We calculate modifications to the scalar Casimir force between two parallel plates due to space-time noncommutativity. We devise a heuristic approach to overcome the difficulties of describing boundaries in noncommutative theories and predict that boundary corrections are of the same order as noncommutative volume corrections. Further, both corrections have the form of more conventional finite surface effects.

We study the phase diagrams of $N=\infty$ vectorlike, asymptotically free gauge theories as a function of volume, on $S^3\times S^1$. The theories of interest are the ones with fermions in two index representations [adjoint, (anti)symmetric, and bifundamental abbreviated as QCD(adj), QCD(AS/S), and QCD(BF)], and are interrelated via orbifold or orientifold projections. The phase diagrams reveal interesting phenomena such as disentangled realizations of chiral and center symmetry, confinement without chiral symmetry breaking, zero temperature chiral transitions, and in some cases, exotic phases which spontaneously break the discrete symmetries such as $C$, $P$, $T$ as well as $CPT$. In a regime where the theories are perturbative, the deconfinement temperature in SYM, and QCD(AS/S/BF) coincide. The thermal phase diagrams of thermal orbifold QCD(BF), orientifold QCD(AS/S), and $\mathcal{N}=1$ SYM coincide, provided charge conjugation symmetry for QCD(AS/S) and ${\mathbb{Z}}_2$ interchange symmetry of the QCD(BF) are not broken in the phase continuously connected to the ${\mathbb{R}}^4$ limit. When the $S^1$ circle is endowed with periodic boundary conditions, the (nonthermal) phase diagrams of orbifold and orientifold QCD are still the same, however, both theories possess chirally symmetric phases which are absent in $\mathcal{N}=1$ SYM. The match and mismatch of the phase diagrams depending on the spin structure of fermions along the $S^1$ circle is naturally explained in terms of the necessary and sufficient symmetry realization conditions which determine the validity of the nonperturbative orbifold-orientifold equivalence.

We present improved post-Newtonian-inspired initial data for nonspinning black-hole binaries, suitable for numerical evolution with punctures. We revisit the work of Tichy et al. [W. Tichy, B. Brügmann, M. Campanelli, and P. Diener, Phys. Rev. D 67, 064008 (2003).], explicitly calculating the remaining integral terms. These terms improve accuracy in the far zone and, for the first time, include realistic gravitational waves in the initial data. We investigate the behavior of these data both at the center of mass and in the far zone, demonstrating agreement of the transverse-traceless parts of the new metric with quadrupole-approximation waveforms. These data can be used for numerical evolutions, enabling a direct connection between the merger waveforms and the post-Newtonian inspiral waveforms.

We study the consequences of a homogeneous dark energy fluid having a nonvanishing velocity with respect to the matter and radiation large-scale rest frames. We consider homogeneous anisotropic cosmological models with four fluids (baryons, radiation, dark matter, and dark energy) whose velocities can differ from each other. Performing a perturbative calculation up to second order in the velocities, we obtain the contribution of the anisotropies generated by the fluids motion to the CMB quadrupole and compare with observations. We also consider the exact problem for arbitrary velocities and solve the corresponding equations numerically for different dark energy models. We find that models whose equation of state is initially stiffer than radiation, as for instance some tracking models, are unstable against velocity perturbations, thus spoiling the late-time predictions for the energy densities. In the case of scaling models, the contributions to the quadrupole can be non-negligible for a wide range of initial conditions. We also consider fluids moving at the speed of light (null fluids) with positive energy and show that, without assuming any particular equation of state, they generically act as a cosmological constant at late times. We find the parameter region for which the models considered could be compatible with the measured (low) quadrupole.

In the frameworks of the littlest Higgs (LH) model and its extension with T parity (LHT), we studied the associated $t\overline{t}{h}^0$ production process $e^{+}{e}^{-}\to \gamma \gamma \to t\overline{t}{h}^0$ at the future $e^{+}{e}^{-}$ linear colliders up to QCD next-to-leading order. We present the regions of $\sqrt{s}-f$ parameter space in which the LH and LHT effects can and cannot be discovered with the criteria assumed in this paper. The production rates of process $\gamma \gamma \to t\overline{t}{h}^0$ in different photon polarization collision modes are also discussed. We conclude that one could observe the effects contributed by the LH or LHT model on the cross section for the process $e^{+}{e}^{-}\to \gamma \gamma \to t\overline{t}{h}^0$ in a reasonable parameter space, or might put more stringent constraints on the $\mathrm{LH}/\mathrm{LHT}$ parameters in the future experiments at linear colliders.

We investigate the possibility of a dark matter candidate emerging from a minimal walking technicolor theory. In this case, techniquarks as well as technigluons transform under the adjoint representation of SU(2) of technicolor. It is therefore possible to have technicolor neutral bound states between a techniquark and a technigluon. We investigate this scenario by assuming that such a particle can have a Majorana mass and we calculate the relic density. We identify the parameter space where such an object can account for the full dark matter density avoiding constraints imposed by the CDMS and the LEP experiments.

We propose a new model for describing baryon semileptonic decays for estimating $F$ and $D$ values with explicit breaking effects of both SU(3) and SU(2) flavor symmetry, where all possible SU(3) and SU(2) breaking effects are induced from an effective interaction. An overall fit including the weak magnetism form factor yields $F=0.477\pm 0.001$, $D=0.835\pm 0.001$, $V_{ud}=0.975\pm 0.002$, and $V_{us}=0.221\pm 0.002$ with ${\chi }^2=4.43/5\mathrm{d}.\mathrm{o}.\mathrm{f}.$. The spin content of strange quarks $\Delta s$ is estimated from the obtained values $F$ and $D$, and the nucleon spin problem is reexamined. Furthermore, the unmeasured values of $(g_1/f_1)$ and $(g_1)$ for other hyperon semileptonic decays are predicted from this new formula.

We report a measurement of $CP$-violating asymmetries in $B^0\to (\rho \pi {)}^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays using a time-dependent Dalitz plot analysis. The results are obtained from a data sample of $375\times {10}^6$ $\mathit{{\rm Y}}(4S)\to B\overline{B}$ decays, collected by the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We measure 26 coefficients of the bilinear form-factor terms occurring in the time-dependent decay rate of the $B^0$ meson. We derive the physically relevant quantities from these coefficients. In particular, we measure a constraint on the angle $\alpha$ of the unitarity triangle.

We prove that a twist-3 soft-gluon-pole (SGP) cross section for single spin asymmetries is determined by a certain “primordial” twist-2 cross section up to kinematic and color factors in the leading order perturbative QCD. In particular, for the processes in which the partonic hard scattering occurs among massless partons, the invariance of the primordial partonic cross section under scale transformation leads to remarkable simplification of the SGP cross section, reproducing the compact form that was recently observed for pion production $p^{\uparrow }p\to \pi X$ and direct-photon production $p^{\uparrow }p\to \gamma X$.

Using the formalism that separates the contributions of vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy, we show that a two-level atom in interaction with a quantum massless scalar field both in the Hartle-Hawking and Unruh vacuum in a $1+1$ dimensional black hole background spontaneously excites as if there is thermal radiation at the Hawking temperature emanating from the black hole. Our calculation, therefore, ties the existence of Hawking radiation to the spontaneous excitation of a two-level atom placed in vacuum in the exterior of a black hole and shows pleasing consistence of two different physical phenomena, the Hawking radiation and the spontaneous excitation of atoms, which are quite prominent in their own right.

In this note, we construct a Becchi-Rouet-Stora-Tyutin (BRST) invariant cubic vertex for massless fields of arbitrary mixed symmetry in flat space-time. The construction is based on the vertex given in bosonic open string field theory. The algebra of gauge transformations is closed without any additional, higher than cubic, couplings due to the presence of an infinite tower of massless fields. We briefly discuss the generalization of this result to a curved space-time and other possible implications.

Quantum gravitational effects in loop quantum cosmology lead to a resolution of the initial singularity and have the potential to solve the horizon problem and generate a quasi scale-invariant spectrum of density fluctuations. We consider loop modifications to the behavior of the inverse scale factor below a critical scale in closed models and assume a purely thermal origin for the fluctuations. We show that the no-go results for scale invariance in classical thermal models can be evaded even if we just consider modifications to the background (zeroth order) gravitational dynamics. Since a complete and systematic treatment of the perturbed Einstein equations in loop cosmology is still lacking, we simply parametrize their expected modifications. These change quantitatively, but not qualitatively, our conclusions. We thus urge the community to more fully work out this complex aspect of loop cosmology, since the full picture would not only fix the free parameters of the theory, but also provide a model for a noninflationary, thermal origin for the structures of the Universe.

In this paper we examine the IR inflation scenario using the Dirac-Born-Infeld action, where we have $N$ multiple branes located near the tip of a warped geometry. At large $N$ the solutions are similar in form to the more traditional single brane models; however, we find that it is difficult to simultaneously satisfy the Wilkinson Microwave Anisotropy Probe bounds on the scalar amplitude and the scalar spectral index. We go on to examine two new solutions where $N=2$ and $N=3$, respectively, which both have highly nonlinear actions. The sound speed in both cases is dramatically different from previous works, and for the $N=3$ case it can actually be zero. We show that inflation is possible in both frameworks, and find that the scalar spectral index is bounded from above by unity. The levels of non-Gaussian fluctuations are smaller in the $N=2$ case compared to the single brane models, while those in the $N=3$ case are much larger.

We compute the neutralino direct detection rate in nonstandard cosmological scenarios where neutralinos account for the dark matter of the Universe. Significant differences are found when such rates are compared with those predicted by the standard cosmological model. For $b$-ino-like neutralinos, the main feature is the presence of additional light ($m_{\chi }\lesssim 40\mathrm{GeV}$) and heavy ($m_{\chi }\gtrsim 600\mathrm{GeV}$) neutralinos with detection rates within the sensitivity of future dark matter experiments. For Higgsino-like and $W$-ino-like neutralinos lighter than $m_{\chi }\sim 1\mathrm{TeV}$, enhancements of more than 2 orders of magnitude in the largest detection rates are observed. Thus, if dark matter is made up of neutralinos, the prospects for their direct detection are in general more promising than in the standard cosmology.

At the LHC, ${\tilde{q}}_L{\tilde{q}}_L$ production is one of the main supersymmetry production processes in the minimal supersymmetric standard model (MSSM), which occurs due to the chirality flip caused by the Majorana gluino mass. This process is one of the sources of same sign two lepton ($\mathrm{SS}2l$) events; however, gluino production also contributes to this channel. In this paper, we develop a method to identify gluino and squark production separately in the $\mathrm{SS}2l$ channel, based on cuts on the kinematical configuration of the jets. We applied the method to the MSSM, a model with an extended gluino sector, and the littlest Higgs model with $T$ parity and found a distinctive difference between these models when considering the numbers of $\mathrm{SS}2l$ events selected by the cuts.

We discuss and compare the effects of one extra dimension in the Randall-Sundrum models on the evaluation of the Casimir force between two parallel plates. We impose the condition that the result reproduce the experimental measurements within the known uncertainties in the force and the plate separation, and get an upper bound $kR\lesssim 20$ if the curvature parameter $k$ of ${\mathrm{AdS}}_5$ is equal to the Planck scale. Although the upper bound decreases as $k$ decreases, $kR\sim 12$, which is the required value for solving the hierarchy problem, is consistent with the Casimir force measurements. For the case where the 5th dimension is infinite, the correction to the Casimir force is very small and negligible.

We consider an effective model of photon interaction with a scalar field corresponding to conformal excitations of the internal space (geometrical moduli/gravexcitons). We demonstrate that this interaction results in a modified dispersion relation for photons, and, consequently, the photon group velocity depends on the energy implying the propagation time-delay effect. We suggest the use of the experimental bounds of the time delay of gamma-ray burst photon propagation as an additional constraint for the gravexciton parameters.

We show that when a model, which is equivalent to the Gürsey model classically, is gauged with a $\mathrm{SU}(N)$ field, we get indications of a nontrivial field theory.