A special class of Bianchi type I expanding solutions in a string motivated theory with a single scalar field has been speculated to break the cosmic no-hair theorem that will not approach the late time isotropic expanding solution. We will show by a new perturbation approach that an unstable mode for the inflationary solutions exists when an additional phantom field is introduced. The result indicates that the existence of an unstable mode is closely related to the extra fields that could be present during the very early Universe.

We readdress the problems associated with bulk Higgs and the gauge fields in a five-dimensional Randall-Sundrum model by extending the model to six dimensions with double warping along the two extra spatial dimensions. In this six-dimensional model, we have a freedom of two moduli scales as against one modulus in the five-dimensional model. With a little hierarchy between these moduli, we can obtain the right magnitude for $W$ and $Z$ boson masses from the Kaluza-Klein modes of massive bulk gauge fields where the spontaneous symmetry breaking is triggered by bulk Higgs. We also have determined the gauge couplings of the standard model fermions with Kaluza-Klein modes of the gauge fields. Unlike the case of the five-dimensional model with a massless bulk gauge field, here, we have shown that the gauge couplings and the masses of the Kaluza-Klein gauge fields satisfy the precision electroweak constraints and also obey the Tevatron bounds.

The rich phenomena of the shear viscosity ($\eta$) to entropy density ($s$) ratio, $\eta /s$, in weakly coupled $N$-component scalar field theories are studied. $\eta /s$ can have a “double dip” behavior due to resonances and the phase transition. If an explicit Goldstone mass term is added, then $\eta /s$ can either decrease monotonically in temperature or, as seen in many other systems, reach a minimum at the phase transition. We also show how to go beyond the original variational approach to make the Boltzmann equation computation of $\eta$ systematic.

We perform a study of the standard model fit to the mixing quantities $\Delta M_{B_s}$, and $\Delta {\Gamma }_{B_s}/\Delta M_{B_s}$ in order to bound contributions of new physics (NP) to $B_s$ mixing. We then use this to explore the branching fraction of $B_s\to {\mu }^{+}{\mu }^{-}$ in certain models of NP. In most cases, this constrains NP amplitudes for $B_s\to {\mu }^{+}{\mu }^{-}$ to lie below the standard model component.

We give a theoretical framework for defining and extracting non-Abelian magnetic monopoles in a gauge-invariant way in $SU(N)$ Yang-Mills theory to study quark confinement. Then we give numerical evidences that the non-Abelian magnetic monopole defined in this way gives a dominant contribution to confinement of fundamental quarks in $SU(3)$ Yang-Mills theory, which is in sharp contrast to the $SU(2)$ case in which Abelian magnetic monopoles play the dominant role for quark confinement.

We consider the possibility of several different mechanisms contributing to the $(\beta \beta {)}_{0\nu }$-decay amplitude in the general case of $CP$ nonconservation: light Majorana neutrino exchange, heavy left-handed and heavy right-handed Majorana neutrino exchanges, lepton charge nonconserving couplings in supersymmetry theories with $R$-parity breaking. If the $(\beta \beta {)}_{0\nu }$ decay is induced by, e.g., two “noninterfering” mechanisms (light Majorana neutrino and heavy right-handed Majorana neutrino exchanges), one can determine $|{\eta }_i{|}^2$ and $|{\eta }_j{|}^2$, ${\eta }_i$ and ${\eta }_j$ being the two fundamental parameters characterizing these mechanisms, from data on the half-lives of two nuclear isotopes. In the case when two “interfering” mechanisms are responsible for the $(\beta \beta {)}_{0\nu }$ decay, $|{\eta }_i{|}^2$ and $|{\eta }_j{|}^2$ and the interference term can be uniquely determined, in principle, from data on the half-lives of three nuclei. Given the half-life of one isotope, the “positivity conditions” $|{\eta }_i{|}^2\ge 0$ and $|{\eta }_j{|}^2\ge 0$ lead to stringent constraints on the half-lives of the other $(\beta \beta {)}_{0\nu }$-decaying isotopes. These conditions, as well as the conditions for constructive (destructive) interference are derived and their implications are analyzed in two specific cases. The experimental limits on neutrino masses obtained in the ${}^{3}H$ $\beta$-decay experiments can constrain further the multiple mechanisms of $(\beta \beta {)}_{0\nu }$ decay if one of the mechanisms involved is the light Majorana neutrino exchange. The measurements of the half-lives with rather high precision and the knowledge of the relevant nuclear matrix elements with relatively small uncertainties is crucial for establishing that more than one mechanism are operative in $(\beta \beta {)}_{0\nu }$ decay. The method considered by us can be generalized to the case of more than two $(\beta \beta {)}_{0\nu }$-decay mechanisms. It allows us to treat the cases of $CP$ conserving and $CP$ nonconserving couplings generating the $(\beta \beta {)}_{0\nu }$ decay in a unique way.

We extract to high statistical precision an excited spectrum of single-particle isoscalar mesons using lattice QCD, including states of high spin and, for the first time, light exotic $J^{\mathrm{PC}}$ isoscalars. The use of a novel quark field construction has enabled us to overcome the long-standing challenge of efficiently including quark-annihilation contributions. Hidden-flavor mixing angles are extracted and while most states are found to be close to ideally flavor mixed, there are examples of large mixing in the pseudoscalar and axial sectors in line with experiment. The exotic $J^{\mathrm{PC}}$ isoscalar states appear at a mass scale comparable to the exotic isovector states.

A gauge invariant combination of LLe sleptons within the minimal supersymmetric standard model is one of the few inflaton candidates that can naturally explain population of the observable sector and creation of matter after inflation. After the end of inflation, the inflaton oscillates coherently about the minimum of its potential, which is a point of enhanced gauged symmetry. This results in bursts of nonperturbative production of the gauge/gaugino and (s)lepton quanta. The subsequent decay of these quanta is very fast and leads to an extremely efficient transfer of the inflaton energy to (s)quarks via instant preheating. Around 20% of the inflaton energy density is drained during every inflaton oscillation. However, all of the standard model degrees of freedom (and their supersymmetric partners) do not thermalize immediately, since the large inflaton vacuum expectation value breaks the electroweak symmetry. After about 100 oscillations—albeit within one Hubble time—the amplitude of inflaton oscillations becomes sufficiently small, and all of the degrees of freedom will thermalize. This provides by far the most efficient reheating of the universe with the observed degrees of freedom.

We present the first modeled search for gravitational waves using the complete binary black-hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data, taken between November 2005 and September 2007, for systems with component masses of $1–99M_{\odot }$ and total masses of $25–100M_{\odot }$. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for $19M_{\odot }\le m_1$, $m_2\le 28M_{\odot }$ binary black-hole systems with negligible spin to be no more than $2.0{\mathrm{Mpc}}^{-3}{\mathrm{Myr}}^{-1}$ at 90% confidence.

We search the COSMOS survey for pairs of galaxies consistent with the gravitational lensing signature of a cosmic string. The COSMOS survey imaged 1.64 square degrees using the Advanced Camera for Surveys aboard the Hubble Space Telescope. Our technique includes estimates of the efficiency for finding the lensed galaxy pair. We find no evidence for cosmic strings with a mass per unit length of $G\mu /c^2<3.0\times {10}^{-7}$ out to redshifts greater than 0.6 and set 95% upper limits. This corresponds to a global 95% upper limit of ${\Omega }_{\mathrm{strings}}<0.0028$.

Recently, Tevatron released their measurements on the invariant mass spectrum of electron and positron, as well as the dijet arising from $WW+WZ$ production, with one $W$ decaying leptonically. Although the statistics are not significant, there are two bumps around 240 GeV and 120–160 GeV, respectively. We proposed that the two bumps correspond to the extra-light gauge bosons $Z^{\prime }$ and $W^{\prime }$, which couple with quarks with deci-weak strength. In this brief report, we also simulated dijet invariant mass distribution at the current running LHC.

We study the radiative decay properties of the charmoniumlike $X$, $Y$, and $Z$ mesons generated dynamically from vector-meson–vector-meson interaction in the framework of a unitarized hidden-gauge formalism. In the present work, we calculate the one- and two-photon decay widths of the hidden-charm $Y(3940)$, $Z(3930)$ [or $X(3915)$], and $X(4160)$ mesons in the framework of the vector-meson dominance formalism. We obtain good agreement with the experiment in case of the two-photon width of the $X(3915)$, which we associate to the $2^{+}$ resonance that we find at 3922 MeV. However, in view of discrepancies with a different approach that also considers the resonances as molecular states, we urge independent calculations along the same lines to further clarify the issue.

We derive a “master formula” for the contribution of the three-gluon correlation function in the nucleon to the twist-3 single-spin-dependent cross section for semi-inclusive deep-inelastic scattering, $e{p}^{\uparrow }\to eDX$. This is an extension of the similar formula known for the so-called soft-gluon-pole contribution induced by the quark-gluon correlation function in a variety of processes. Our master formula reduces the relevant interfering partonic subprocess with the participation of the three gluons to the Born cross sections for the ${\gamma }^{*}g\to c\overline{c}$ scattering, which reveals the new structure behind the twist-3 single spin asymmetry and simplifies the actual calculation greatly. A possible extension to higher order corrections is also discussed.

Using the AdS/CFT correspondence, we study the hydrodynamics with conserved current from the dual Maxwell-Gauss-Bonnet gravity. After constructing the perturbative solution to the first order based on the boosted black brane solution in the bulk Maxwell-Gauss-Bonnet gravity, we extract the stress tensor and conserved current of the dual conformal fluid on its boundary, and also find the effect of the Gauss-Bonnet term on the dual conformal fluid. Our results show that the Gauss-Bonnet term can affect the parameters such as the shear viscosity $\eta$, entropy density $s$, thermal conductivity $\kappa$ and electrical conductivity $\sigma$. However, it does not affect the so-called Wiedemann-Franz law which relates $\kappa$ to $\sigma$, while it affects the ratio $\eta /s$. In addition, another interesting result is that $\eta /s$ can also be affected by the bulk Maxwell field in our case, which is consistent with some previous results predicted through the Kubo formula. Moreover, the anomalous magnetic and vortical effects by adding the Chern-Simons term are also considered in our case in the Maxwell-Gauss-Bonnet gravity.

We expand on the results of our recent letter [Phys. Rev. Lett. 106, 091601 (2011)], where we presented new recursion relations for correlation functions of the stress-tensor and conserved currents in conformal field theories with an ${\mathrm{AdS}}_{d+1}$ dual for $d\ge 4$. These recursion relations are derived by generalizing the Britto-Cachazo-Feng-Witten (BCFW) relations to amplitudes in anti-de Sitter space (AdS) that are dual to boundary correlators, and are usually computed perturbatively by Witten diagrams. Our results relate vacuum-correlation functions to integrated products of lower-point transition amplitudes, which correspond to correlators calculated between states dual to certain normalizable modes. We show that the set of “polarization vectors” for which amplitudes behave well under the BCFW extension is smaller than in flat-space. We describe how transition amplitudes for more general external polarizations can be constructed by combining answers obtained by different pairs of BCFW shifts. We then generalize these recursion relations to supersymmetric theories. In AdS, unlike flat-space, even maximal supersymmetry is insufficient to permit the computation of all correlators of operators in the same multiplet as a stress-tensor or conserved current. Finally, we work out some simple examples to verify our results.

We consider the one-loop quantum corrections to the Nielsen-Olesen flux tube of finite length $L$, by imposing periodic boundary conditions. The calculations are based on a recent evaluation of these quantum corrections to the string tension of an infinite vortex. The finite length corrections are finite from the outset. If the computation is restricted to the zero modes we obtain the standard Lüscher term $\pi /3L$ for a closed string. The inclusion of the other fluctuation modes of Higgs and gauge fields, using the numerically computed trace of the Euclidian Green’s function, leads to corrections that decrease exponentially with $L$. We present numerical results for these corrections, and discuss their possible relevance and the limitations of the approach.

Formalism of extended Lagrangian represents a systematic procedure to look for the local symmetries of a given Lagrangian action. In this work, the formalism is discussed and applied to a field theory. We describe it in detail for a field theory with first-class constraints present in the Hamiltonian formulation. The method is illustrated on examples of electrodynamics, Yang-Mills field, and nonlinear sigma model.

In a wide class of direct and semidirect gauge mediation models, it has been observed that the gaugino masses vanish at leading order. It implies that there is a hierarchy between the gaugino and sfermion masses, invoking a fine-tuning problem in the Higgs sector via radiative corrections. In this paper, we explore the possibility of solving this anomalously light gaugino problem exploiting strong conformal dynamics in the hidden sector. With a mild assumption on the anomalous dimensions of the hidden sector operators, we show that the next-to-leading order contributions to the gaugino masses can naturally be in the same order as the sfermion masses. The $\mu /B_{\mu }$ problem is also discussed.

We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value $n_T$ and the Fermi momentum $k_F<\sqrt{\frac{3}{2}}m$ that depends on the tachyon mass $m$. The pressure $P$ and energy density $E$ cannot be arbitrary small, but the situation $P>E$ is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density $n_T<n<3.45n_T$ the tachyon matter remains stable but no shock wave survives.

Asymptotically flat wormhole solutions are found in the deformed Hořava-Lifshitz gravity. It turns out that higher curvature terms cannot play the role of exotic matters which are crucial to form a traversable wormhole, and external exotic sources are still needed. In particular, the exotic matter behaves like phantom energy if the Kehagias-Sfetsos vacuum is considered outside the wormhole. Interestingly, the spherically symmetric setting makes the matter and the higher curvature contribution satisfy four-dimensional conservation of energy in the covariant form.