We investigate the behavior of tensor fluctuations in Loop Quantum Cosmology, focusing on a class of scaling solutions which admit a near scale-invariant scalar field power spectrum. We obtain the spectral index of the gravitational field perturbations, and find a strong blue tilt in the power spectrum with $n_t\approx 2$. The amplitude of tensor modes are, therefore, suppressed by many orders of magnitude on large scales compared to those predicted by the standard inflationary scenario where $n_t\approx 0$.

Near the horizon of a black brane solution in anti-de Sitter space, the long-wavelength fluctuations of the metric exhibit hydrodynamic behavior. For Einstein’s theory, the ratio of the shear viscosity of near-horizon metric fluctuations $\eta$ to the entropy per unit of transverse volume $s$ is $\eta /s=1/4\pi$. We propose that, in generalized theories of gravity, this ratio is given by the ratio of two effective gravitational couplings and can be different than $1/4\pi$. Our proposal confirms that $\eta /s$ is equal to $1/4\pi$ for any theory that can be transformed into Einstein’s theory, such as $F(R)$ gravity. Our proposal also implies that matter interactions—except those including explicit or implicit factors of the Riemann tensor—will not modify $\eta /s$. The proposed formula reproduces, in a very simple manner, some recently found results for Gauss-Bonnet gravity. We also make a prediction for $\eta /s$ in Lovelock theories of any order or dimensionality.

In this work we calculate the leading electroweak (EW) corrections to the anomalous $gt\overline{t}$ coupling in the littlest Higgs model with T-parity, by applying the Goldstone boson equivalence theorem. In the littlest Higgs model with T-parity model, such electroweak corrections arise from the loop diagrams of heavy fermions and the “would-be” Goldstone bosons. We further examine the EW corrections in the top quark pair production via the quark annihilation process at the LHC. The negative EW corrections in the standard model are partially canceled by the positive EW corrections from the loops of the new heavy particles, and the latter dominates in the large invariant mass of the top quark pair.

The scalar susceptibility (${\chi }_s$) of QCD, which represents the response of the chiral condensate to a small perturbation of explicit chiral-symmetry breaking ($m\ne 0$), is investigated within the nonlocal chiral quark model ($\mathrm{NL}\chi \mathrm{QM}$) based on the instanton vacuum configuration for $N_f=2$. We also take into account $1/N_c$ meson-loop (ML) corrections including scalar and pseudoscalar mesons. It turns out that the chiral condensate is modified to a large extend by the ML corrections in the vicinity of $m=0$, whereas its effect becomes weak beyond $m\approx 100\mathrm{MeV}$. As numerical results, we find that ${\chi }_s=-0.34{\mathrm{GeV}}^2$ with the ML corrections and $0.18{\mathrm{GeV}}^2$ without it. From these observations, we conclude that the ML corrections play an important role in the presence of finite current-quark mass.

Based on the dynamical equations for a nonrotating elastic deformable astronomical body in the first post-Newtonian approximation of Einstein’s theory of gravity, we re-examined the boundary(junction) conditions and have proven that a term, which is missing in the customary boundary(junction) conditions, is found. This term is induced by the existence of initial equilibrium hydrostatic pressure. A physical explanation of this term is given in the Newtonian approximation as well. By using the correcting boundary conditions the relation of the free spherically symmetrical radial oscillation frequency of a nonrotating homogeneously and isotropically elastic sphere with constant density is derived.

In this paper it is shown how to obtain the simplest equations for the Mukhanov-Sasaki variables describing quantum linear scalar perturbations in the case of scalar fields without potential term. This was done through the implementation of canonical transformations at the classical level, and unitary transformations at the quantum level, without ever using any classical background equation, and it completes the simplification initiated in investigations by Langlois [D. Langlois, Classical Quantum Gravity 11, 389 (1994).], and Pinho and Pinto-Neto [E. J. C. Pinho and N. Pinto-Neto, Phys. Rev. D 76, 023506 (2007).] for this case. These equations were then used to calculate the spectrum index $n_s$ of quantum scalar perturbations of a nonsingular inflationary quantum background model, which starts at infinity past from flat space-time with Planckian size spacelike hypersurfaces, and inflates due to a quantum cosmological effect, until it makes an analytical graceful exit from this inflationary epoch to a decelerated classical stiff matter expansion phase. The result is $n_s=3$, incompatible with observations.

We investigate ${\mathrm{B}}_3$ minimal supergravity models, where the lightest stau ${\tilde{\tau }}_1$ is the lightest supersymmetric particle. ${\mathrm{B}}_3$ models allow for lepton number and R-parity violation; the lightest supersymmetric particle can thus decay. We assume one nonzero ${\mathrm{B}}_3$ coupling ${\lambda }_{ijk}^{\prime }$ at $M_{\mathrm{GUT}}$, which generates further ${\mathrm{B}}_3$ couplings at $M_Z$. We study the renormalization group equations and give numerical examples. The new couplings lead to additional ${\tilde{\tau }}_1$ decays, providing distinct collider signatures. We classify the ${\tilde{\tau }}_1$ decays and describe their dependence on the minimal supergravity parameters. We exploit our results for single slepton production at the LHC. As an explicit numerical example, we investigate single-smuon production, focussing on like-sign dimuons in the final state. Also considered are final states with three or four muons.

Motivated by the observation of neutrino oscillations, we extend the Higgs boson exempt no-scale supersymmetry model by adding three heavy right-handed neutrino chiral supermultiplets to generate the light neutrino masses and mixings. The neutrino Yukawa couplings can induce new lepton-flavor violating couplings among the soft terms in the course of renormalization group running down from the boundary scale. We study the effects this has on the predictions for low-energy probes of lepton-flavor violation (LFV). Heavy right-handed neutrinos also provide a way to generate the baryon asymmetry through leptogenesis. We find that consistency with LFV and leptogenesis puts strong requirements on either the form of the Yukawa mass matrix or the smallness of the Higgs up soft mass. In all cases, we generically expect that new physics LFV is nonzero and can be found in a future experiment.

We compute in order ${\alpha }_s$ the nonrelativistic QCD (NRQCD) short-distance coefficients that match quark-antiquark operators of all orders in the heavy-quark velocity $v$ to the electromagnetic current. We employ a new method to compute the one-loop NRQCD contribution to the matching condition. The new method uses full-QCD expressions as a starting point to obtain the NRQCD contribution, thus greatly streamlining the calculation. Our results show that, under a mild constraint on the NRQCD operator matrix elements, the NRQCD velocity expansion for the quark-antiquark-operator contributions to the electromagnetic current converges. The velocity expansion converges rapidly for approximate $J/\psi$ operator matrix elements.

A measurement of the ratio $R_{{\chi }_c}=({\chi }_c\to J/\psi +\gamma )/J/\psi$ in $p\mathrm{C}$, $p\mathrm{Ti}$, and $p\mathrm{W}$ interactions at $920\mathrm{GeV}/c$ ($\sqrt{s}=41.6\mathrm{GeV}$) in the Feynman-x range $-0.35<x_F^{J/\psi }<0.15$ is presented. Both ${\mu }^{+}{\mu }^{-}$ and $e^{+}{e}^{-}$ $J/\psi$ decay channels are observed with an overall statistics of about 15 000 ${\chi }_c$ events, which is by far the largest available sample in pA collisions. The result is $R_{{\chi }_c}=0.188\pm {0.013}_{\mathrm{st}}{\genfrac{}{}{0ex}{}{+0.024}{-0.022}}_{\mathrm{sys}}$ averaged over the different materials, when no $J/\psi$ and ${\chi }_c$ polarizations are considered. The ${\chi }_{c1}$ to ${\chi }_{c2}$ production ratio $R_{12}=R_{{\chi }_{c}1}/R_{{\chi }_{c}2}$ is measured to be $1.02\pm 0.40$, leading to a cross section ratio $\frac{\sigma ({\chi }_{c1})}{\sigma ({\chi }_{c2})}=0.57\pm 0.23$. The dependence of $R_{{\chi }_c}$ on the Feynman-x of the $J/\psi$, $x_F^{J/\psi }$, and its transverse momentum, $p_T^{J/\psi }$, is studied, as well as its dependence on the atomic number, A, of the target. For the first time, an extensive study of possible biases on $R_{{\chi }_c}$ and $R_{12}$ due to the dependence of acceptance on the polarization states of $J/\psi$ and ${\chi }_c$ is performed. By varying the polarization parameter, ${\lambda }_{\mathrm{obs}}$, of all produced $J/\psi$’s by two sigma around the value measured by HERA-B, and considering the maximum variation due to the possible ${\chi }_{c1}$ and ${\chi }_{c2}$ polarizations, it is shown that $R_{{\chi }_c}$ could change by a factor between 1.02 and 1.21 and $R_{12}$ by a factor between 0.89 and 1.16.

We construct an action for an unstable M3-brane in M theory. We argue that, in order to find M3-brane action that upon direct dimensional reduction leads to non-Bogomol’nyi-Prasad-Sommerfield D3-brane action in type IIA theory, we have to presume that the background possesses Killing isometry and that this isometry has to be gauged on the world volume of the M3-brane. Then we construct a singular tachyon kink on the world volume of the M3-brane, and we show that the dynamics of the resulting topological defect is governed by an action that upon direct dimensional reduction leads to a D2-brane in type IIA theory and that is equivalent to standard M2-brane action in a flat background.

We discuss a class of exact solutions of a three-parameter nonminimally extended Einstein-Maxwell model, which are attributed to nonminimal magnetic monopoles of the Dirac type. We focus on the investigation of the gravitational field of Dirac monopoles for those models, for which the singularity at the central point is hidden inside of an event horizon independently on the mass and charge of the object. We obtain the relationships between the nonminimal coupling constants, for which this requirement is satisfied. As explicit examples, we consider in detail two one-parameter models: first, the nonminimally extended Reissner-Nordström model (for the magnetically charged monopole) and, second, the Drummond-Hathrell model.

We investigate the change in the decay rate of a muon caused by embedding it in the field of a laser. A previous paper found that the change could be large, as much as an order of magnitude. We find the more intuitive result that the change is small and give analytic expressions for the small corrections.

A family of diffeomorphism-invariant Seiberg-Witten deformations of gravity is constructed. In a first step Seiberg-Witten maps for an $SO(1,3)$ gauge symmetry are obtained for constant deformation parameters. This includes maps for the vierbein, the spin connection, and the Einstein-Hilbert Lagrangian. In a second step the vierbein postulate is imposed in normal coordinates and the deformation parameters are identified with the components ${\theta }^{\mu \nu }(x)$ of a covariantly constant bivector. This procedure gives for the classical action a power series in the bivector components which by construction is diffeomorphism invariant. Explicit contributions up to second order are obtained. For completeness a cosmological constant term is included in the analysis. Covariant constancy of ${\theta }^{\mu \nu }(x)$, together with the field equations, imply that, up to second order, only four-dimensional metrics which are direct sums of two two-dimensional metrics are admissible, the two-dimensional curvatures being expressed in terms of ${\theta }^{\mu \nu }$. These four-dimensional metrics can be viewed as a family of deformed emergent gravities.

We consider properties of near-critical solutions describing a test static axisymmetric $D$-dimensional brane interacting with a bulk $N$-dimensional black hole $(N>D)$. We focus our attention on the effects connected with curvature corrections to the brane action. Namely, we demonstrate that the second order phase transition in such a system is modified and becomes first order. We discuss possible consequences of these results for merger transitions between caged black holes and black strings.

If a field theory contains gauged, non-Abelian, bifundamental fields, i.e. fields that are charged under two separate non-Abelian gauge groups, the transition from a deconfined phase to a hadronic phase may be frustrated. Similar frustration may occur in non-Abelian gauge models containing matter only in higher dimensional representations, e.g. models with pure glue, or if ordinary quarks are confined by two flux tubes, as implied in the triangular configuration of baryons within QCD. In a cosmological setting, such models can lead to the formation of a web of confining electric flux tubes that can potentially have observational signatures.

Based on previous studies on computing coefficients of the electroweak chiral Lagrangian from C. T. Hill’s schematic topcolor-assisted technicolor model, we generalize the calculation to K. Lane’s prototype natural topcolor-assisted technicolor model. We find that typical features of the model are qualitatively similar to those of Hill’s, but Lane’s model prefers a smaller technicolor group and the $Z^{\prime }$ mass must be smaller than 400 GeV. Furthermore, the $S$ parameter is around the order of $+1$, mainly due to the existence of three doublets of techniquarks. We obtain the values for all coefficients of the electroweak chiral Lagrangian up to the order $p^4$. Apart from large negative four-fermion coupling values, the extended technicolor impacts on the electroweak chiral Lagrangian coefficients are small, since the techniquark self energy, which determines these coefficients, in general receives almost no influence from the extended technicolor induced four-fermion interactions except for its large momentum tail.

In this work we calculate the effects of the electroweak flavor changing neutral currents dimension six effective operators on single-top production at the LHC. These results are then combined with previous ones we have obtained for the strong sector. This allow us, for the first time, to perform a combined analysis of flavor changing neutral currents in top production with all contributing dimension six operators. Finally, we study the feasibility of their observation and characterization both at the Tevatron and at the LHC.

We extend the private Higgs scenario to account for charged lepton and neutrino masses by introducing a private Higgs field for each lepton family. We analyze a model in which neutrino Majorana masses are radiatively induced. Contrary to previous models, the neutrino mass scale $\sim {10}^{-2}\mathrm{eV}$ is naturally obtained without excessive fine-tuning. The model requires the introduction of $SU(2)$ singlet scalar fields, two charged and one neutral, $h^{+}$, $k^{++}$, and $\phi$. We discuss a possible realization giving a normal neutrino mass hierarchy. Our model fits data and predicts a nonzero $V_{e3}$.