backgrounds are studied. The key parameter controlling the dynamics of junction formation, the cosmic strings zipping and unzipping, is the relative size of the loops compared to the Hubble radius at the time of collision. We study analytically and numerically these processes for large superhorizon size loops, for small subhorizon size loops as well as for loops with the radii comparable to the Hubble radius at the time of collision.

Inflation is studied in the context of induced gravity (IG) $\gamma {\sigma }^{2}R$, where $R$ is the Ricci scalar, $\sigma$ a scalar field and $\gamma$ a dimensionless constant, and diverse symmetry-breaking potentials $V(\sigma )$ are considered. In particular we compared the predictions for Landau-Ginzburg and Coleman-Weinberg type potentials and their possible generalizations with the most recent data. We find that large field inflation generally leads to fewer constraints on the parameters and the shape of the potential whereas small field inflation is more problematic and, if viable, implies more constraints, in particular, on the parameter $\gamma$. We also examined the reheating phase and obtained an accurate analytical solution for the dynamics of the inflaton and the Hubble parameter by using a multiple scale analysis. The solutions were then used to study the average expansion of the Universe, the average equation of state for the scalar field and both the perturbative and resonant decays of the inflaton field.