It is shown that a nonminimal coupling between the scalar curvature and the matter Lagrangian density may account for the accelerated expansion of the Universe and provide, through mimicking, for a viable unification of dark energy and dark matter. An analytical exploration is first performed, and a numerical study is then used to validate the obtained results. The encountered scenario allows for a better grasp of the proposed mechanism, and sets up the discussion for improvements that can lead to a complete agreement with the observational data.

Motivated by Verlinde’s theory of entropic gravity, we give a tentative explanation to the Coulomb’s law with an entropic force. When trying to do this, we find the equipartition rule should be extended to charges and the concept of temperature should be reinterpreted. If one accepts the holographic principle as well as our generalizations and reinterpretations, then Coulomb’s law, the Poisson equation, and the Maxwell equations can be derived smoothly. Our attempt can be regarded as a new way to unify the electromagnetic force with gravity, from the entropic origin. Possibly some of our postulates are related to the $D$-brane picture of black hole thermodynamics.

Cosmic microwave background satellite missions as the ongoing Planck experiment are expected to provide the strongest constraints on a wide set of cosmological parameters. Those constraints, however, could be weakened when the assumption of a cosmological constant as the dark energy component is removed. Here we show that it will indeed be the case when there exists a coupling among the dark energy and the dark matter fluids. In particular, the expected errors on key parameters as the cold dark matter density and the angular diameter distance at decoupling are significantly larger when a dark coupling is introduced. We show that it will be the case also for future satellite missions as EPIC, unless CMB lensing extraction is performed.

We suggest that a weak isotriplet composite scalar possessing an unbroken $U(1)$ global symmetry naturally arises in technicolor models leading to an interesting type of dark matter candidate: the iTIMP. We propose explicit models of the iTIMP, study earth based constraints, and suggest possible collider signals.

The duality between QCD perturbative series and power corrections recently conjectured by Narison and Zakharov is analyzed. We propose to study correlations between both contributions as a diagnostics tool. A very strong correlation between perturbative and nonperturbative contributions is observed for several observables at zero and at finite temperature supporting the validity of the dual description.

We have derived the unitarity bounds in the high energy limit for the minimal $B-L$ extension of the standard model by analyzing the full class of Higgs and would-be Goldstone boson two-to-two scatterings at tree level. Moreover, we have investigated how these limits could vary at some lower critical value of the energy.

Most analyses of dark matter within supersymmetry assume the entire cold dark matter arising only from weakly interacting neutralinos. We study a new class of models consisting of $U(1{)}^n$ hidden sector extensions of the minimal supersymmetric standard model that includes several stable particles, both fermionic and bosonic, which can be interpreted as constituents of dark matter. In one such class of models, dark matter is made up of both a Majorana dark matter particle, i.e., a neutralino, and a Dirac fermion with the current relic density of dark matter as given by WMAP being composed of the relic density of the two species. These models can explain the PAMELA positron data and are consistent with the antiproton flux data, as well as the photon data from FERMI-LAT. Further, it is shown that such models can also simultaneously produce spin-independent cross sections which can be probed in CDMS-II, XENON-100, and other ongoing dark matter experiments. The implications of the models at the LHC and at the next linear collider (NLC) are also briefly discussed.

We study quark propagators near the confinement/deconfinement phase transition temperature in quenched-lattice simulation of QCD. We find that there is no qualitative change for the quark propagators in both phases. In the confinement phase, those effective quark masses in units of the critical temperature behave as a constant as a function of the temperature, while above the critical temperature, the value of the effective quark mass drops to circa half value.

We investigate the prompt photon production in deep inelastic scattering at HERA in the framework of the $k_T$-factorization QCD approach. Our study is based on the off-shell partonic amplitude $e{q}^{*}\to e\gamma q$, where the photon radiation from the leptons as well as from the quarks is taken into account. The unintegrated quark densities in a proton are determined using the Kimber-Martin-Ryskin prescription. We investigate both inclusive and jet-associated prompt photon production rates. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS Collaborations. We demonstrate that in the $k_T$-factorization approach the contribution from the quark radiation subprocess (QQ mechanism) is enhanced as compared to the leading-order collinear approximation.

$B^{\pm }\to {\pi }^{+}{\pi }^{-}{K}^{\pm }$ and ${\overline{B}}^0\to {\pi }^{+}{\pi }^{-}{\overline{K}}^0$ decay channels are analyzed within the QCD factorization scheme where final state interactions before and after hadronization are included. The $K^{*}(892)$ and $K_0^{*}(1430)$ resonance effects are taken into account using the presently known $\pi K$ strange vector and scalar form factors. The weak decay amplitudes, which are calculated at leading power in ${\Lambda }_{\mathrm{QCD}}/m_b$ and at the next-to-leading order in the strong coupling constant, include the hard-scattering and annihilation contributions. The end-point divergences of these weak final state interactions are controlled by two complex parameters determined through a fit to the available effective mass and helicity angle distribution, $CP$ asymmetry, and $K^{*}(892)$ branching ratio data. The predicted $K_0^{*}(1430)$ branching ratios and the calculated direct $CP$ violation asymmetries are compared to the Belle and BABAR Collaboration data.

We investigate neutron-antineutron oscillations in the Randall-Sundrum warped extra dimensional scenario. The four dimensional effective strengths of the relevant operators that induce the oscillations are calculated up to an arbitrary coupling along with their corresponding enhancements due to QCD 1-loop running effects. We find that the $\Delta B=2$ operators can be geometrically suppressed without fine tuning to within current experimental limits with a warped down four dimensional mass scale which can be as low as a fraction of a TeV.

In this paper we give all the details of the calculation that we presented in our previous paper [58], where the infrared structure of the maximally helicity violating gluon amplitudes in the planar limit for $\mathcal{N}=4$ super Yang-Mills theory was considered in the next-to-leading order of perturbation theory. Explicit cancellation of the infrared divergencies in properly defined inclusive cross sections is demonstrated first in a toy model example of “conformal QED” and then in the real $\mathcal{N}=4$ supersymmetric Yang-Mills theory. We give the full-length details both for the calculation of the real emission and for the diagrams with splitting in initial and final states. The finite parts for some inclusive differential cross sections are presented in an analytical form. In general, contrary to the virtual corrections, they do not reveal any simple structure. An example of the finite part containing just the log functions is presented. The dependence of inclusive cross section on the external scale related to the definition of asymptotic states is discussed.

Chiral symmetry of the 2-dimensional chiral Gross-Neveu model is broken explicitly by a bare mass term as well as a splitting of scalar and pseudoscalar coupling constants. The vacuum and light hadrons—mesons and baryons which become massless in the chiral limit—are explored analytically in leading order of the derivative expansion by means of a double sine-Gordon equation. Depending on the parameters, this model features new phenomena as compared to previously investigated 4-fermion models: spontaneous breaking of parity, a nontrivial chiral vacuum angle, twisted kinklike baryons whose baryon number reflects the vacuum angle, crystals with alternating baryons, and appearance of a false vacuum.

We propose Lagrangian and Hamiltonian formulations of a $N=4$ supersymmetric three-dimensional isospin-carrying particle moving in the non-Abelian field of a Wu-Yang monopole and in some specific scalar potential. This additional potential is completely fixed by $N=4$ supersymmetry, and in the simplest case of flat metrics it coincides with that which provides the existence of the Runge-Lenz vector for the bosonic subsector. The isospin degrees of freedom are described on the Lagrangian level by bosonic auxiliary variables forming $N=4$ supermultiplet with additional, also auxiliary, fermions. Being quite general, the constructed systems include such interesting cases as $N=4$ superconformally invariant systems with Wu-Yang monopole, the particles living in the flat ${\mathbb{R}}^3$ and in the $\mathbb{R}\times {\mathbb{S}}^2$ spaces and interacting with the monopole, and also the particles moving on three-dimensional sphere and pseudosphere with the Wu-Yang monopole sitting in the center. The superfield Lagrangian description of these systems is so simple that one could wonder to see how all couplings and the proper coefficients arise while passing to the component action.

We prove that a class of solutions to Einstein’s equations—originally discovered by McVittie in 1933—includes regular black holes embedded in Friedmann-Robertson-Walker cosmologies. If the cosmology is dominated at late times by a positive cosmological constant, the metric is regular everywhere on and outside the black hole horizon and away from the big-bang singularity, and the solutions asymptote in the future and near the horizon to the Schwarzschild-de Sitter geometry. For solutions without a positive cosmological constant the would-be horizon is a weak null singularity.

In general relativity, a gravitational wave has two polarization modes (tensor mode), but it could have additional polarizations (scalar and vector modes) in the early stage of the Universe, where the general relativity may not strictly hold and/or the effect of higher-dimensional gravity may become significant. In this paper, we discuss how to detect extra-polarization modes of stochastic gravitational wave background (GWB), and study the separability of each polarization using future space-based detectors such as BBO and DECIGO. We specifically consider two plausible setups of the spacecraft constellations consisting of two and four clusters, and estimate the sensitivity to each polarization mode of GWBs. We find that a separate detection of each polarization mode is rather sensitive to the geometric configuration and distance between clusters and that the clusters should be, in general, separated by an appropriate distance. This seriously degrades the signal sensitivity; however, for suitable conditions, the space-based detector can separately detect scalar, vector and tensor modes of GWBs with energy density as low as $h_0^2{\Omega }_{\mathrm{gw}}\sim {10}^{-15}$.

With the new physical interpretation of quasinormal modes proposed by Maggiore, the quantum area spectra of black holes have been investigated recently. Adopting the modified Hod’s treatment, results show that the area spectra for black holes are equally spaced and the spacings are in a unified form, $△A=8\pi \hslash$, in Einstein gravity. On the other hand, following Kunstatter’s method, the studies show that the area spectrum for a nonrotating black hole with no charge is equidistant. And for a rotating (or charged) black hole, it is also equidistant and independent of the angular momentum $J$ (or charge $q$) when the black hole is far from the extremal case. In this paper, we mainly deal with the area spectrum of the stringy charged Garfinkle-Horowitz-Strominger black hole, originating from the effective action that emerges in low-energy string theory. We find that both methods give the same results—that the area spectrum is equally spaced and does not depend on the charge $q$. Our study may provide new insights into understanding the area spectrum and entropy spectrum for stringy black holes.

We study models of late-time cosmic acceleration in terms of scalar-tensor theories generalized to include a certain class of nonlinear derivative interaction of the scalar field. The nonlinear effect suppresses the scalar-mediated force at short distances to pass solar-system tests of gravity. It is found that the expansion history until today is almost indistinguishable from that of the $\Lambda \mathrm{CDM}$ model or some (phantom) dark energy models, but the fate of the universe depends clearly on the model parameter. The growth index of matter density perturbations is computed to show that its past asymptotic value is given by $9/16$, while the value today is as small as 0.4.

We examine cosmological perturbations in a dynamical theory of inflation in which an Abelian gauge field couples directly to the inflaton, breaking conformal invariance. When the coupling between the gauge field and the inflaton takes a specific form, inflation becomes anisotropic and anisotropy can persist throughout inflation, avoiding Wald’s no-hair theorem. After discussing scenarios in which anisotropy can persist during inflation, we calculate the dominant effects of a small persistent anisotropy on the primordial gravitational wave and curvature perturbation power spectra using the “in-in” formalism of perturbation theory. We find that the primordial power spectra of cosmological perturbations gain significant direction dependence and that the fractional direction dependence of the tensor power spectrum is suppressed in comparison to that of the scalar power spectrum.

The observed angular correlation function of the cosmic microwave background has previously been reported to be anomalous, particularly when measured in regions of the sky uncontaminated by Galactic emission. Recent work by Efstathiou et al. presents a Bayesian comparison of isotropic theories, casting doubt on the significance of the purported anomaly. We extend this analysis to all anisotropic Gaussian theories with vanishing mean ($⟨\delta T⟩=0$), using the much wider class of models to confirm that the anomaly is not likely to point to new physics. On the other hand if there is any new physics to be gleaned, it results from low-$\ell$ alignments which will be better quantified by a full-sky statistic. We also consider quadratic maximum likelihood power spectrum estimators that are constructed assuming isotropy. The underlying assumptions are therefore false if the ensemble is anisotropic. Nonetheless we demonstrate that, for theories compatible with the observed sky, these estimators (while no longer optimal) remain statistically superior to pseudo-$C_{\ell }$ power spectrum estimators.