We calculate the $CP$-averaged branching ratios and $CP$-violating asymmetries for the two-body charmless hadronic decays ${\Lambda }_b\to p\pi$, $pK$ in the perturbative QCD (pQCD) approach to lowest order in ${\alpha }_s$. The baryon distribution amplitudes involved in the factorization formulas are considered to the leading twist accuracy, and the distribution amplitudes of the proton are expanded to the next-to-leading conformal spin (i.e., “P” waves), the moments of which are determined from QCD sum rules. Our work shows that the contributions from the factorizable diagrams in ${\Lambda }_b\to p\pi$, $pK$ decays are much smaller compared to the nonfactorizable diagrams in the conventional pQCD approach. We argue that this reflects the estimates of the ${\Lambda }_b\to p$ transition form factors in the $k_T$ factorization approach, which are found to be typically an order of magnitude smaller than those estimated in the light-cone sum rules and in the nonrelativistic quark model. As an alternative, we adopt a hybrid pQCD approach, in which we compute the factorizable contributions with the ${\Lambda }_b\to p$ form factors taken from the light-cone QCD sum rules. The nonfactorizable diagrams are evaluated utilizing the conventional pQCD formalism, which is free from the endpoint singularities. The predictions worked out here are confronted with the recently available data from the CDF Collaboration on the branching ratios and the direct $CP$ asymmetries for the decays ${\Lambda }_b\to p\pi$ and ${\Lambda }_b\to pK$. The asymmetry parameter $\alpha$ relevant for the anisotropic angular distribution of the emitted proton in the polarized ${\Lambda }_b$ baryon decays is also calculated for the two decay modes.

Dominant spin-flip effects for the direct and prompt $J/\psi$ polarizations at Tevatron run II with collision energy 1.96 TeV and rapidity cut $|y^{J/\psi }|<0.6$ are systematically studied. The spin-flip effect for the transition of $(c\overline{c}{)}_8[{}^{3}S_1]$ into $J/\psi$ is especially discussed with care. It is found that the spin-flip effect shall always dilute the $J/\psi$ polarization, and with a suitable choice of the parameters $a_{0,1}$ and $c_{0,1,2}$, the $J/\psi$ polarization puzzle can be solved to a certain degree. At large transverse momentum $p_t$, $\alpha$ for the prompt $J/\psi$ is reduced by $\sim 50\%$ for $f_0=v^2$ and by $\sim 80\%$ for $f_0=1$. We also study the indirect $J/\psi$ polarization from the $b$ decays, which however is slightly affected by the same spin-flip effect and then shall provide a better platform to determine the color-octet matrix elements.

We investigate the Compton scattering vertex of charged scalars and photons in scalar quantum electrodynamics (SQED). We carry out its nonperturbative construction consistent with Ward-Fradkin-Green-Takahashi identity which relates 3-point vertices to the 4-point ones. There is an undetermined part which is transverse to one or both the external photons, and needs to be evaluated through perturbation theory. We present in detail how the transverse part at the 1-loop order can be evaluated for completely general kinematics of momenta involved in covariant gauges and dimensions. This involves the calculation of genuine 4-point functions with three massive propagators, the most nontrivial integrals reported in this paper. We also discuss possible applications of our results.

We continue the study of model-independent constraints on the unitary conformal field theories (CFTs) in four dimensions, initiated in [R. Rattazzi, V. S. Rychkov, E. Tonni, and A. Vichi, J. High Energy Phys. 12 (2008) 031]. Our main result is an improved upper bound on the dimension $\Delta$ of the leading scalar operator appearing in the operator product expansion (OPE) of two identical scalars of dimension $d$: ${\varphi }_d\times {\varphi }_d=\mathbb{1}+O_{\Delta }+\dots$. In the interval $1<d<1.7$ this universal bound takes the form $\Delta \le 2+0.7(d-1{)}^{1/2}+2.1(d-1)+0.43(d-1{)}^{3/2}$. The proof is based on prime principles of CFT: unitarity, crossing symmetry, OPE, and conformal block decomposition. We also discuss possible applications to particle phenomenology and, via a 2D analogue, to string theory.

Modifications to the classic time-delay effect and Doppler shift in general relativity (GR) are studied in the context of the Lorentz-violating standard-model extension (SME). We derive the leading Lorentz-violating corrections to the time-delay and Doppler shift signals, for a light ray passing near a massive body. It is demonstrated that anisotropic coefficients for Lorentz violation control a time-dependent behavior of these signals that is qualitatively different from the conventional case in GR. Estimates of sensitivities to gravity-sector coefficients in the SME are given for current and future experiments, including the recent Cassini solar conjunction experiment.

We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati (DGP) braneworld model, by solving the full nonlinear equations of motion for the scalar degree of freedom in this model, the brane-bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes nonlinear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to general relativity. The code uses a multigrid relaxation scheme to solve the nonlinear field equation in the quasistatic approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. However, the type of nonlinear interactions of the brane-bending mode, which are the focus of this study, are generic to a wide class of braneworld cosmologies. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane-bending mode. This allows us to isolate the effects of the nonlinear self-couplings of the field which are noticeable already on quasilinear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane-bending mode within cosmological structure formation. We find that, independently of cosmic microwave background constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.

In this work, we analyze the implications of graviton-to-photon conversion in the presence of large scale magnetic fields. We consider the magnetic fields associated with galaxy clusters, filaments in the large scale structure, as well as primordial magnetic fields. We analyze the interaction of these magnetic fields with an exogenous high-frequency gravitational wave (HFGW) background which may exist in the Universe. We show that, in the presence of the magnetic fields, a sufficiently strong HFGW background would lead to an observable signature in the frequency spectrum of the cosmic microwave background. The sensitivity of current day cosmic microwave background experiments allows one to place significant constraints on the strength of the HFGW background, ${\Omega }_{\mathrm{GW}}\lesssim 1$. These limits are about 25 orders of magnitude stronger than currently existing direct constraints in this frequency region.

Soft gamma repeaters (SGRs) have unique properties that make them intriguing targets for gravitational wave (GW) searches. They are nearby, their burst emission mechanism may involve neutron star crust fractures and excitation of quasinormal modes, and they burst repeatedly and sometimes spectacularly. A recent LIGO search for transient GW from these sources placed upper limits on a set of almost 200 individual SGR bursts. These limits were within the theoretically predicted range of some models. We present a new search strategy which builds upon the method used there by “stacking” potential GW signals from multiple SGR bursts. We assume that variation in the time difference between burst electromagnetic emission and burst GW emission is small relative to the GW signal duration, and we time-align GW excess power time-frequency tilings containing individual burst triggers to their corresponding electromagnetic emissions. Using Monte Carlo simulations, we confirm that gains in GW energy sensitivity of $N^{1/2}$ are possible, where $N$ is the number of stacked SGR bursts. Estimated sensitivities for a mock search for gravitational waves from the 2006 March 29 storm from SGR 1900+14 are also presented, for two GW emission models, “fluence-weighted” and “flat” (unweighted).

We compute the simplest hard thermal loops for a spatial ’t Hooft loop in the deconfined phase of a $\mathrm{SU}(N)$ gauge theory. We expand to quadratic order about a constant background field $A_0=Q/g$, where $Q$ is a diagonal, color matrix and $g$ is the gauge coupling constant. We analyze the problem in sufficient generality that the techniques developed can be applied to compute transport properties in a “semi”-quark gluon plasma. Notably, computations are done using the double line notation at finite $N$. The quark self-energy is a $Q$-dependent thermal mass squared $\sim g^2{T}^2$, where $T$ is the temperature, times the same hard thermal loop as at $Q=0$. The gluon self-energy involves two pieces: a $Q$-dependent Debye mass squared, $\sim g^2{T}^2$, times the same hard thermal loop as for $Q=0$, plus a new hard thermal loop $\sim g^2{T}^3$, due to the color electric field generated by a spatial ’t Hooft loop.

We study bulk fermions in models with warped extra dimensions in the presence of a soft wall. Fermions can acquire a position dependent bulk Dirac mass that shields them from the deep infrared, allowing for a systematic expansion in which electroweak symmetry breaking effects are treated perturbatively. Using this expansion, we analyze properties of bulk fermions in the soft-wall background. These properties include the realization of nontrivial boundary conditions that simulate the ones commonly used in hard-wall models, the analysis of the flavor structure of the model and the implications of a heavy top. We implement a soft-wall model of electroweak symmetry breaking with custodial symmetry and fermions propagating in the bulk. We find a lower bound on the masses of the first bosonic resonances, after including the effects of the top sector on electroweak precision observables for the first time, of $m_{KK}\gtrsim 1–3\mathrm{TeV}$ at the 95% C.L., depending on the details of the Higgs, and discuss the implications of our results for LHC phenomenology.

Within the framework of supersymmetry, the particle content is extended in a way that each Higgs doublet is in a full generation. Namely, in addition to ordinary three generations, there is an extra vectorlike generation, and it is the extra slepton $\mathrm{SU}(2{)}_L$ doublets that are taken to be the two Higgs doublets. $R$-parity violating interactions contain ordinary Yukawa interactions. Breaking of supersymmetry and gauge symmetry are analyzed. Fermion and boson spectra are calculated. Phenomenological constraints and relevant new physics at Large Hadron Collider are discussed.

Flavor changing neutral currents arise in the $SU(3{)}_c\otimes SU(4{)}_L\otimes U(1{)}_X$ extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the $Z$ pole, atomic parity violation data, and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales $M_{Z_2}$ and $M_{Z_3}$ of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on $M_{Z_2}$ and $M_{Z_3}$ as low as possible without violating experimental constraints.

In this work, we study the radiative open-charm decays $Y(4140)\to D_s^{*+}{D}_s^{-}\gamma$ and $Y(3930)\to D^{*+}{D}^{-}\gamma$ under the assignments of $D_s^{*}{\overline{D}}_s^{*}$ and $D^{*}{\overline{D}}^{*}$ as molecular states for $Y(4140)$ and $Y(3930)$, respectively. Based on our numerical result, we propose the experimental measurement of the photon spectrum of $Y(4140)\to D_s^{*+}{D}_s^{-}\gamma$, $D_s^{+}{D}_s^{*-}\gamma$ and $Y(3930)\to D^{*0}{\overline{D}}^0\gamma$, $D^0{\overline{D}}^{*0}\gamma$, $D^{*+}{D}^{-}\gamma$, $D^{+}{D}^{*-}\gamma$ can further test the molecular assignment for $Y(4140)$ and $Y(3930)$.

The differential cross section for the process $\gamma \gamma \to \eta {\pi }^0$ has been measured in the kinematic range $0.84\mathrm{GeV}<W<4.0\mathrm{GeV}$, $|\cos {\theta }^{*}|<0.8$, where $W$ and ${\theta }^{*}$ are the energy and ${\pi }^0$ (or $\eta$) scattering angle, respectively, in the $\gamma \gamma$ center-of-mass system. The results are based on a $223{\mathrm{fb}}^{-1}$ data sample collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. Clear peaks due to the $a_0(980)$ and $a_2(1320)$ are visible. The differential cross sections are fitted in the energy region $0.9\mathrm{GeV}<W<1.46\mathrm{GeV}$ to obtain the parameters of the $a_0(980)$. Its mass, width and ${\Gamma }_{\gamma \gamma }\mathcal{B}(\eta {\pi }^0)$ are measured to be ${982.3}_{-0.7-4.7}^{+0.6+3.1}\mathrm{MeV}/c^2$, $75.6\pm {1.6}_{-10.0}^{+17.4}\mathrm{MeV}$ and ${128}_{-2-43}^{+3+502}\mathrm{eV}$, respectively. The energy and angular dependences above 3.1 GeV are compared with those measured in the ${\pi }^0{\pi }^0$ channel. The integrated cross section over $|\cos {\theta }^{*}|<0.8$ has a $W^{-n}$ dependence with $n=10.5\pm 1.2\pm 0.5$, which is slightly larger than that for ${\pi }^0{\pi }^0$. The differential cross sections show a ${sin}^{-4}{\theta }^{*}$ dependence similar to $\gamma \gamma \to {\pi }^0{\pi }^0$. The measured cross section ratio, $\sigma (\eta {\pi }^0)/\sigma ({\pi }^0{\pi }^0)=0.48\pm 0.05\pm 0.04$, is consistent with a QCD-based prediction.

From a Dalitz plot analysis of $B\to K{\pi }^{+}{\psi }^{\prime }$ decays, we find a signal for $Z(4430{)}^{+}\to {\pi }^{+}{\psi }^{\prime }$ with a mass $M=({4443}_{-12-13}^{+15+19})\mathrm{MeV}/c^2$, width $\Gamma =({107}_{-43-56}^{+86+74})\mathrm{MeV}$, product branching fraction $\mathcal{B}({\overline{B}}^0\to K^{-}Z(4430{)}^{+})\times \mathcal{B}(Z(4430{)}^{+}\to {\pi }^{+}{\psi }^{\prime })=({3.2}_{-0.9-1.6}^{+1.8+5.3})\times {10}^{-5}$, and significance of $6.4\sigma$ that agrees with previous Belle measurements based on the same data sample. In addition, we determine the branching fraction $\mathcal{B}(B^0\to K^{*}(892{)}^0{\psi }^{\prime })=({5.52}_{-0.32-0.58}^{+0.35+0.53})\times {10}^{-4}$ and the fraction of $K^{*}(892{)}^0$ mesons that are longitudinally polarized $f_L=({44.8}_{-2.7-5.3}^{+4.0+4.0})\%$. These results are obtained from a $605{\mathrm{fb}}^{-1}$ data sample that contains $657\times {10}^6$ $B\overline{B}$ pairs collected near the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

Matos, Guzmán, and Nuñez proposed a model for the galactic halo within the framework of scalar field theory. We argue that an analysis involving the full metric can reveal the true physical nature of the halo only when a certain condition is maintained. We fix that condition and also calculate its impact on observable parameters of the model.

We extend the dimensional deconstruction by utilizing the knowledge of graph theory. In the dimensional deconstruction, one uses the moose diagram to exhibit the structure of the “theory space.” We generalize the moose diagram to a general graph with oriented edges. In the present paper, we consider only the $U(1)$ gauge symmetry. We also introduce supersymmetry into our model by use of superfields. We suppose that vector superfields reside at the vertices and chiral superfields at the edges of a given graph. Then we can consider multivector, multi-Higgs models. In our model, $[U(1){]}^p$ (where $p$ is the number of vertices) is broken to a single $U(1)$. Therefore, for specific graphs, we get vortexlike classical solutions in our model. We show some examples of the graphs admitting the vortex solutions of simple structure as the Bogomolnyi solution.

The interaction between Chern-Simons (CS) theories and localized external sources ($2p$-branes) is analyzed. This interaction generalizes the minimal coupling between a point charge (0-brane) and a gauge connection. The external currents that define the $2p$ branes are covariantly constant ($D-2p-1$)-forms coupled to ($2p-1$) CS forms. The general expression for the sources—charged with respect to the corresponding gauge algebra—is presented, focusing on two special cases: 0-branes and ($D-3$)-branes. In any dimension, 0-branes are constructed as topological defects produced by a surface deficit of ($D-2$)-sphere in anti-de Sitter space, and they are not constant curvature spaces for $D>3$. They correspond to dimensionally continued black holes with negative mass. On the other hand, in the case of CS (super) gravities, the ($D-3$)-branes are naked conical singularities (topological defects) obtained by identification of points with a Killing vector. In $2+1$ dimensions, extremal spinning branes of this type are Bogomol’nyi-Prasad-Sommerfield states. Stable ($D-3$)-branes are shown to exist also in higher dimensions, as well. Classical field equations are also discussed, and in the presence of sources there is a large number of inequivalent and disconnected sectors in solution space.

Two general problems arise when interpreting the recent cosmic ray data as signals of dark matter (DM) annihilation: (i) the required cross section is too large by $\mathcal{O}(100)$, and (ii) the annihilation products seem to be mostly leptonic. We propose to address these two problems by assuming that the couplings of DM to leptons grow with time. This can be achieved by a dynamic localization of DM in extra dimensions. A possible outcome of this proposal is a time (redshift) dependent annihilation signal, in terms of strength and dominant final states.

Strongly coupled semidirect gauge mediation models of supersymmetry breaking through massive mediators with standard-model charges are investigated by means of composite degrees of freedom. Sizable mediation is realized to generate the standard-model gaugino masses for a small mediator mass without breaking the standard-model symmetries.