There is a subtle difference between the open string dynamics determined by the original dual resonance models and that determined by D-brane constructions within critical closed string theory. For instance, in contrast to the former, the latter have massless scalars in addition to the massless gluon shared by both. We introduce and explain the concept of non-Abelian D-branes, which illuminates this distinction. We employ this concept to offer new possibilities for string duals for large $N$ QCD (pure Yang-Mills gauge theory).

We discuss corrections to the Yukawa matrices of the standard model (SM) fermions in intersecting D-brane models due to four-point interactions. Recently, an intersecting D-brane model has been found where it is possible to obtain correct masses and mixings for all quarks as well as the tau lepton. However, the masses for the first two charged leptons come close to the right values but are not quite correct. Since the electron and muon are quite light, it is likely that there are additional corrections to their masses which cannot be neglected. With this in mind, we consider contributions to the SM fermion mass matrices from four-point interactions. In an explicit model, we show that it is indeed possible to obtain the SM fermion masses and mixings which are a better match to those resulting from experimental data extrapolated at the unification scale when these corrections are included. These corrections may have broader application to other models.

A dark energy scalar (or a function of the Ricci scalar) coupled with the derivative to the matter fields will violate the $CPT$ symmetry during the expansion of the Universe. This type of cosmological $CPT$ violation helps to generate the baryon number asymmetry and gives rise to the rotation of the photon polarization which can be measured in the astrophysical and cosmological observations, especially the experiments of the cosmic microwave background radiation. In this paper, we derive the rotation angle in a fully general relativistic way and present the rotation formulas used for the cosmic microwave background data analysis. Our formulas include the corrections from the spatial fluctuations of the scalar field. We also estimate the magnitude of these corrections in a class of dynamical dark energy models for quintessential baryo/leptogenesis.

Gravitational particle production in the context of braneworlds is considered from a phenomenological point of view. The production of Kaluza-Klein modes for bulk fields is discussed and their abundances computed. The results have been applied to some specific fields such as gravitinos and axions, and their cosmologies have been outlined, exemplifying the constraints on the properties of the extra dimensional model in each case.

Within the framework of nonstandard (Weyl) representations of the canonical commutation relations, we investigate the polymer quantization of the Taub cosmological model. The Taub model is analyzed within the Arnowitt-Deser-Misner reduction of its dynamics, by which a time variable arises. While the energy variable and its conjugate momentum are treated as ordinary Heisenberg operators, the anisotropy variable and its conjugate momentum are represented by the polymer technique. The model is analyzed at both classical and quantum level. As a result, classical trajectories flatten with respect to the potential wall, and the cosmological singularity is not probabilistically removed. In fact, the dynamics of the wave packets is characterized by an interference phenomenon, which, however, is not able to stop the evolution towards the classical singularity.

In the general matter composition where the multiple scalar fields and the multiple perfect fluids coexist, in the leading order of the gradient expansion, we construct all of the solutions of the nonlinear evolutions of the locally homogeneous universe. From the momentum constraint, we derive the constraints which the solution constants of the locally homogeneous universe must satisfy. We construct the gauge invariant perturbation variables in the arbitrarily higher order nonlinear cosmological perturbation theory around the spatially flat Friedmann-Robertson-Walker universe. We construct the nonlinear long wavelength limit formula representing the long wavelength limit of the evolution of the nonlinear gauge invariant perturbation variables in terms of perturbations of the evolutions of the locally homogeneous universe. By using the long wavelength limit formula, we investigate the evolution of nonlinear cosmological perturbations in the universe dominated by the multiple slow rolling scalar fields with an arbitrary potential. The $\tau$ function and the $N$ potential introduced in this paper make it possible to write the evolution of the multiple slow rolling scalar fields with an arbitrary interaction potential and the arbitrarily higher order nonlinear Bardeen parameter at the end of the slow rolling phase analytically. It is shown that the nonlinear parameters such as $f_{\mathrm{NL}}$ and $g_{\mathrm{NL}}$ are suppressed by the slow rolling expansion parameters.

We consider the conditions for integrating out heavy chiral fields and moduli in $\mathcal{N}=1$ supergravity, subject to two explicit requirements. First, the expectation values of the heavy fields should be unaffected by low energy phenomena. Second, the low energy effective action should be described by $\mathcal{N}=1$ supergravity. This leads to a working definition of decoupling in $\mathcal{N}=1$ supergravity that is different from the usual condition of gravitational strength couplings between sectors, and that is the relevant one for inflation with moduli stabilization, where some light fields (the inflaton) can have long excursions in field space. It is also important for finding de Sitter vacua in flux compactifications such as LARGE volume and Kachru-Kallosh-Linde-Trivedi (KKLT) scenarios, since failure of the decoupling condition invalidates the implicit assumption that the stabilization and uplifting potentials have a low energy supergravity description. We derive a sufficient condition for supersymmetric decoupling, namely, that the Kähler invariant function $G=K+\log |W{|}^2$ is of the form $G=L(\mathrm{\text{light}},H(\mathrm{\text{heavy}}))$ with $H$ and $L$ arbitrary functions, which includes the particular case $G=L(\mathrm{\text{light}})+H(\mathrm{\text{heavy}})$. The consistency condition does not hold in general for the ansatz $K=K(\mathrm{\text{light}})+K(\mathrm{\text{heavy}})$, $W=W(\mathrm{\text{light}})+W(\mathrm{\text{heavy}})$ and we discuss under what circumstances it does hold.

A class of extra dimensional models with a warped metric predict tunneling of a massive particle localized on our brane and escaping into additional dimensions. The experimental signature of this effect is the disappearance of the particle from our world, i.e. the particle invisible decay. We point out that measurements of $Z^{\prime }\to \mathrm{\text{invisible}}$ decay width of a new heavy gauge boson $Z^{\prime }$ at the CERN LHC can be used to probe the existence of large extra dimensions. This result enhances motivations for a more sensitive search and study for this decay mode and suggests an additional direction for testing extra dimensions in collider experiments.

The Schwinger mechanism, the production of charged particle-antiparticle pairs in a macroscopic external electric field, is derived for $2+1$-dimensional theories. The rate of pair production per unit area for four species of massless fermions, with charge $q$, in a constant electric field $E$ is given by ${\pi }^{-2}{\hslash }^{-3/2}{\tilde{c}}^{-1/2}(qE{)}^{3/2}$ where $\tilde{c}$ is the speed of light for the two-dimensional system. To the extent undoped graphene behaves like the quantum field-theoretic vacuum for massless fermions in $2+1$ dimensions, the Schwinger mechanism should be testable experimentally. A possible experimental configuration for this is proposed. Effects due to deviations from this idealized picture of graphene are briefly considered. It is argued that with present day samples of graphene, tests of the Schwinger formula may be possible.

The littlest Higgs model with $T$ parity (called the LHT model) predicts the existence of the $T$-odd leptons, which can generate contributions to some leptonic processes at the one-loop level. We calculate their contributions to the leptonic $Z$ decay processes $Z\to l{\overline{l}}^{\prime }$, $Z\to l\overline{l}$, and $Z\to \nu \overline{\nu }$. We find that the $T$-odd leptons can give significant contributions to the branching ratios of these decay processes in most of the parameter space. The experimental measurement values might generate constraints on the free parameters of the LHT model.

We calculate results for $K\to \pi$ and $K\to 0$ matrix elements to next-to-leading order in $2+1$ flavor partially quenched chiral perturbation theory. Results are presented for both the $\Delta I=1/2$ and $3/2$ channels, for chiral operators corresponding to current-current, gluonic penguin, and electroweak penguin 4-quark operators. These formulas are useful for studying the chiral behavior of currently available $2+1$ flavor lattice QCD results, from which the low-energy constants of the chiral effective theory can be determined. The low-energy constants of these matrix elements are necessary for an understanding of the $\Delta I=1/2$ rule, and for calculations of ${ϵ}^{\prime }/ϵ$ using current lattice QCD simulations.

We compute the $\mathcal{O}({\alpha }_s)$ QCD corrections to charged triple vector boson production at a hadron collider, i.e., the processes $pp\to ZZ{W}^{\pm }+X$ and $pp\to W^{\pm }{W}^{\mp }{W}^{\pm }+X$. Intermediate Higgs boson exchange effects, spin correlations from leptonic vector boson decays, and off shell contributions are all taken into account. Results are implemented in a fully flexible Monte Carlo program that allows for an easy customization of kinematical cuts and variation of the factorization and renormalization scales. We analyze the dependence of the differential cross sections under scale variations and present distributions where the QCD corrections strongly modify the leading-order results.

Neutrino fluxes at telescopes depend on both initial fluxes out of astronomical bursts and flavor mixing during their travel to the Earth. However, since the information on the initial composition requires better precision in mixing angles and vice versa, neutrino detection at telescopes cannot provide solutions to both problems by itself. Thus, a probability to be measured at long-baseline oscillation is considered as a complement to the telescope, and problems like source identification and parameter degeneracy are examined under a few assumptions.

Using ${\rm Y}(2S)$ and ${\rm Y}(3S)$ data collected with the CLEO III detector we have searched for decays of ${\chi }_{bJ}$ to final states with open charm. We fully reconstruct $D^0$ mesons with $p_{D^0}>2.5\mathrm{GeV}/c$ in three decay modes ($K^{-}{\pi }^{+}$, $K^{-}{\pi }^{+}{\pi }^0$, and $K^{-}{\pi }^{-}{\pi }^{+}{\pi }^{+}$) in coincidence with radiative transition photons that tag the production of one of the ${\chi }_{bJ}(nP)$ states. Significant signals are obtained for the two $J=1$ states. Recent nonrelativistic QCD (NRQCD) calculations of ${\chi }_{bJ}(nP)\to c\overline{c}X$ depend on one nonperturbative parameter per ${\chi }_{bJ}$ triplet. The extrapolation from the observed $D^{0}X$ rate over a limited momentum range to a full $c\overline{c}X$ rate also depends on these same parameters. Using our data to fit for these parameters, we extract results which agree well with NRQCD predictions, confirming the expectation that charm production is largest for the $J=1$ states. In particular, for $J=1$, our results are consistent with $c\overline{c}g$ accounting for about one-quarter of all hadronic decays.

In critical phenomena, singular behaviors arise not only for thermodynamic quantities but also for transport coefficients. We study this dynamic critical phenomenon in the AdS/CFT duality. We consider black holes with a single R-charge in various dimensions and compute the R-charge diffusion in the linear perturbations. In this case, the black holes belong to model B according to the classification of Hohenberg and Halperin.

We investigate in more detail the holographic model of a superconductor recently found by Hartnoll, Herzog, and Horowitz [Phys. Rev. Lett. 101, 031601 (2008)], which is constructed from a condensate of a charged scalar field in ${\mathrm{AdS}}_4$-Schwarzschild background. By analytically studying the perturbation of the gravitational system near the critical temperature $T_c$, we obtain the superconducting coherence length proportional to $1/\sqrt{1-T/T_c}$ via AdS/CFT (anti–de Sitter/conformal field theory) correspondence. By adding a small external homogeneous magnetic field to the system, we find that a stationary diamagnetic current proportional to the square of the order parameter is induced by the magnetic field. These results agree with Ginzburg-Landau theory and strongly support the idea that a superconductor can be described by a charged scalar field on a black hole via AdS/CFT duality.

In this work, we calculate the classical solutions for the electrodynamics stemming from the Lorentz-violating (LV) and $CPT$-even term of the standard model extension. Static and stationary solutions for pointlike and extended charges are obtained from the wave equations by means of the Green method. A dipolar expansion is written for the field strengths. It is explicitly shown that charge and current generate LV first order effects for the magnetic and electric fields, respectively. Using the magnetic field generated by a macroscopic $1C$ charged sphere, we establish a stringent bound for the LV parameter: $\kappa \le {10}^{-16}$.

We use the evolution operator method to find the one-loop effective action of scalar and spinor QED in electric field backgrounds in terms of the Bogoliubov coefficient between the ingoing and the outgoing vacua. We obtain the exact one-loop effective action for a Sauter-type electric field, $E_0{\mathrm{sech}}^2(t/\tau )$, and show that the imaginary part correctly yields the vacuum persistence. The renormalized effective action shows the general relation between the vacuum persistence and the total mean number of created pairs for the constant and the Sauter-type electric field.

We discuss thermodynamic properties of dark energy using the formalism of field theory at finite temperature. In particular, we apply our formalism to a purely kinetic type of k-essence. We show quite generally that the entropy associated with dark energy is always equal or greater than zero. Hence, contrary to often stated claims, a violation of the null energy condition (phantom dark energy) does not necessarily yield a negative entropy. In addition, we find that the thermal fluctuations of a k-essence field may be represented by a free boson gas with an effective number of degrees of freedom equal to $c_s^{-3}$.

We present a code for solving the coupled Einstein-hydrodynamics equations to evolve relativistic, self-gravitating fluids. The Einstein field equations are solved in generalized harmonic coordinates on one grid using pseudospectral methods, while the fluids are evolved on another grid using shock-capturing finite difference or finite volume techniques. We show that the code accurately evolves equilibrium stars and accretion flows. Then we simulate an equal-mass nonspinning black hole-neutron star binary, evolving through the final four orbits of inspiral, through the merger, to the final stationary black hole. The gravitational waveform can be reliably extracted from the simulation.