In phenomenological studies of low-energy supersymmetry, running gaugino masses are often taken to be equal near the scale of apparent gauge coupling unification. However, many known mechanisms can avoid this universality, even in models with unified gauge interactions. One example is an $F$-term vacuum expectation value that is a singlet under the standard model gauge group but transforms nontrivially in the symmetric product of two adjoint representations of a group that contains the standard model gauge group. Here, I compute the ratios of gaugino masses that follow from $F$-terms in nonsinglet representations of $SO(10)$ and $E_6$ and their subgroups, extending well-known results for $SU(5)$. The $SO(10)$ results correct some long-standing errors in the literature.

We have performed a systematical calculation of the pion ($\pi$, $K$, $\eta$) and heavy pseudoscalar meson $S$-wave scattering lengths up to $\mathcal{O}(p^3)$ in the chiral perturbation theory in the heavy quark symmetry limit. With the three scattering lengths from the lattice simulations as input we estimate the unknown low-energy constants. Then we predict all the other unmeasured scattering lengths. The analytical expressions and predictions may be helpful to future investigations. Especially we note that the $DK$ scattering length is positive. Therefore their interaction is attractive, which helps to lower the mass of the bare charm-strange scalar state in the quark model through the couple-channel effect.

We examine the electromagnetic properties of the $\Delta (1232)$ resonance within the self-consistent chiral quark-soliton model. In particular, we present the $\Delta$ form factors of the vector-current $G_{E0}(Q^2)$, $G_{E2}(Q^2)$, and $G_{M1}(Q^2)$ for a momentum-transfer range of $0\le Q^2\le 1{\mathrm{GeV}}^2$. We apply the symmetry-conserving quantization of the soliton and take $1/N_c$ rotational corrections into account. Values for the magnetic moments of all decuplet baryons as well as for the $N-\Delta$ transition are given. Special attention is also given to the electric quadrupole moment of the $\Delta$.

We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of $1.9{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions collected at $\sqrt{s}=1.96\mathrm{TeV}$ with the CDF II detector at Fermilab’s Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a nonparametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the $W$ decay in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel, and the top quark mass and the scalar sum of transverse energy of the event in the dilepton channel. We perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic $W$ boson mass. Using 332 $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ candidate events and 144 dilepton candidate events, we measure the top quark mass to be $M_{\mathrm{top}}=171.9\pm 1.7(\mathrm{stat}+\mathrm{JES})\pm 1.1(\mathrm{\text{other}}\mathrm{syst})\mathrm{GeV}/c^2=171.9\pm 2.0\mathrm{GeV}/c^2$.

We discuss a method of calculating the various scalar densities encountered in Lovelock theory, which relies on diagrammatic, instead of algebraic manipulations. Taking advantage of the known symmetric and antisymmetric properties of the Riemann tensor that appears in the Lovelock densities, we map every quadratic or higher contraction into a corresponding permutation diagram. The derivation of the explicit form of each density is then reduced to identifying the distinct diagrams, from which we can also read off the overall combinatoric factors. The method is applied to the first Lovelock densities, of order two (Gauss-Bonnet term) and three.

In this paper we present a family of supersymmetric Wilson loops of $\mathcal{N}=4$ supersymmetric Yang-Mills theory in Minkowski space. Our examples focus on curves restricted to hyperbolic submanifolds, ${\mathbb{H}}_3$ and ${\mathbb{H}}_2$, of space-time. Generically they preserve two supercharges, but in special cases more, including a case which has not been discussed before, of the hyperbolic line, conformal to the straight line and circle, which is $1/2$ BPS. We discuss some general properties of these Wilson loops and their string duals and study special examples in more detail. Generically the string duals propagate on a complexification of ${\mathrm{AdS}}_5\times S^5$ and in some specific examples the compact sphere is effectively replaced by a de Sitter space.

We analyze aspects of symmetry breaking for Moyal spacetimes within a quantization scheme which preserves the twisted Poincaré symmetry. Towards this purpose, we develop the Lehmann-Symanzik-Zimmermann (LSZ) approach for Moyal spacetimes. The latter gives a formula for scattering amplitudes on these spacetimes which can be obtained from the corresponding ones on the commutative spacetime. This formula applies in the presence of spontaneous breakdown of symmetries as well. We also derive Goldstone’s theorem on Moyal spacetime. The formalism developed here can be directly applied to the twisted standard model.

In quantum mechanics the deterministic property of classical physics is an emergent phenomenon appropriate only on macroscopic scales. Lee and Wick introduced Lorentz invariant quantum theories where causality is an emergent phenomenon appropriate for macroscopic time scales. In this paper we analyze a Lee-Wick version of the $O(N)$ model. We argue that in the large-$N$ limit this theory has a unitary and Lorentz invariant $S$ matrix and is therefore free of paradoxes in scattering experiments. We discuss some of its acausal properties.

We present an algorithm for writing down explicit formulas for all tree amplitudes in $\mathcal{N}=8$ supergravity, obtained from solving the supersymmetric on-shell recursion relations. The formula is patterned after one recently obtained for all tree amplitudes in $\mathcal{N}=4$ super Yang-Mills theory which involves nested sums of dual superconformal invariants. We find that all graviton amplitudes can be written in terms of exactly the same structure of nested sums with two modifications: the dual superconformal invariants are promoted from $\mathcal{N}=4$ to $\mathcal{N}=8$ superspace in the simplest manner possible—by squaring them—and certain additional nondual conformal gravity dressing factors (independent of the superspace coordinates) are inserted into the nested sums. To illustrate the procedure we give explicit closed-form formulas for all NMHV, NNMHV and NNNMV gravity superamplitudes.

We consider how accelerated expansion, whether due to inflation or dark energy, imposes strong constraints on fundamental theories obtained by compactification from higher dimensions. For theories that obey the null energy condition (NEC), we find that inflationary cosmology is impossible for a wide range of compactifications; and a dark energy phase consistent with observations is only possible if both Newton’s gravitational constant and the dark energy equation of state vary with time. If the theory violates the NEC, inflation and dark energy are only possible if the NEC-violating elements are inhomogeneously distributed in the compact dimensions and vary with time in precise synchrony with the matter and energy density in the noncompact dimensions. Although our proofs are derived assuming general relativity applies in both four and higher dimensions and certain forms of metrics, we argue that similar constraints must apply for more general compactifications.

We study the stability of static black holes in the third order Lovelock theory. We derive a master equation for tensor perturbations. Using the master equation, we analyze the stability of Lovelock black holes mainly in seven and eight dimensions. We find there are cases where the linear analysis breaks down. If we restrict ourselves to the regime where the linear analysis is legitimate, black holes are always stable in seven dimensions. However, in eight dimensions, there exists a critical mass below which black holes are unstable. Combining our result in the third order Lovelock theory with the previous one in Einstein-Gauss-Bonnet theory, we conjecture that small black holes are unstable in any dimensions. The instability found in this paper will be important for the analysis of black holes at the LHC.

Warm dark matter (WDM) may resolve the possible conflict between observed galaxy halos and the halos produced in cold dark matter simulations. Here, we present an extension of the minimal supersymmetric standard model to include WDM by adding a gauge singlet fermion, $\overline{\chi }$, with a portal-like coupling to the minimal supersymmetric standard model Higgs doublets. This model has the property that the dark matter is necessarily warm. In the case where $M_{\overline{\chi }}$ is mainly due to electroweak symmetry breaking, the $\overline{\chi }$ mass is completely determined by its relic density and the reheating temperature $T_R$. For ${10}^2\mathrm{GeV}\lesssim T_R\lesssim {10}^5\mathrm{GeV}$, the range allowed by $\overline{\chi }$ production via thermal Higgs annihilation, the $\overline{\chi }$ mass is in the range 0.3–4 keV, precisely the range required for WDM. The primordial phase-space density $Q$ can directly account for that observed in dwarf spheroidal galaxies, $Q\approx 5\times {10}^6(\mathrm{eV}/\mathrm{c}{\mathrm{m}}^3)/(\mathrm{km}/\mathrm{s}{)}^3$, when the reheating temperature is in the range $T_R\approx 10–100\mathrm{TeV}$, in which case $M_{\overline{\chi }}\approx 0.45\mathrm{keV}$. The free-streaming length is in the range 0.3–4 Mpc, which can be small enough to alleviate the problems of overproduction of galaxy substructure and low angular momentum of cold dark matter simulations.

We investigate a cosmological model, based on the Salam-Sezgin six-dimensional supergravity theory and on previous work by Anchordoqui, Goldberg, Nawata, and Nuñez. Assuming a period of warm inflation, we show that it is possible to extend the evolution of the model back in time, to include the inflationary period, thus unifying inflation, dark matter, and dark energy within a single framework. Like the previous authors, we were not able to obtain the full dark matter content of the universe from the Salam-Sezgin scalar fields. However, even if only partially successful, this work shows that present-day theories, based on superstrings and supergravity, may eventually lead to a comprehensive modeling of the evolution of the universe. We find that the gravitational-wave spectrum of the model has a nonconstant negative slope in the frequency range $({10}^{-15}–{10}^6)\mathrm{rad}/\mathrm{s}$, and that, unlike standard (cold) inflation models, it shows no structure in the $\mathrm{MHz}/\mathrm{GHz}$ range of frequencies.

We investigate in detail the possibility that a single imperfect fluid with bulk viscosity can replace the need for separate dark matter and dark energy in cosmological models. With suitable choices of model parameters, we show that the background cosmology in this model can mimic that of a $\Lambda \mathrm{CDM}$ universe to high precision. However, as the cosmic expansion goes through the decelerating-accelerating transition, the density perturbations in this fluid are rapidly damped out. We show that, although this does not significantly affect structure formation in baryonic matter, it makes the gravitational potential decay rapidly at late times, leading to modifications in predictions of cosmological observables such as the CMB power spectrum and weak lensing. This model of unified dark matter is thus difficult to reconcile with astronomical observations. We also clarify the differences with respect to other unified dark matter models where the fluid is barotropic, i.e., $p=p(\rho )$, such as the (generalized) Chaplygin gas model, and point out their observational difficulties. We also summarize the status of dark sector models with no new dynamical degrees of freedom introduced and discuss the problems with them.

We reply to the preceding comment by E. van Beveren et al. [E. van Beveren, F. Kleefeld, G. Rupp, and M. D. Scadron, Phys. Rev. D 79, 098501 (2009)].

We comment on a recent paper by Giacosa, Gutsche, and Lyobovitskij [Phys. Rev. D 77, 034007 (2008)], in which it is argued that a quarkonium interpretation of the $\sigma$ meson should give rise to a much smaller two-photon decay width than commonly assumed. The reason for this claimed discrepancy is a term in the transition amplitude, necessary for gauge invariance, which allegedly is often omitted in the literature, including the work of the present authors. Here we show their claims to be incorrect by demonstrating, in the context of the quark-level linear $\sigma$ model, that the recently extracted experimental values are compatible with a $q\overline{q}$ assignment for the $\sigma$, provided that meson loops are taken into account as well.

The study of electron-positron collisions at center-of-mass (c.m.) energies corresponding to charmonium production has reached new levels of sensitivity thanks to experiments by the BES and CLEO Collaborations. Final states $\gamma P$, where $P$ is a pseudoscalar meson such as ${\pi }^0$, $\eta$, and ${\eta }^{\prime }$ can arise either from charmonium decays or in the continuum through a virtual photon: $e^{+}{e}^{-}\to {\gamma }^{*}\to \gamma P$. Estimates of this latter process are given at c.m. energies corresponding to the $J/\psi (1S)$, $\psi (2S)$, and $\psi (3770)$ resonances.

It is often true that an invariant mass constructed from visible decay products of a heavy particle may attain a maximum(or minimum) for a certain kinematic configuration only—this fact can be used to reconstruct relevant particle masses from observed decay product momenta of events near the invariant mass endpoint. Motivated minimal supersymmetric standard model neutralino and chargino mass reconstruction at the LHC from multilepton endstates is illustrated by way of example.

With the first measurements of the branching ratios and the direct $CP$ asymmetries of $B_s\to K^{-}{K}^{+}$, $K^{-}{\pi }^{+}$ decays by the CDF collaboration, we constrain the relevant parameter space of the minimal supersymmetric standard model with R-parity violation. Using the constrained R-parity violating couplings, we further examine their possible effects in $B_s\to K^{-*}{\pi }^{+}$, $K^{(*)-}{\rho }^{+}$ and $K^{(*)\pm }{K}^{(*)\mp }$ decays. We find that some branching ratios and $CP$ asymmetries are very sensitive to the R-parity violating couplings. The direct longitudinal $CP$ asymmetries of tree-dominated process $B_s\to K^{*-}{\rho }^{+}$ could be enlarged to $\sim 70\%$ and the longitudinal polarizations of $B_s\to K^{*-}{K}^{*+}$, $K^{*-}{\rho }^{+}$ decays could be suppressed very much by the squark exchange couplings. Near future experiments at CERN LHC can test these predictions and shrink/reveal the parameter spaces of RPV SUSY.

Using the $B\to K_1$ form factors evaluated in the perturbative QCD approach, we study semileptonic $B\to K_1(1270)l^{+}{l}^{-}$ and $B\to K_1(1400)l^{+}{l}^{-}$ decays, where $K_1(1270)$ and $K_1(1400)$ are mixtures of $K_{1A}$ and $K_{1B}$ which are ${}^{3}P_1$ and ${}^{1}P_1$ states, respectively. Using the technique of helicity amplitudes, we express the decay amplitudes in terms of several independent and Lorentz invariant pieces. We study the dilepton invariant mass distributions, branching ratios, polarizations, and forward-backward asymmetries of $B\to K_1{l}^{+}{l}^{-}$ decays. The ambiguity in the sign of the mixing angle will induce very large differences to branching ratios of semileptonic $B$ decays: branching ratios without resonant contributions either have the order of ${10}^{-6}$ or ${10}^{-8}$. But the polarizations and the forward-backward asymmetries are not sensitive to the mixing angles. We find that the resonant contributions will dramatically change the dilepton invariant mass distributions in the resonant region. We also provide the angular distributions of $B\to K_1{l}^{+}{l}^{-}\to (K\pi \pi )l^{+}{l}^{-}$ decays.