We show that there exist uncanceled soft divergences in the $k_T$ factorization for nonfactorizable amplitudes of two-body nonleptonic $B$ meson decays, similar to those identified in hadron hadroproduction. These divergences can be grouped into a soft factor using the eikonal approximation, which is then treated as an additional nonperturbative input in the perturbative QCD formalism. Viewing the special role of the pion as a $q\overline{q}$ bound state and as a pseudo Nambu-Goldstone boson, we postulate that the soft effect associated with it is significant. This soft factor enhances the nonfactorizable color-suppressed tree amplitudes, such that the branching ratios $B({\pi }^0{\pi }^0)$ and $B({\pi }^0{\rho }^0)$ are increased under the constraint of the $B({\rho }^0{\rho }^0)$ data, the difference between the direct $CP$ asymmetries $A_{CP}({\pi }^{\mp }{K}^{\pm })$ and $A_{CP}({\pi }^0{K}^{\pm })$ is enlarged, and the mixing-induced $CP$ asymmetry $S_{{\pi }^0{K}_S}$ is reduced. Namely, the known $\pi \pi$ and $\pi K$ puzzles can be resolved simultaneously.

The first higher derivative term of the photon sector of Lorentz-violating QED, with an operator of mass dimension $d=5$, is radiatively induced from the fermion sector, which contains a derivative term with the dimensionless coefficient $g^{\lambda \mu \nu }$. The calculation is performed perturbatively in the coefficient for Lorentz violation, and, due to the fact that the contributions are quadratically divergent, we adopt dimensional regularization.

We investigate spectral properties of a fermion coupled with a massive gauge boson with a mass $m$ at finite temperature ($T$) in the perturbation theory. The massive gauge boson is introduced as a $U(1)$ gauge boson in the Stueckelberg formalism with a gauge parameter $\alpha$. We find that the fermion spectral function has a three-peak structure for $T\sim m$ irrespective of the choice of the gauge parameter, while it tends to have one faint peak at the origin and two peaks corresponding to the normal fermion and antiplasmino excitations familiar in QED in the hard thermal loop approximation for $T\gg m$. We show that our formalism successfully describe the fermion spectral function in the whole $T$ region with the correct high-$T$ limit except for the faint peak at the origin, although some care is needed for choice of the gauge parameter for $T\gg m$. We clarify that for $T\sim m$, the fermion pole is almost independent of the gauge parameter in the one-loop order, while for $T\gg m$, the one-loop analysis is valid only for $\alpha \ll 1/g$ where $g$ is the fermion-boson coupling constant, implying that the one-loop analysis cannot be valid for large gauge parameters as in the unitary gauge.

We obtain, by dimensional reduction, a ($1+1$) supersymmetric system introduced in the description of ultracold quantum gases. The correct supercharges are identified and their algebra is constructed. Finally, novel solitonic equations emerge and their solution is constructed for the bosonic case.

We investigate using plane-fronted gravitational wave space-times as model systems to study loop quantization techniques and dispersion relations. In this classical analysis we start with planar symmetric space-times in the real connection formulation. We reduce via Dirac constraint analysis to a final form with one canonical pair and one constraint, equivalent to the metric and Einstein equations of plane-fronted-with-parallel-rays waves. Because of the symmetries and use of special coordinates, general covariance is broken. However, this allows us to simply express the constraints of the consistent system. A recursive construction of Dirac brackets results in nonlocal brackets, analogous to those of self-dual fields, for the triad variables. Not surprisingly, this classical analysis produces no evidence for dispersion, i.e. a variable propagation speed of gravitational plane-fronted-with-parallel-rays waves.

The frequency of any gravitational-wave signal received from a spinning neutron star will appear Doppler-shifted by the Earth’s rotation and orbital motion. This frequency shift must be compensated to recover the signal energy as a spectral monochromatic peak with a high signal-to-noise ratio. Generally the correction depends on the source’s position in the sky, spin, and spin-down rate. Here we propose a method of applying a single correction to the data which is valid for all the emission frequencies at a fixed position in the sky and for a given spin-down rate. We advance or retard the antenna proper time by removing (or repeating) single samples of the digitized output signal to keep the effective receiver and source clocks in accurate synchronization. The method, which requires just a few lines of code and little computational effort, appears to be very effective for “semitargeted” searches, where the source direction is known but the emission frequency is not.

We consider the absorption problem for a massless scalar field propagating in static and spherically symmetric black holes of arbitrary dimension endowed with a photon sphere. For this wide class of black holes, we show that the fluctuations of the high-energy absorption cross section are totally and very simply described from the properties (dispersion relation and damping) of the waves trapped near the photon sphere and therefore, in the eikonal regime, from the characteristics (orbital period and Lyapunov exponent) of the null unstable geodesics lying on the photon sphere. This is achieved by using Regge pole techniques. They permit us to make an elegant and powerful resummation of the absorption cross section and to extract then all the physical information encoded in the sum over the partial wave contributions. Our analysis induces moreover some consequences concerning Hawking radiation which we briefly report.

We present a new solution to the cosmological constant (CC) and coincidence problems in which the observed value of the CC, $\Lambda$, is linked to other observable properties of the Universe. This is achieved by promoting the CC from a parameter that must be specified, to a field that can take many possible values. The observed value of $\Lambda \approx (9.3\mathrm{Gyrs}{)}^{-2}$ [$\approx {10}^{-120}$ in Planck units] is determined by a new constraint equation which follows from the application of a causally restricted variation principle. When applied to our visible Universe, the model makes a testable prediction for the dimensionless spatial curvature of ${\Omega }_{\mathrm{k}0}=-0.0056({\zeta }_{\mathrm{b}}/0.5)$, where ${\zeta }_{\mathrm{b}}\sim 1/2$ is a QCD parameter. Requiring that a classical history exist, our model determines the probability of observing a given $\Lambda$. The observed CC value, which we successfully predict, is typical within our model even before the effects of anthropic selection are included. When anthropic selection effects are accounted for, we find that the observed coincidence between $t_{\Lambda }={\Lambda }^{-1/2}$ and the age of the Universe, $t_{\mathrm{U}}$, is a typical occurrence in our model. In contrast to multiverse explanations of the CC problems, our solution is independent of the choice of a prior weighting of different $\Lambda$ values and does not rely on anthropic selection effects. Our model includes no unnatural small parameters and does not require the introduction of new dynamical scalar fields or modifications to general relativity, and it can be tested by astronomical observations in the near future.

The annual modulation in the rate of weakly interacting massive particle (WIMP) recoils observed by the DAMA Collaboration at high significance is often analyzed in the context of an isothermal Maxwell-Boltzmann velocity distribution. While this is the simplest model, there is a need to consider other well motivated theories of halo formation. In this paper, we study a different halo model, that of self-similar infall which is characterized by the presence of a number of cold streams and caustics, not seen in simulations. It is shown that the self-similar infall model is consistent with the DAMA result both in amplitude and in phase, for WIMP masses exceeding $\approx 250\mathrm{GeV}$ at the 99.7% confidence level. Adding a small thermal component makes the parameter space near $m_{\chi }=12\mathrm{GeV}$ consistent with the self-similar model. The minimum ${\chi }^2$ per degree of freedom is found to be 0.92(1.03) with(without) channeling taken into account, indicating an acceptable fit. For WIMP masses much greater than the mass of the target nucleus, the recoil rate depends only on the ratio ${\sigma }_{\mathrm{p}}/m_{\chi }$ which is found to be $\approx 0.06$ femtobarn/TeV. However, as in the case of the isothermal halo, the allowed parameter space is inconsistent with the null result obtained by the CDMS and XENON experiments for spin-independent elastic scattering. Future experiments with directional sensitivity and mass bounds from accelerator experiments will help to distinguish between different halo models and/or constrain the contribution from cold flows.

We compute maps of CMB temperature fluctuations seeded by cosmic strings using high resolution simulations of cosmic strings in a Friedmann-Robertson-Walker universe. We create full-sky, 18° and 3° CMB maps, including the relevant string contribution at each resolution from before recombination to today. We extract the angular power spectrum from these maps, demonstrating the importance of recombination effects. We briefly discuss the probability density function of the pixel temperatures, their skewness, and kurtosis.

Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a $\Gamma$-law equation of state with $\Gamma =4/3$. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number $m=1$ is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the $m=1$ mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.

We study renormalization group invariant (RGI) quantities in the minimal supersymmetric standard model and show that they are a powerful and simple instrument for testing high-scale models of supersymmetry (SUSY) breaking. For illustration, we analyze the frameworks of minimal and general gauge-mediated (MGM and GGM) SUSY breaking, with additional arbitrary soft Higgs mass parameters at the messenger scale. We show that if a gaugino and two first generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM sum rules that yield accurate predictions for the other gaugino and first generation soft masses. RGIs can also be used to reconstruct the fundamental MGM parameters (including the messenger scale), calculate the hypercharge $D$-term, and find relationships among the third generation and Higgs soft masses. We then study the extent to which measurements of the full first generation spectrum at the LHC may distinguish different SUSY-breaking scenarios. In the case of the MGM model, although most deviations violate the sum rules by more than estimated experimental errors, we find a one-parameter family of GGM models that satisfy the constraints and produce the same first generation spectrum. The GGM-MGM degeneracy is lifted by differences in the third generation masses and the messenger scales.

We unveil the general features of the phase diagram for any gauge theory with fermions transforming according to distinct representations of the underlying gauge group, at the four-loop order. We classify and analyze the zeros of the perturbative beta function and discover the existence of a rich phase diagram. The anomalous dimension of the fermion masses, at the infrared stable fixed point, are presented. We show that the infrared fixed point, and associated anomalous dimension, are well described by the all-orders beta function for any theory. We also argue the possible existence, to all orders, of a nontrivial ultraviolet fixed point for gauge theories at large number of flavors.

We examine the possibility that a new strong interaction is accessible to the Tevatron and the LHC. In an effective theory approach, we consider a scenario with a new color-octet interaction with strong couplings to the top quark, as well as the presence of a strongly coupled fourth generation which could be responsible for electroweak symmetry breaking. We apply several constraints, including the ones from flavor physics. We study the phenomenology of the resulting parameter space at the Tevatron, focusing on the forward-backward asymmetry in top pair production, as well as in the production of the fourth-generation quarks. We show that if the excess in the top production asymmetry is indeed the result of this new interaction, the Tevatron could see the first hints of the strongly coupled fourth-generation quarks. Finally, we show that the LHC with $\sqrt{s}=7\mathrm{TeV}$ and $1{\mathrm{fb}}^{-1}$ integrated luminosity should observe the production of fourth-generation quarks at a level at least 1 order of magnitude above the QCD prediction for the production of these states.

Pure $SU(3)$ glue theories exhibit a deconfining phase transition at a nonzero temperature, $T_c$. Using lattice measurements of the pressure, we develop a simple matrix model to describe the transition region, when $T\ge T_c$. This model, which involves three parameters, is used to compute the behavior of the ’t Hooft loop. There is a Higgs phase in this region, where off-diagonal color modes are heavy, and diagonal modes are light. Lattice measurements of the latter suggest that the transition region is narrow, extending only to about $\sim 1.2T_c$. This is in stark contrast to lattice measurements of the renormalized Polyakov loop, which indicates a much wider width. The possible implications for the differences in heavy ion collisions between the Relativistic Heavy Ion Collider and the LHC are discussed.

We present a measurement of the helicity of the $W$ boson produced in top quark decays using $t\overline{t}$ decays in the $\ell +\mathrm{\text{jets}}$ and dilepton final states selected from a sample of $5.4{\mathrm{fb}}^{-1}$ of collisions recorded using the D0 detector at the Fermilab Tevatron $p\overline{p}$ collider. We measure the fractions of longitudinal and right-handed $W$ bosons to be $f_0=0.669\pm 0.102[\pm 0.078(\mathrm{stat}.)\pm 0.065(\mathrm{syst}.)]$ and $f_{+}=0.023\pm 0.053[\pm 0.041(\mathrm{stat}.)\pm 0.034(\mathrm{syst}.)]$, respectively. This result is consistent at the 98% level with the standard model. A measurement with $f_0$ fixed to the value from the standard model yields $f_{+}=0.010\pm 0.037[\pm 0.022(\mathrm{stat}.)\pm 0.030(\mathrm{syst}.).]$.

We investigate the quantum effect on the Larmor radiation from a moving charge in an expanding universe based on the framework of the scalar quantum electrodynamics. A theoretical formula for the radiation energy is derived at the lowest order of the perturbation theory with respect to the coupling constant of the scalar quantum electrodynamics. We evaluate the radiation energy on the background universe so that the Minkowski spacetime transits to the Milne universe, in which the equation of motion for the mode function of the free complex scalar field can be exactly solved in an analytic way. Then, the result is compared with the WKB approach, in which the equation of motion of the mode function is constructed with the WKB approximation which is valid as long as the Compton wavelength is shorter than the Hubble horizon length. This demonstrates that the quantum effect on the Larmor radiation of the order $e^2\hslash$ is determined by a nonlocal integration in time depending on the background expansion. We also compare our result with a recent work by Higuchi and Walker [Phys. Rev. D 80, 105019 (2009)], which investigated the quantum correction to the Larmor radiation from a charged particle in a nonrelativistic motion in a homogeneous electric field.

Horava and Melby-Thompson recently proposed a new version of the Horava-Lifshitz theory of gravity, in which the spin-0 graviton is eliminated by introducing a Newtonian prepotential $\phi$ and a local $U(1)$ gauge field $A$. In this paper, we first derive the corresponding Hamiltonian, supermomentum constraints, the dynamical equations, and the equations for $\phi$ and $A$, in the presence of matter fields. Then, we apply the theory to cosmology and obtain the modified Friedmann equation and the conservation law of energy, in addition to the equations for $\phi$ and $A$. When the spatial curvature is different from zero, terms behaving like dark radiation and stiff-fluid exist, from which, among other possibilities, a bouncing universe can be constructed. We also study linear perturbations of the Friedmann-Robertson-Walker universe with any given spatial curvature $k$, and we derive the most general formulas for scalar perturbations. The vector and tensor perturbations are the same as those recently given by one of the present authors [A. Wang, Phys. Rev. D 82, 124063 (2010).] in the setup of Sotiriou, Visser, and Weinfurtner. Applying these formulas to the Minkowski background, we have shown explicitly that the scalar and vector perturbations of the metric indeed vanish, and the only remaining modes are the massless spin-2 gravitons.

We study the evolution of matter density perturbations in Galileon cosmology where the late-time cosmic acceleration can be realized by a field kinetic energy. We obtain full perturbation equations at linear order in the presence of five covariant Lagrangians ${\mathcal{L}}_i$ ($i=1,\cdots ,5$) satisfying the Galileon symmetry ${\partial }_{\mu }\varphi \to {\partial }_{\mu }\varphi +b_{\mu }$ in the flat space-time. The equations for a matter perturbation as well as an effective gravitational potential are derived under a quasistatic approximation on subhorizon scales. This approximation can reproduce full numerical solutions with high accuracy for the wavelengths relevant to large-scale structures. For the model parameters constrained by the background expansion history of the Universe, the growth rate of matter perturbations is larger than that in the $\Lambda$-cold dark matter model, with the growth index $\gamma$ today typically smaller than 0.4. We also find that, even on very large scales associated with the integrated-Sachs-Wolfe effect in cosmic microwave background temperature anisotropies, the effective gravitational potential exhibits a temporal growth during the transition from the matter era to the epoch of cosmic acceleration. These properties are useful to distinguish the Galileon model from the $\Lambda$-cold dark matter model in future high-precision observations.