We study the renormalized energy-momentum tensor of cosmological scalar fluctuations during the slow-rollover regime for power-law inflation and find that it is characterized by a negative energy density at the leading order, with the same time behavior as the background energy. The average expansion rate appears decreased by the backreaction of the effective energy of cosmological fluctuations, but this value is comparable with the energy of the background only if inflation starts at a Planckian energy. We also find that, for this particular model, the first- and second-order inflaton fluctuations are decoupled and satisfy the same equation of motion. To conclude, the fourth-order adiabatic expansion for the inflaton scalar field is evaluated for a general potential $V(\varphi )$.

We study the interior spacetimes of stars in the Palatini formalism of $f(R)$ gravity and derive a generalized Tolman-Oppenheimer-Volkoff and mass equation for a static, spherically symmetric star. We show that matching the interior solution with the exterior Schwarzschild-de Sitter solution in general gives a relation between the gravitational mass and the density profile of a star, which is different from the one in general relativity. These modifications become negligible in models for which $\delta F(R)\equiv \partial f/\partial R-1$ is a decreasing function of $R$ however. As a result, both Solar System constraints and stellar dynamics are perfectly consistent with $f(R)=R-{\mu }^4/R$.

We study the possibility of complete family unification in higher-dimensional space-time. Three families of matters in $SU(5)$ grand unified theory are derived from a single bulk multiplet of the $SU(N)$ gauge group ($N\ge 9$) in the framework of $S^1/Z_2$ orbifold models. In the case of the direct orbifold breaking down to the standard model gauge group, there are models in which bulk fields from a single multiplet and a few brane fields compose three families of quarks and leptons.

We use a new set of Collins functions to update a previous prediction on the azimuthal asymmetries of pion production in a semi-inclusive deep-inelastic scattering process on a transversely polarized nucleon target. We find that the calculated results can give a good explanation to the HERMES experiment with the new parametrization, and this can enrich our knowledge of the fragmentation process. Furthermore, with two different approaches of distribution and fragmentation functions, we present a prediction on the azimuthal asymmetries of pion and kaon production at the kinematics region of the experiments E06010 and E06011 planned at Jefferson Lab. It is shown that the results are insensitive to the models for the pion case. However, the results for kaon production are sensitive to different approaches of distribution and fragmentation functions. This is helpful to clarify some points in the study of the azimuthal spin asymmetries and fragmentation functions in hadronization processes.

We compare results of the $k_t$-factorization approach and the next-to-leading order collinear-factorization approach for photon-jet correlations in $pp$ and $p\overline{p}$ collisions at Relativistic Heavy Ion Collider, Tevatron, and Large Hadron Collider energies. We discuss correlations in the azimuthal angle as well as in the two-dimensional space of transverse momentum of photon and jet. Different unintegrated parton distributions (UPDF) are included in the $k_t$-factorization approach. The results depend on UPDFs used. The standard collinear approach gives a cross section comparable to the $k_t$-factorization approach. For correlations of the photon and any jet the next-to-leading order (NLO) contributions dominate at relatively small azimuthal angles as well as for asymmetric transverse momenta. For correlations of the photon with the leading jet (the one having the biggest transverse momentum) the NLO approach gives zero contribution at ${\varphi }_{-}<\pi /2$, which opens a possibility to study higher-order terms and/or UPDFs in this region.

We study the effect of the $\sigma (600)$ and $a_1(1260)$ resonances in the ${\rho }^0\to {\pi }^{+}{\pi }^{-}\gamma$ decay within the meson dominance model. Major effects are driven by the mass and width parameters of the $\sigma (600)$, and the usually neglected contribution of the $a_1(1260)$, although small by itself, may become sizable through its interference with pion bremsstrahlung, and the proper relative sign can favor the central value of the experimental branching ratio. We present a procedure, using the gauge invariant structure of the resonant amplitudes, to kinematically enhance the resonant effects in the angular and energy distribution of the photon. We also elaborate on the coupling constants involved.

We introduce exposure as a means to making balanced comparisons of the sensitivities of long-baseline neutrino experiments to a nonzero ${\theta }_{13}$, to $CP$ violation, and to the neutrino mass hierarchy. We illustrate its use by comparing the sensitivities of possible upgrades of superbeam experiments, namely, $\mathrm{NO}\nu {\mathrm{A}}^{*}$, T2KK, and experiments with wide band beams. For the proposed exposures, we find the best nominal $CP$ violation performance for T2KK. For equal exposures, a wide band beam experiment has the best mass hierarchy performance. The physics concept on which $\mathrm{NO}\nu {\mathrm{A}}^{*}$ is based has the best potential for discovering $CP$ violation only for exposures above a threshold value.

We compute the dilatation generator in the $\mathfrak{s}\mathfrak{u}(2)$ sector of planar $\mathcal{N}=4$ super-Yang-Mills theory at four loops. We use the known world-sheet scattering matrix to constrain the structure of the generator. The remaining few coefficients can be computed directly from Feynman diagrams. This allows us to confirm previous conjectures for the leading contribution to the dressing phase which is proportional to $\zeta (3)$.

We present a new asymptotically flat time-machine model made solely of vacuum and dust. The spacetime evolves from a regular spacelike initial hypersurface S and subsequently develops closed timelike curves. The initial hypersurface S is asymptotically flat and topologically trivial. The chronology violation occurs in a compact manner; namely, the first closed causal curves form at the boundary of the future domain of dependence of a compact region in S (the core). This central core is empty, and so is the external asymptotically flat region. The intermediate region surrounding the core (the envelope) is made of dust with positive energy density. This model trivially satisfies the weak, dominant, and strong energy conditions. Furthermore, it is governed by a well-defined system of field equations which possesses a well-posed initial-value problem.

Extremal charged black holes are BPS solutions. It is commonly thought that their nonextremal counterparts are not. Further, experience with BPS solutions in flat spacetime suggests that all BPS solutions are supersymmetric; i.e. that they are invariant under some supersymmetry charges of either the original field theory or an appropriately extended version thereof. Using nonextremal Reissner-Nordström black holes as counterexamples, we show that neither of these expectations is universally valid. These black holes correspond to a one-parameter family of BPS solutions. By showing that, subject to one very plausible assumption, no generalized Killing spinor can be constructed for these, we show that there is no supergravity theory for which these BPS solutions preserve a fraction of the supersymmetry, nor is there an associated Witten-Nester positive energy bound.

In some models of supersymmetry breaking, modulus fields are heavy enough to decay before big bang nucleosynthesis. But the large entropy produced via moduli decay significantly dilutes the preexisting baryon asymmetry of the Universe. We study whether the Affleck-Dine mechanism can provide enough baryon asymmetry which survives the dilution, and find several situations in which a desirable amount of baryon number remains after the dilution. The possibility of nonthermal dark matter is also discussed. This provides the realistic cosmological scenario with heavy moduli.

The inhomogeneous ionization state of the Universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order $\sim 0.01\mu \mathrm{K}$, and local peak values of $\sim 0.1\mu \mathrm{K}$, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensing effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.

We present upper limits on the gravitational wave emission from 78 radio pulsars based on data from the third and fourth science runs of the LIGO and GEO 600 gravitational wave detectors. The data from both runs have been combined coherently to maximize sensitivity. For the first time, pulsars within binary (or multiple) systems have been included in the search by taking into account the signal modulation due to their orbits. Our upper limits are therefore the first measured for 56 of these pulsars. For the remaining 22, our results improve on previous upper limits by up to a factor of 10. For example, our tightest upper limit on the gravitational strain is $2.6\times {10}^{-25}$ for PSR $\mathrm{J}1603-7202$, and the equatorial ellipticity of PSR $\mathrm{J}2124–3358$ is less than ${10}^{-6}$. Furthermore, our strain upper limit for the Crab pulsar is only 2.2 times greater than the fiducial spin-down limit.

We study $CP$ violation in $e^{+}{e}^{-}\to {\tilde{\chi }}_i^{+}{\tilde{\chi }}_j^{-}$ in the framework of the minimal supersymmetric standard model. Though the cross section of this process is $CP$-even at the tree level even for polarized electron-positron beams, we show that it contains a $CP$-odd part at one-loop order and there are $CP$-odd observables that can in principle be measured even using unpolarized electron-positron beams. The relevant diagram calculations are briefly discussed, and the results of selected (box) diagram computations are shown.

Recent work suggests nontrivial relations between generalized parton distributions on the one hand and (naive time-reversal odd) transverse momentum dependent distributions on the other. Here we review the present knowledge on such type of relations. Moreover, as far as spectator model calculations are concerned, the existing results are considerably extended. While various relations between the two types of parton distributions can be found in the framework of spectator models, so far no nontrivial model-independent relations have been established.

We compare results of the $k_t$-factorization approach and the next-to-leading-order collinear-factorization approach for dijet correlations in proton-proton collisions at RHIC energies. We discuss correlations in azimuthal angle as well as correlations in two-dimensional space of transverse momenta of two jets. Some $k_t$-factorization subprocesses are included for the first time in the literature. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on unintegrated gluon distribution functions (UGDF)/unintegrated parton distribution function (UPDF) used. For the collinear next-to-leading order (NLO) case, the situation depends significantly on whether we consider correlations of any two jets or correlations of leading jets only. In the first case, the $2\to 2$ contributions associated with soft radiations summed up in the $k_t$-factorization approach dominate at $\varphi \sim \pi$ and at equal moduli of jet transverse momenta. The collinear NLO $2\to 3$ contributions dominate over $k_t$-factorization cross section at small relative azimuthal angles as well as for asymmetric transverse-momentum configurations. In the second case, the NLO contributions vanish at small relative azimuthal angles and/or large jet transverse-momentum disbalance due to simple kinematical constraints. There are no such limitations for the $k_t$-factorization approach. All this makes the two approaches rather complementary. The role of several cuts is discussed and quantified.

We discuss the recent proposal of implementing doubly special relativity in configuration space by means of Finsler geometry. Although this formalism leads to a consistent description of the dynamics of a particle, it does not seem to give a complete description of the physics. In particular, the Finsler line element is not invariant under the deformed Lorentz transformations of doubly special relativity. We study in detail some simple applications of the formalism.

A four-dimensional Lorentz-breaking non-Abelian Chern-Simons-like action is generated as a one-loop perturbative correction via an appropriate Lorentz-breaking coupling of the non-Abelian gauge field to a spinor field. This term is shown to be regularization dependent, but nevertheless it can be found unambiguously in different regularization schemes at zero and at finite temperature.

Based on the generalized uncertainty principle, we study the entropy of a four-dimensional black hole by counting degrees of freedom near the horizon and obtain the (finite) entropy proportional to the surface area at the horizon without a cutoff introduced in the conventional brick-wall method.

We study the gauge/gravity dual of a finite temperature field theory at finite isospin chemical potential by considering a probe of two coincident D7-branes embedded in the AdS-Schwarzschild black hole background. The isospin chemical potential is obtained by giving a vacuum expectation value to the time component of the non-Abelian gauge field on the brane. The fluctuations of the non-Abelian gauge field on the brane are dual to the $SU(2)$ flavor current in the field theory. For the embedding corresponding to vanishing quark mass, we calculate all Green functions corresponding to the components of the flavor current correlator. We discuss the physical properties of these Green functions, which go beyond linear response theory. In particular, we show that the isospin chemical potential leads to a frequency-dependent isospin diffusion coefficient.