We investigate the two-body weak nonleptonic decays of ${\Lambda }_b^0$, ${\Xi }_b^0$, and ${\Xi }_b^{-}$ into the octet baryons ($J^P=1/2^{+}$) and axial-vector mesons ($J^P=1^{+}$) employing the factorization scheme and obtain their branching ratios and asymmetry parameters.

Experiment E949 at Brookhaven National Laboratory has observed three new events consistent with the decay $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ in the pion momentum region $140<P_{\pi }<199\mathrm{MeV}/c$ in an exposure of $1.71\times {10}^{12}$ stopped kaons with an estimated total background of $0.93\pm 0.17(\mathrm{stat}{)}_{-0.24}^{+0.32}(\mathrm{syst})$ events. This brings the total number of observed $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ events to seven. Combining this observation with previous results, assuming the pion spectrum predicted by the standard model, results in a branching ratio of $\mathcal{B}(K^{+}\to {\pi }^{+}\nu \overline{\nu })=({1.73}_{-1.05}^{+1.15})\times {10}^{-10}$. An interpretation of the results for alternative models of the decay $K^{+}\to {\pi }^{+}+nothing$ is also presented.

A relatively simple approach to noncommutative gravity utilizes the gauge theory formulation of general relativity and involves replacing the Lorentz gauge group by a larger group. This results in additional field degrees of freedom which either must be constrained to vanish in a nontrivial way or require physical interpretation. With the latter in mind, we examine the coupling of the additional fields to point particles. Nonstandard particle degrees of freedom should be introduced in order to write down the most general coupling. The example we study is the $GL(2,C)$ central extension of gravity given by Chamseddine, which contains two $U(1)$ gauge fields and a complex vierbein matrix, along with the usual spin connections. For the general coupling one should then attach two $U(1)$ charges and a complex momentum vector to the particle, along with the spin. The momenta span orbits in a four-dimensional complex vector space and are classified by $GL(2,C)$ invariants and by their little groups. In addition to orbits associated with standard massive and massless particles, a number of novel orbits can be identified. We write down a general action principle for particles associated with any nontrivial orbit and show that it leads to corrections to geodesic motion. We also examine the classical and quantum theory of the particle in flat space-time.

We analyze the theory and phenomenology of anomalous global chiral symmetries in the presence of an extra dimension. We propose a simple extension of the standard model in 5D whose signatures closely resemble those of supersymmetry with gauge mediation, and we suggest a novel scalar dark matter candidate.

We find nontrivial, time-dependent solutions of the (anti) self-dual Yang-Mills equations in the four-dimensional Euclidean anti-de Sitter space. In contrast to the Euclidean flat space, the action depends on the moduli parameters and the charge can take any noninteger value.

Primordial black holes (PBHs) can form in the early Universe via the collapse of large density perturbations. There are tight constraints on the abundance of PBHs formed due to their gravitational effects and the consequences of their evaporation. These abundance constraints can be used to constrain the primordial power spectrum, and hence models of inflation, on scales far smaller than those probed by cosmological observations. We compile, and where relevant update, the constraints on the abundance of PBHs before calculating the constraints on the curvature perturbation, taking into account the growth of density perturbations prior to horizon entry. We consider two simple parametrizations of the curvature perturbation spectrum on the scale of interest: constant and power-law. The constraints from PBHs on the amplitude of the power spectrum are typically in the range ${10}^{-2}–{10}^{-1}$ with some scale dependence.

We investigate the oscillations of slowly rotating superfluid stars, taking into account the vortex-mediated mutual friction force that is expected to be the main damping mechanism in mature neutron star cores. Working to linear order in the rotation of the star, we consider both the fundamental $f$-modes and the inertial $r$-modes. In the case of the (polar) $f$-modes, we work out an analytic approximation of the mode which allows us to write down a closed expression for the mutual friction damping time scale. The analytic result is in good agreement with previous numerical results obtained using an energy integral argument. We extend previous work by considering the full range of permissible values for the vortex drag, e.g. the friction between each individual vortex and the electron fluid. This leads to the first ever results for the $f$-mode in the strong drag regime. Our estimates provide useful insight into the dependence on, and relevance of, various equation of state parameters. In the case of the (axial) $r$-modes, we confirm the existence of two classes of modes. However, we demonstrate that only one of these sets remains purely axial in more realistic neutron star models. Our analysis lays the foundation for companion studies of the mutual friction damping of the $r$-modes at second order in the slow-rotation approximation, the first time evolutions for superfluid neutron star perturbations and also the first detailed attempt at studying the dynamics of superfluid neutron stars with both a relative rotation between the components and mutual friction.

Thermal noise of a mirror is one of the limiting noise sources in the high-precision measurement such as gravitational-wave detection, and the modeling of thermal noise has been developed and refined over a decade. In this paper, we present a derivation of coating thermal noise of a finite-size cylindrical mirror based on the fluctuation-dissipation theorem. The result agrees to a previous result with an infinite-size mirror in the limit of large thickness, and also agrees to an independent result based on the modal-expansion method with a thin-mirror approximation. Our study will play an important role not only to accurately estimate the thermal-noise level of gravitational-wave detectors but also to help in analyzing thermal noise in quantum-measurement experiments with lighter mirrors.

We discuss the coupling of heavy moduli fields to light fields when the dynamics of the latter, absent such couplings, yields metastable vacua. We show that the survival of the vacuum structure of the local model depends nontrivially on the cross couplings of the two sectors. In particular we find that for local models (such as those realized by D-branes in type II string theories) with metastable vacua breaking supersymmetry via $F$-terms, the cross coupling of the two sectors at an intermediate scale can push the metastable vacuum outside of the regime of the effective field theory. We parametrize the region in which the metastable vacua are safe. We then show that sufficiently small cross couplings can be made natural. Finally, we briefly discuss the role of moduli in stringy realizations of retrofitted SUSY-breaking sectors.

We consider the constrained zero modes found in the application of discrete light-cone quantization to the nonperturbative solution of quantum field theories. These modes are usually neglected for simplicity, but we show that their inclusion can be relatively straightforward, and, what is more, that they are useful for nonperturbative calculations of field-theoretic spectra. In particular, inclusion of zero modes improves the convergence of the numerical calculation and makes possible the direct calculation of vacuum expectation values, even when the zero modes are determined dynamically. We also comment on zero-mode contributions not included by discrete light-cone quantization, namely, zero-mode loops.

The defining feature of scalar sequestering is that the minimal supersymmetric standard model squark and slepton masses as well as all entries of the scalar Higgs mass matrix vanish at some high scale. This ultraviolet boundary condition—scalar masses vanish while gaugino and Higgsino masses are unsuppressed—is independent of the supersymmetry breaking mediation mechanism. It is the result of renormalization group scaling from approximately conformal strong dynamics in the hidden sector. We review the mechanism of scalar sequestering and prove that the same dynamics which suppresses scalar soft masses and the $B_{\mu }$ term also drives the Higgs soft masses to $-|\mu {|}^2$. Thus the supersymmetric contribution to the Higgs mass matrix from the $\mu$ term is exactly canceled by the soft masses. Scalar sequestering has two tell-tale predictions for the superpartner spectrum in addition to the usual gaugino mediation predictions: Higgsinos are much heavier ($\mu \gtrsim \mathrm{TeV}$) than scalar Higgses ($m_A\sim \mathrm{\text{few hundred}}\mathrm{GeV}$), and third generation scalar masses are enhanced because of new positive contributions from Higgs loops.

The minimal supergravity model predicts the polarization of the tau coming from the stau to bino decay in the co-annihilation region to be $+1$. This can be exploited to extract this soft tau signal at LHC and also to measure the tiny mass differences between the stau and the bino lightest superparticle. Moreover, this strategy will be applicable for a wider class of bino lightest superparticle models, where the lighter stau has a right component at least of similar size as the left.

In this work, we examine a two-Higgs-doublet extension of the standard model in which one Higgs doublet is responsible for giving mass to both up- and down-type quarks, while a separate doublet is responsible for giving mass to leptons. We examine both the theoretical and experimental constraints on the model and show that large regions of parameter space are allowed by these constraints in which the effective couplings between the lightest neutral Higgs scalar and the standard-model leptons are substantially enhanced. We investigate the collider phenomenology of such a “leptophilic” two-Higgs-doublet model and show that in cases where the low-energy spectrum contains only one light, $CP$-even scalar, a variety of collider processes essentially irrelevant for the discovery of a standard model Higgs boson (specifically those in which the Higgs boson decays directly into a charged-lepton pair) can contribute significantly to the discovery potential of a light-to-intermediate-mass ($m_h\lesssim 140\mathrm{GeV}$) Higgs boson at the LHC.

We have considered nonuniversal gaugino mass models of supergravity, arising from a mixture of two superfield contributions to the gauge kinetic term, belonging to a singlet and a nonsinglet representation of the grand unified theory group. In particular we analyze two models, where the contributing superfields belong to the singlet and the 75-dimensional, and the singlet and the 200-dimensional representations of $SU(5)$. The resulting lightest superparticle is a mixed bino-Higgsino state in the first case and a mixed bino-wino-Higgsino state in the second. In both cases one obtains cosmologically compatible dark matter relic density over broad regions of the parameter space. We predict promising signals in direct dark matter detection experiments as well as in indirect detection experiments via high energy neutrinos coming from their pair annihilation in the Sun. Besides, we find interesting $\gamma$-ray signal rates that will be probed in the Fermi gamma-ray space telescope. We also expect promising collider signals at LHC in both cases.

Twin Higgs models are economical extensions of the standard model that stabilize the electroweak scale. In these theories the Higgs field is a pseudo Nambu-Goldstone boson that is protected against radiative corrections up to scales of order 5 TeV by a discrete parity symmetry. We construct, for the first time, a class of composite twin Higgs models based on confining QCD-like dynamics. These theories naturally incorporate a custodial isospin symmetry and predict a rich spectrum of particles with masses of order a TeV that will be accessible at the LHC.

We present our results for the on-shell $\Delta I=3/2$ kaon decay matrix elements using domain wall fermions and the DBW2 gauge action at one coarse lattice spacing corresponding to $a^{-1}=1.31\mathrm{GeV}$ in the quenched approximation. The on-shell matrix elements are evaluated in two different frames: the center-of-mass frame and nonzero total-momentum frame. We employ the formula proposed by Lellouch and Lüscher in the center-of-mass frame, and its extension for a nonzero total-momentum frame to extract the infinite volume, on-shell, center-of-mass frame decay amplitudes. We determine the decay amplitude at the physical pion mass and momentum from the chiral extrapolation and an interpolation of the relative momentum using the results calculated in the two frames. We have obtained $\mathrm{Re}{A}_2=1.66(23)(\genfrac{}{}{0ex}{}{+48}{-03})(\genfrac{}{}{0ex}{}{+53}{-0})\times {10}^{-8}\mathrm{GeV}$ and $\mathrm{Im}{A}_2=-1.181(26)(\genfrac{}{}{0ex}{}{+141}{-014})(\genfrac{}{}{0ex}{}{+44}{-0})\times {10}^{-12}\mathrm{GeV}$ at the physical point, using the data at the relatively large pion mass, $m_{\pi }>0.35\mathrm{GeV}$. The first error is statistic, and the second and third are systematic. The second error is estimated with several fits of the chiral extrapolation including the (quenched) chiral perturbation formula at next to leading order using only lighter pion masses. The third one is estimated with an analysis using the lattice dispersion relation. The result of $\mathrm{Re}{A}_2$ is reasonably consistent with experiment.

We calculate the SU(3)-breaking corrections to the hyperon vector coupling $f_1(0)$ up to $\mathcal{O}(p^4)$ in covariant baryon chiral perturbation theory with dynamical octet and decuplet contributions. We find that the decuplet contributions are of similar or even larger size than the octet ones. Combining both, we predict positive SU(3)-breaking corrections to all the four independent $f_1(0)$’s (assuming isospin symmetry), which are consistent, within uncertainties, with the latest results from large $N_c$ fits, chiral quark models, and quenched lattice QCD calculations.

In the framework of generalized parton distributions, we study the helicity-dependent and independent cross sections measured in Hall A and the beam spin asymmetries measured in Hall B at Jefferson Laboratory. We perform a global fit of these data and fits on each kinematic bin. We extract the real and imaginary parts of the Compton form factor $\mathcal{H}$ under the main hypothesis of dominance of the generalized parton distribution $H$ and twist 2 accuracy. We discuss our results and compare to previous extractions as well as to the VGG model. We pay extra attention to the estimation of errors on the extraction of $\mathcal{H}$.

A hybrid meson is a quark-antiquark pair in which, contrary to ordinary mesons, the gluon field is in an excited state. In the framework of constituent models, the interaction potential is assumed to be the energy of an excited string. An approximate, but accurate, analytical solution of the Schrödinger equation with such a potential is presented. When applied to hybrid charmonia and bottomonia, towers of states are predicted in which the masses are a linear function of a harmonic oscillator band number for the quark-antiquark pair. Such a formula could be a reliable guide for the experimental detection of heavy hybrid mesons.

We investigate diffractive events in hadron-hadron collisions, in which two jets are produced and separated by a large rapidity gap. In perturbative QCD, the hard color-singlet object exchanged in the $t$ channel, and responsible for the rapidity gap, is the Balitsky-Fadin-Kuraev-Lipatov Pomeron. We perform a phenomenological study including the corrections due to next-to-leading logarithms. Using a renormalization-group improved next-to-leading logarithmic kernel, we show that the Balitsky-Fadin-Kuraev-Lipatov predictions are in good agreement with the Tevatron data and present predictions which could be tested at the LHC.