In the framework of the perturbative QCD approach, we study the charmless pure weak annihilation $B_c^{-}\to K^{-}{K}^0$ decay and find that the branching ratio $\mathcal{B}\mathcal{R}(B_c\to KK)\sim \mathcal{O}({10}^{-7})$. This prediction is so tiny that the $B_c\to KK$ decay might be unmeasurable at the Large Hadron Collider.

The isotriplet ${\Sigma }_c(2800)$ baryon with possible quantum numbers $J^P={\frac{1}{2}}^{\pm }$ or ${\frac{3}{2}}^{\pm }$ is considered as a hadronic molecule composed of a nucleon and a $D$ meson. We determine the strong two-body decay widths ${\Sigma }_c\to {\Lambda }_c\pi$ which are shown to be consistent with current data for the $J^P={\frac{1}{2}}^{+}$ and $J^P={\frac{3}{2}}^{-}$ assignments.

We make an estimate of the likelihood function for the Higgs vacuum expectation value (vev) by imposing anthropic constraints on the existence of atoms while allowing the other parameters of the standard model to also be variable. We argue that the most important extra ingredients are the Yukawa couplings, and for the intrinsic distribution of Yukawa couplings we use the scale-invariant distribution which is favored phenomenologically. The result is successful phenomenologically, favoring values close to the observed vev. We also discuss modifications that can change these conclusions. Our work supports the hypothesis that the anthropic constraints could be the origin of the small Higgs vev.

In the presence of large extra dimensions, the fundamental scale could be as low as a few TeV. This yields leptogenesis and seesaw at a TeV scale. Phenomenologically, two TeV-scale Majorana fermions with a small mass split can realize a resonant leptogenesis, whereas a TeV-scale Higgs triplet with a small trilinear coupling to the standard model Higgs doublet can give a verifiable seesaw. We propose an interesting scenario where the small parameters for the resonant leptogenesis and the type-II seesaw can be simultaneously generated by the propagation of lepton number violation from distant branes to our world.

We consider the electron-positron pair creation by a photon in an external constant electric field. The presented treatment is based on a purely quasiclassical calculation of the imaginary part of the on-shell photon polarization operator. By using this approach we find the pair production rate for photons with polarization parallel as well as orthogonal to the external electric field in the leading order in the parameter $eE/m^2$, which has been recently found by other methods. For the orthogonal polarization we also find a new contribution to the rate, which is leading in the ratio of the photon energy to the electron mass $\omega /m$. We also reproduce by a purely geometrical calculation the exponential factor in the probability of the stimulated pair creation at arbitrary energy of the photon.

The master formula approach to chiral symmetry breaking proposed by Yamagishi and Zahed is extended to the ${\mathrm{U}}_R(3)\times {\mathrm{U}}_L(3)$ group in which effects of the ${\mathrm{U}}_A(1)$ anomaly and flavor symmetry breaking, $m_u\ne m_d\ne m_s$, are taken into account. New identities for the gluon topological susceptibility and ${\pi }^0$, $\eta$, ${\eta }^{\prime }\to {\gamma }^{(*)}{\gamma }^{(*)}$ decays are derived, which embody the consequences of broken chiral symmetry in QCD without relying on any unphysical limits.

The concept of chirality is extended to the minimal supersymmetric standard model and the $\mu$-term is forbidden by a gauged $U(1{)}^{\prime }$ symmetry. $R$-parity automatically emerges after symmetry breaking, suppressing proton decay and protecting the lightest supersymmetric particle. Exotics charged under the standard model pose a challenge to traditional $SU(5)$ unification, but unification is still implemented in deconstructed grand unified theories. Because of the multitude of additional states to the minimal supersymmetric standard model, the $Z^{\prime }$ has a large width, and the standard model background, neglected in previous theoretical studies, becomes important for $Z^{\prime }$ discovery. As a result, the CERN LHC reach is reduced from 3.2 TeV, for a $Z^{\prime }$ with standard model decays, to 1.5 TeV, when additional decay channels are included. This model also predicts possibly long-lived colored and electroweak exotics.

The recently developed “data set diagonalization” method is applied to measure compatibility of the data sets that are used to determine parton distribution functions. Discrepancies among the experiments are found to be somewhat larger than is predicted by propagating the published experimental errors according to Gaussian statistics. The results support a tolerance criterion of $\Delta {\chi }^2\approx 10$ to estimate the 90% confidence range for parton distribution function uncertainties. No basis is found in the data sets for the larger $\Delta {\chi }^2$ values that are in current use, though it may be necessary to retain those larger values until improved methods can be developed to take account of systematic errors in applying the theory, including the effect of parametrization dependence. The data set diagonalization method also measures how much influence each experiment has on the global fit and identifies experiments that show significant tension with respect to the others. The method is used to explore the contribution from muon scattering experiments, which are found to exhibit the largest discrepancies in the current fit.

We derive a factorization theorem that describes an energetic hadron $h$ fragmenting from a jet produced by a parton $i$, where the jet invariant mass is measured. The analysis yields a “fragmenting jet function” ${\mathcal{G}}_i^h(s,z)$ that depends on the jet invariant mass $s$, and on the energy fraction $z$ of the fragmentation hadron. We show that ${\mathcal{G}}_i^h$ can be computed in terms of perturbatively calculable coefficients, ${\mathcal{J}}_{ij}(s,z/x)$, integrated against standard nonperturbative fragmentation functions, $D_j^h(x)$. We also show that $\sum _h\int dz{\mathcal{G}}_i^h(s,z)$ is given by the standard inclusive jet function $J_i(s)$ which is perturbatively calculable in QCD. We use soft collinear effective theory and for simplicity carry out our derivation for a process with a single jet, $\overline{B}\to Xh\ell \overline{\nu }$, with invariant mass $m_{Xh}^2\gg {\Lambda }_{\mathrm{QCD}}^2$. Our analysis yields a simple replacement rule that allows any factorization theorem depending on an inclusive jet function $J_i$ to be converted to a semi-inclusive process with a fragmenting hadron $h$. We apply this rule to derive factorization theorems for $\overline{B}\to XK\gamma$ which is the fragmentation to a Kaon in $b\to s\gamma$, and for $e^{+}{e}^{-}\to (\mathrm{\text{dijets}})+h$ with measured hemisphere dijet invariant masses.

We consider the effects of spacetime curvature and brane thickness on the localization of gauge fields on a brane via kinetic terms induced by localized fermions. We find that in a warped geometry with an infinitely thin brane, both the infrared and the ultraviolet behavior of the electromagnetic propagator are affected, providing a more stringent bound on the brane’s tension than that coming from the requirement of four-dimensional gravity on the brane. On the other hand, for a thick wall in a flat spacetime, where the fermions are localized by means of a Yukawa coupling, we find that four-dimensional electromagnetism is recovered in a region bounded from above by the same critical distance appearing in the thin case, but also from below by a new scale related to the brane’s thickness and the electromagnetic couplings. This imposes very stringent bounds on the brane’s thickness which seem to invalidate the localization mechanism for this case.

We retrieve the non-BPS extremal black hole superpotential of $\mathcal{N}=8$, $d=4$ supergravity by using the Maurer-Cartan equations of the symmetric space $\frac{E_{7(7)}}{SU(8)}$. This superpotential was recently obtained with different 3- and 4-dimensional techniques. The present derivation is independent on the reduction to $d=3$.

We study the effect of color superconductivity and neutrino trapping on the deconfinement transition of hadronic matter into quark matter in a protoneutron star. To describe the strongly interacting matter a two-phase picture is adopted. For the hadronic phase we use different parametrizations of a nonlinear Walecka model which includes the whole baryon octet. For the quark-matter phase we use an $SU(3{)}_f$ Nambu–Jona-Lasinio effective model which includes color superconductivity. We impose color and flavor conservation during the transition in such a way that just deconfined quark matter is transitorily out of equilibrium with respect to weak interactions. We find that deconfinement is more difficult for small neutrino content and it is easier for lower temperatures although these effects are not too large. In addition they will tend to cancel each other as the protoneutron star cools and deleptonizes, resulting a transition density that is roughly constant along the evolution of the protoneutron star. According to these results the deconfinement transition is favored after substantial cooling and contraction of the protoneutron star.

We consider composite string solutions in $\mathcal{N}=2$ SQCD with the gauge group $\mathrm{U}(N)$, the Fayet–Iliopoulos term $\xi \ne 0$ and $N$ (s)quark flavors. These bulk theories support non-Abelian strings and confined monopoles identified with kinks in the two-dimensional world-sheet theory. Similar and more complicated kinks (corresponding to composite confined monopoles) must exist in the world-sheet theories on composite strings. In a bid to detect them we analyze the Hanany–Tong (HT) model, focusing on a particular example of $N=2$. Unequal quark mass terms in the bulk theory result in the twisted masses in the $\mathcal{N}=(2,2)$ HT model. For spatially coinciding 2-strings, we find three distinct minima of potential energy, corresponding to three different 2-strings. Then we find BPS-saturated kinks interpolating between each pair of vacua. Two kinks can be called elementary. They emanate one unit of the magnetic flux and have the same mass as the conventional ’t Hooft–Polyakov monopole on the Coulomb branch of the bulk theory ($\xi =0$). The third kink represents a composite bimonopole, with twice the minimal magnetic flux. Its mass is twice the mass of the elementary confined monopole. We find instantons in the HT model, and discuss quantum effects in composite strings at strong coupling. In addition, we study the renormalization group flow in this model.

We present a numerical code for calculating the local gravitational self-force acting on a pointlike particle in a generic (bound) geodesic orbit around a Schwarzschild black hole. The calculation is carried out in the Lorenz gauge: For a given geodesic orbit, we decompose the Lorenz-gauge metric perturbation equations (sourced by the delta-function particle) into tensorial harmonics, and solve for each harmonic using numerical evolution in the time domain (in $1+1$ dimensions). The physical self-force along the orbit is then obtained via mode-sum regularization. The total self-force contains a dissipative piece as well as a conservative piece, and we describe a simple method for disentangling these two pieces in a time-domain framework. The dissipative component is responsible for the loss of orbital energy and angular momentum through gravitational radiation; as a test of our code we demonstrate that the work done by the dissipative component of the computed force is precisely balanced by the asymptotic fluxes of energy and angular momentum, which we extract independently from the wave-zone numerical solutions. The conservative piece of the self-force does not affect the time-averaged rate of energy and angular-momentum loss, but it influences the evolution of the orbital phases; this piece is calculated here for the first time in eccentric strong-field orbits. As a first concrete application of our code we recently reported the value of the shift in the location and frequency of the innermost stable circular orbit due to the conservative self-force [Phys. Rev. Lett. 102, 191101 (2009)]. Here we provide full details of this analysis, and discuss future applications.

We develop a fully covariant, well-posed $5D$ effective action for the $6D$ cascading gravity brane-world model, and use this to study cosmological solutions. We obtain this effective action through the $6D$ decoupling limit, in which an additional scalar degree mode, $\pi$, called the brane-bending mode, determines the bulk-brane gravitational interaction. The $5D$ action obtained this way inherits from the sixth dimension an extra $\pi$ self-interaction kinetic term. We compute appropriate boundary terms, to supplement the $5D$ action, and hence derive fully covariant junction conditions and the $5D$ Einstein field equations. Using these, we derive the cosmological evolution induced on a 3-brane moving in a static bulk. We study the strong- and weak-coupling regimes analytically in this static ansatz, and perform a complete numerical analysis of our solution. Although the cascading model can generate an accelerating solution in which the $\pi$ field comes to dominate at late times, the presence of a critical singularity prevents the $\pi$ field from dominating entirely. Our results open up the interesting possibility that a more general treatment of degravitation in a time-dependent bulk, or taking into account finite brane-thickness effects, may lead to an accelerating universe without a cosmological constant.

We study nonaxisymmetric oscillations of rapidly and differentially rotating relativistic stars in the Cowling approximation. Our equilibrium models are sequences of relativistic polytropes, where the differential rotation is described by the relativistic $j$-constant law. We show that a small degree of differential rotation raises the critical rotation value for which the quadrupolar f-mode becomes prone to the Chandrasekhar-Friedman-Schutz (CFS) instability, while the critical value of $T/|W|$ at the mass-shedding limit is raised even more. For stiffer equations of state these effects are even more pronounced. When increasing differential rotation further to a high degree, the neutral point of the CFS instability first reaches a local maximum and is lowered afterwards. For stars with a rather high compactness we find that for a large degree of differential rotation the absolute value of the critical $T/|W|$ is below the corresponding value for rigid rotation. We conclude that the onset of the CFS instability is eased for a small degree of differential rotation and for a large degree at least in stars with a higher compactness. Moreover, we were able to extract the eigenfrequencies and the eigenfunctions of r-modes for differentially rotating stars and our simulations show a good qualitative agreement with previous Newtonian results.

We investigate the basic theoretical issues in the quantum entanglement of particle pairs created from the vacuum in a time-dependent background field or spacetime. Similar to entropy generation from these processes which depends on the choice of physical variables and how certain information is coarse grained, entanglement dynamics hinges on the choice of measurable quantities and how the two parties are selected as well as the background dynamics of the field or spacetime. We discuss the conditions of separability of quantum states in particle creation processes and point out the differences in how the von Neumann entropy is used as a measure of entropy generation versus for entanglement dynamics. We show by an explicit construction that adoption of a different set of physical variables yields a different entanglement entropy. As an application of these theoretical considerations we show how the particle number and the quantum phase enter the entanglement dynamics in cosmological particle production.

Dark energy must cluster in order to be consistent with the equivalence principle. The background evolution can be effectively modeled by either a scalar field or by a barotropic fluid. The fluid model can be used to emulate perturbations in a scalar field model of dark energy, though this model breaks down at large scales. In this paper we study evolution of dark energy perturbations in canonical scalar field models: the classes of thawing and freezing models. The dark energy equation of state evolves differently in these classes. In freezing models, the equation of state deviates from that of a cosmological constant at early times. For thawing models, the dark energy equation of state remains near that of the cosmological constant at early times and begins to deviate from it only at late times. Since the dark energy equation of state evolves differently in these classes, the dark energy perturbations too evolve differently. In freezing models, since the equation of state deviates from that of a cosmological constant at early times, there is a significant difference in evolution of matter perturbations from those in the cosmological constant model. In comparison, matter perturbations in thawing models differ from the cosmological constant only at late times. This difference provides an additional handle to distinguish between these classes of models and this difference should manifest itself in the integrated Sachs-Wolfe effect.

Numerical simulations of dark matter collapse and structure formation show that in addition to a large halo surrounding the baryonic component of our galaxy, there also exists a significant number of subhalos that extend hundreds of kiloparsecs beyond the edge of the observable Milky Way. We find that for dark matter (DM) annihilation models, galactic subhalos can significantly modify the spectrum of electrons and positrons as measured at our galactic position. Using data from the recent Via Lactea II simulation we include the subhalo contribution of electrons and positrons as boundary source terms for simulations of high energy cosmic ray propagation with a modified version of the publicly available GALPROP code. Focusing on the DM $\mathrm{DM}\to 4e$ annihilation channel, we show that including subhalos leads to a better fit to both the Fermi and PAMELA data. The best fit gives a dark matter particle mass of 1.2 TeV, for boost factors of $B_{\mathrm{MH}}=90$ in the main halo and $B_{\mathrm{SH}}=1950-3800$ in the subhalos (depending on assumptions about the background), in contrast to the 0.85 TeV mass that gives the best fit in the main halo-only scenario. These fits suggest that at least a third of the observed electron cosmic rays from DM annihilation could come from subhalos, opening up the possibility of a relaxation of recent stringent constraints from inverse Compton gamma rays originating from the high-energy leptons.

I consider constraints on a phenomenological decaying dark matter model, in which two weakly interacting massive particle species have a small mass splitting, and in which the heavier particle decays to the lighter particle and a massless particle on cosmological time scales. The decay parameter space is parametrized by $v_{\mathrm{k}}$, the speed of the lighter particle in the center-of-mass frame of the heavier particle prior to decay, and the decay time $\tau$. Since I consider the case in which dark matter halos have formed before there has been significant decay, I focus on the effects of decay on already formed halos. I show that the $v_{\mathrm{k}}-\tau$ parameter space may be constrained by observed properties of dark matter halos. I highlight which set of observations is likely to yield the cleanest constraints on $v_{\mathrm{k}}-\tau$ parameter space, and calculate the constraints in those cases in which the effect of decay on the observables can be calculated without $N$-body simulations of decaying dark matter. I show that for $v_{\mathrm{k}}\gtrsim 5\times {10}^3\mathrm{km}{\mathrm{s}}^{-1}$, the $z=0$ galaxy cluster mass function and halo mass-concentration relation constrain $\tau \gtrsim 40\mathrm{Gyr}$, and that precise constraints on $\tau$ for smaller $v_{\mathrm{k}}$ will require $N$-body simulations.