A model is developed in which the inflaton potential experiences a sudden small change in its second derivative (the effective mass of the inflaton). An exact treatment demonstrates that the resulting density perturbation has a quasiflat power spectrum with a break in its slope (a step in $n_s$). The step in the spectral index is modulated by characteristic oscillations and results in large running of the spectral index localized over a few e-folds of scales. A field-theoretic model giving rise to such behavior of the inflationary potential is based on a fast phase transition experienced by a second scalar field weakly coupled to the inflaton. Such a transition is similar to that which terminates inflation in the hybrid inflationary scenario. This scenario suggests that the observed running of the spectral index in the WMAP data may be caused by a fast second order phase transition which occurred during inflation.

We investigate the role of nonperturbative, bubblelike inhomogeneities on the decay rate of false-vacuum states in two- and three-dimensional scalar field theories. The inhomogeneities are induced by setting up large-amplitude oscillations of the field about the false vacuum, as, for example, after a rapid quench or in certain models of cosmological inflation. We show that, for a wide range of parameters, the presence of large-amplitude bubblelike inhomogeneities greatly accelerates the decay rate, changing it from the well-known exponential suppression of homogeneous nucleation to a power-law suppression. It is argued that this fast, power-law vacuum decay—known as resonant nucleation—is promoted by the presence of long-lived oscillons among the nonperturbative fluctuations about the false vacuum. A phase diagram is obtained distinguishing three possible mechanisms for vacuum decay: homogeneous nucleation, resonant nucleation, and crossover. Possible applications are briefly discussed.

We analyze the $CP$ violation in the semileptonic $|\Delta S|=1$ $\tau$ decays in supersymmetric extensions of the standard model with $R$ parity violating term. We show that the $CP$ asymmetry of $\tau$ decay is enhanced significantly and the current experimental limits obtained by CLEO collaborations can be easily accommodated. We argue that observing $CP$ violation in semileptonic $\tau$ decay would be a clear evidence for $R$ parity violating supersymmetry extension of the standard model.

We discuss in detail the shear viscosity coefficient $\eta$ and the viscosity to entropy density ratio $\eta /s$ of a hadronic gas comprised of pions and nucleons. In particular, we study the effects of baryon chemical potential on $\eta$ and $\eta /s$. We solve the relativistic quantum Boltzmann equations with binary collisions ($\pi \pi$, $\pi N$, and $NN$) for a state slightly deviated from thermal equilibrium at temperature $T$ and baryon chemical potential $\mu$. The use of phenomenological amplitudes in the collision terms, which are constructed to reproduce experimental data, greatly helps to extend the validity region in the $T\mathrm{\text{−}}\mu$ plane. The total viscosity coefficient $\eta (T,\mu )={\eta }^{\pi }+{\eta }^N$ increases as a function of $T$ and $\mu$, indirectly reflecting energy dependences of binary cross sections. The increase in $\mu$ direction is due to enhancement of the nucleon contribution ${\eta }^N$ while the pion contribution ${\eta }^{\pi }$ diminishes with increasing $\mu$. On the other hand, due to rapid growth of entropy density, the ratio $\eta /s$ becomes a decreasing function of $T$ and $\mu$ in a wide region of the $T\mathrm{\text{−}}\mu$ plane. In the kinematical region we investigated $T<180\mathrm{MeV}$, $\mu <1\mathrm{GeV}$, the smallest value of $\eta /s$ is about 0.3. Thus, it never violates the conjectured lower bound $\eta /s=1/4\pi \sim 0.1$. The smallness of $\eta /s$ in the hadronic phase and its continuity at $T\simeq T_c$ (at least for crossover at small $\mu$) implies that the ratio will be small enough in the deconfined phase $T\gtrsim T_c$. There is a nontrivial structure at low temperature and at around normal nuclear density. We examine its possible interpretation as the liquid-gas phase transition.

We address the flavor problem by incorporating the hypothesis of universal strength of Yukawa couplings in the framework of a 5D GUT model compactified on an $S^1/(Z_2\times Z_2^{\prime })$ orbifold. We show that a quantitatively successful picture of fermion masses and mixings emerges from the interplay between the bulk suppression factors of geometric origin and the phases of the Yukawa matrices. We give an explicit example, where we obtain a good fit for both the Cabibbo-Kobayashi-Maskawa and Pontecorvo-Maki-Nakagawa-Sakata matrices.

The process $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ is observed for the first time via initial-state radiation. The cross section of $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ for center-of-mass energies between threshold and 6.0 GeV is measured using $673{\mathrm{fb}}^{-1}$ of data collected with the Belle detector on and off the ${\rm Y}(4S)$ resonance. No significant signal for $Y(4260)\to K^{+}{K}^{-}J/\psi$ is observed, and we determine $\mathcal{B}(Y(4260)\to K^{+}{K}^{-}J/\psi )\Gamma (Y(4260)\to e^{+}{e}^{-})<1.2\mathrm{eV}/c^2$ at a 90% confidence level. We also find evidence for $e^{+}{e}^{-}\to K_S^0{K}_S^{0}J/\psi$ in the same data sample.

We reconsider spherically symmetric black hole solutions in Einstein-Aether theory with the condition that this theory has identical parametrized post-Newtonian parameters as those for general relativity, which is the main difference from the previous research. In contrast with previous study, we allow superluminal propagation of a spin-0 Aether-gravity wave mode. As a result, we obtain black holes having a spin-0 “horizon” inside an event horizon. We allow a singularity at a spin-0 horizon since it is concealed by the event horizon. If we allow such a configuration, the kinetic term of the Aether field can be large enough for black holes to be significantly different from Schwarzschild black holes with respect to Arnowitt-Deser-Misner mass, innermost stable circular orbit, Hawking temperature, and so on. We also discuss whether or not the above features can be seen in more generic vector-tensor theories.

While the definition of static equilibria is not clear in a general relativistic context, in many cases of astrophysical interest a natural $3+1$ split exists which allows us to define physically meaningful spatial and temporal coordinates. We study the possibility of axisymmetric magnetohydrodynamic equilibria in this setting. The presence of a nontrivial shift velocity provides a constraint not present in the Newtonian case, while the momentum equation may be set in a Grad-Shafranov-like form with the presence of additional terms involving the space-time metric coefficients. It is found that whenever the magnetic field or the shift velocity possesses poloidal component, the existence of even local static equilibria demands that the metric parameters satisfy such strong conditions that these equilibria are extremely unlikely. Only very particular cases such as purely toroidal fields and shifts yield existence of equilibria, provided we are able to choose arbitrarily the plasma pressure and density.

We give a rigorous and mathematically well defined presentation of the covariant and gauge invariant theory of scalar perturbations of a Friedmann-Lemaître-Robertson-Walker universe for fourth order gravity, where the matter is described by a perfect fluid with a barotropic equation of state. The general perturbations equations are applied to a simple background solution of $R^n$ gravity. We obtain exact solutions of the perturbations equations for scales much bigger than the Hubble radius. These solutions have a number of interesting features. In particular, we find that for all values of $n$ there is always a growing mode for the density contrast, even if the universe undergoes an accelerated expansion. Such behavior does not occur in standard general relativity, where as soon as dark energy dominates, the density contrast experiences an unrelenting decay. This peculiarity is sufficiently novel to warrant further investigation of fourth order gravity models.

It is well known that magnification bias, the modulation of galaxy or quasar source counts by gravitational lensing, can change the observed angular correlation function. We investigate magnification-induced changes to the shape of the observed correlation function $w(\theta )$, and the angular power spectrum $C_{\ell }$, paying special attention to the matter-radiation equality peak and the baryon wiggles. Lensing effectively mixes the correlation function of the source galaxies with that of the matter correlation at the lower redshifts of the lenses distorting the observed correlation function. We quantify how the lensing corrections depend on the width of the selection function, the galaxy bias $b$, and the number count slope $s$. The lensing correction increases with redshift and larger corrections are present for sources with steep number count slopes and/or broad redshift distributions. The most drastic changes to $C_{\ell }$ occur for measurements at high redshifts ($z\gtrsim 1.5$) and low multipole moment ($\ell \lesssim 100$). For the source distributions we consider, magnification bias can shift the location of the matter-radiation equality scale by 1%–6% at $z\sim 1.5$ and by $z\sim 3.5$ the shift can be as large as 30%. The baryon bump in ${\theta }^{2}w(\theta )$ is shifted by $\lesssim 1\%$ and the width is typically increased by $\sim 10\%$. Shifts of $\gtrsim 0.5\%$ and broadening $\gtrsim 20\%$ occur only for very broad selection functions and/or galaxies with $(5s-2)/b\gtrsim 2$. However, near the baryon bump the magnification correction is not constant but is a gently varying function which depends on the source population. Depending on how the $w(\theta )$ data is fitted, this correction may need to be accounted for when using the baryon acoustic scale for precision cosmology.

We analyze the trajectories for multifield Dirac-Born-Infeld inflation, which can arise in brane inflation models, and show that the trajectories are the same as in typical slow roll inflation. We calculate the power spectrum and find that the higher derivative terms of the Dirac-Born-Infeld action lead to a suppression of the contribution from the isocurvature perturbations. We also calculate the bispectrum generated by the isocurvature perturbation, and find that it leads to distinctive features.

We calculate the two-loop QCD corrections to paracharmonium decays ${\eta }_c\to \gamma \gamma$ and ${\eta }_c\to gg$ involving light-by-light scattering diagrams with light quark loops. Artificial large mass expansion and convergence improvement techniques are used to evaluate these corrections. The obtained corrections to the decays ${\eta }_c\to \gamma \gamma$ and ${\eta }_c\to gg$ account for $-1.25\%$ and $-0.73\%$ of the leading order contribution, respectively.

Recent PVLAS data put stringent constraints on the measurement of birefringence and dichroism of electromagnetic waves travelling in the constant and homogeneous magnetic field. There have been theoretical predictions in favor of such phenomena when appropriate axion-electromagnetic coupling is assumed. Origin of such a coupling can be traced in a low energy string action from the requirement of quantum consistency. The resulting couplings in such models are an artifact of the compactification of the extra dimensions present inevitably in a string scenario. The moduli parameters which encode the compact manifold therefore play a crucial role in determining the axion-photon coupling. In this work we examine the possible bounds on the value of compact modulus that emerge from the experimental limits on the coupling obtained from the PVLAS data. In particular we focus into the Randall-Sundrum (RS) type of warped geometry model whose modulus parameter is already restricted from the requirement of the resolution of the gauge hierarchy problem in connection with the mass of the Higgs. We explore the bound on the modulus for a wide range of the axion mass for both the birefringence and the dichroism data in PVLAS. We show that the proposed value of the modulus in the RS scenario can only be accommodated for axion mass $\gtrsim 0.3\mathrm{eV}$.

We examine very general four-point interactions arising from new physics and contributing to the Higgs production process $e^{+}{e}^{-}\to HZ$. We write all possible forms for these interactions consistent with Lorentz invariance. We allow the possibility of $CP$ violation. Contributions to the process from anomalous $ZZH$ and $\gamma ZH$ interactions studied earlier arise as a special case of our four-point amplitude. We consider the decay of $Z$ into a charged-lepton pair and obtain expressions for angular distributions of charged leptons arising from the interference of the four-point contribution with the standard-model contribution. We take into account possible longitudinal or transverse beam polarization likely to be available at a linear collider. We examine several correlations which can be used to study the various form factors present in the $e^{+}{e}^{-}HZ$ contact interactions. We also obtain the sensitivity of these correlations in constraining the new-physics interactions at a linear collider operating at a center-of-mass energy of 500 GeV with longitudinal or transverse polarization.

We consider a scenario where a supersymmetric model has multiple dark matter particles. Adding a $U(1{)}^{\prime }$ gauge symmetry is a well-motivated extension of the minimal supersymmetric standard model (MSSM). It can cure the problems of the MSSM such as the $\mu$ problem or the proton decay problem with high-dimensional lepton number and baryon number violating operators which $R$ parity allows. An extra parity ($U$ parity) may arise as a residual discrete symmetry after $U(1{)}^{\prime }$ gauge symmetry is spontaneously broken. The lightest $U$-parity particle (LUP) is stable under the new parity becoming a new dark matter candidate. Up to three massive particles can be stable in the presence of the $R$ parity and the $U$ parity. We numerically illustrate that multiple stable particles in our model can satisfy both constraints from the relic density and the direct detection, thus providing a specific scenario where a supersymmetric model has well-motivated multiple dark matters consistent with experimental constraints. The scenario provides new possibilities in the present and upcoming dark matter searches in the direct detection and collider experiments.

We consider transitions from the resonance $X(3872)$ to the ${\chi }_{cJ}$ states of charmonium with emission of one or two pions as a means of studying the structure of the $X$ resonance. We find that the relative rates for these transitions to the final states with different $J$ significantly depend on whether the initial state is a pure charmonium state or a four-quark/molecular state.

We study how to assign the recently observed $D_{sJ}(2700)$ meson to an appropriate level of the $c\overline{s}$ spectrum by the analysis of its decay modes in final states comprising a light pseudoscalar meson. We use an effective Lagrangian approach with heavy quark and chiral symmetries, obtaining that the measurement of the $D^{*}K$ decay width would allow one to distinguish between two possible assignments.

We study the action of space-time symmetries on quantum fields in the presence of small departures from locality determined by dynamical gravity. It is shown that, under such relaxation of locality the symmetries of the theory cannot be described within the usual framework of Lie algebras but rather in terms of noncocommutative Hopf algebras or “quantum groups.” Similar “quantizations” of space-time symmetries are expected to emerge in the low-energy limit of certain quantum gravity models and have been used to describe the symmetries of various noncommutative space-times. Our result provides an intuitive characterization of the mechanism that could lead to the emergence of deformed coproducts in models of quantum relativistic symmetries.

We construct a modification of the standard model which stabilizes the Higgs mass against quadratically divergent radiative corrections, using ideas originally discussed by Lee and Wick in the context of a finite theory of quantum electrodynamics. The Lagrangian includes new higher derivative operators. We show that the higher derivative terms can be eliminated by introducing a set of auxiliary fields; this allows for convenient computation and makes the physical interpretation more transparent. The theory is thought to be unitary, but nevertheless, it does not satisfy the usual analyticity conditions.

Results for four-, five-, and six-parton tree amplitudes for massive quark-antiquark scattering with gluons are calculated using the recursion relations of Britto, Cachazo, Feng, and Witten. The required diagrams are generated using shifts of the momenta of a pair of massless legs to complex values. Checks verifying the calculations are described, and a simple formula for the shifted spinors of an internal gluon is presented.