We consider extra-dimensional descriptions of models where there are two separate strongly interacting sectors contributing to electroweak symmetry breaking (“topcolor” type models). In the extra-dimensional picture there would be two separate (anti-de Sitter) bulks meeting on the Planck brane, with each bulk having its own corresponding IR (TeV) brane. Sources for electroweak symmetry breaking can then be localized on both of these IR branes, while the different generations of fermions may be separated from each other. We describe the modes propagating in such a setup, and consider the cases where the electroweak symmetry breaking on either of the two IR branes come either from a Higgsless scenario (via boundary conditions) or a (top-)Higgs. We show that the tension that exists between obtaining a large top quark mass and the correct value of the $Zb\overline{b}$ couplings in ordinary Higgsless models can be largely relieved in the Higgsless–top-Higgs versions of the two IR brane models. This may also be true in the purely Higgsless–Higgsless case, however since that model is necessarily in the strongly coupled regime the tree-level results for the properties of the third generation may get large corrections. A necessary consequence of such models is the appearance of additional pseudo-Goldstone bosons (“top-pions”), which would be strongly coupled to the third generation.

We discuss a possible new resonance in active-sterile neutrino oscillations arising in theories with large extra dimensions. Fluctuations in the brane effectively increase the path-length of active neutrinos relative to the path-length of sterile neutrinos through the extra-dimensional bulk. Well below the resonance, the standard oscillation formulas apply. Well above the resonance, active-sterile oscillations are suppressed. We show that a resonance energy in the range of 30–400 MeV allows an explanation of all neutrino oscillation data, including LSND data, in a consistent four-neutrino model. A high resonance energy implies an enhanced signal in MiniBooNE. A low resonance energy implies a distorted energy spectrum in LSND, and an enhanced ${\nu }_{\mu }$ depletion from a stopped-pion source. The numerical value of the resonance energy may be related back to the geometric aspects of the brane world. Some astrophysical and cosmological consequences of the brane-bulk resonance are briefly sketched.

We derive the overlap representation of chiral-odd generalized parton distributions using the Fock-state decomposition in the transverse-spin basis. This formalism is applied to the case of light-cone wave functions in a constituent quark model. Numerical results for the four chiral-odd generalized parton distributions at the hadronic scale are shown in different kinematics. In the forward limit we derive the transversity distribution, the tensor charge and the angular momentum sum rule for quarks with transverse polarization in an unpolarized nucleon.

The operator product expansion is used to obtain model-independent predictions for the first two moments of the renormalized $B$-meson light-cone distribution amplitude ${\varphi }_{+}^B(\omega ,\mu )$, defined with a cutoff $\omega \le {\Lambda }_{\mathrm{UV}}$. The leading hadronic power corrections are given in terms of the parameter $\overline{\Lambda }=m_B-m_b$. From the cutoff dependence of the zeroth moment an analytical expression for the asymptotic behavior of the distribution amplitude is derived, which exhibits a negative radiation tail for $\omega \gg \mu$. By solving the evolution equation for the distribution amplitude, an integral representation for ${\varphi }_{+}^B(\omega ,\mu )$ is obtained in terms an initial function ${\varphi }_{+}^B(\omega ,{\mu }_0)$ defined at a lower renormalization scale. A realistic model of the $B$-meson light-cone distribution amplitude is proposed, which satisfies the moment relations and has the correct asymptotic behavior. This model provides an estimate for the first inverse moment and the associated parameter ${\lambda }_B$.

We present a study of the $t$-channel mode of single top-quark production at the upgraded Tevatron $p\overline{p}$ collider, including the next-to-leading order quantum chromodynamics corrections to the production and the decay of a single top-quark. The narrow width approximation was adopted in order to preserve the spin of the top-quark in its production and decay. We discuss the effects of different $O({\alpha }_s)$ contributions on the inclusive cross section as well as various kinematic distributions after imposing the relevant cuts to select $t$-channel single top signal events.

By employing the QCD factorization approach, we calculate the new physics contributions to the branching radios of the two-body charmless $B\to PV$ and $B\to VV$ decays in the framework of the minimal supergravity (mSUGRA) model. We choose three typical sets of the mSUGRA input parameters in which the Wilson coefficient $C_{7\gamma }(m_b)$ can be either standard model (SM)-like (the case A and C) or has a flipped sign (the case B). We found numerically that (a) the SUSY contributions are always very small for both case A and C; (b) for those tree-dominated decays, the SUSY contributions in case B are also very small; (c) for those QCD penguin-dominated decay modes, the SUSY contributions in case B can be significant, and can provide an enhancement about $30\%\sim 260\%$ to the branching ratios of $B\to K^{*}(\pi ,\varphi ,\rho )$ and $K\varphi$ decays, but a reduction about $30\%\sim 80\%$ to $B\to K(\rho ,\omega )$ decays; and (d) the large SUSY contributions in the case B may be masked by the large theoretical errors dominated by the uncertainty from our ignorance of calculating the annihilation contributions in the QCD factorization approach.

We introduce an extension to the ladder truncated Bethe-Salpeter equation for mesons and the rainbow truncated quark Schwinger-Dyson equations which includes quark-loop corrections to the gluon propagator. This truncation scheme obeys the axialvector Ward-Takahashi identity relating the quark self-energy and the Bethe-Salpeter kernel. Two different approximations to the Yang-Mills sector are used as input: the first is a sophisticated truncation of the full Yang-Mills Schwinger-Dyson equations, the second is a phenomenologically motivated form. We find that the spectra and decay constants of pseudoscalar and vector mesons are overall described well for either approach. Meson mass results for charge eigenstate vector and pseudoscalar meson masses are compared to lattice data. The effects of unquenching the system are small but not negligible.

We perform a phenomenological analysis of dijet production in double Pomeron exchange at the Tevatron. We find that the CDF-Run I results do not rule out the presence of an exclusive dijet component, as predicted by Khoze, Martin and Ryskin (KMR). With the high-statistics CDF-Run II data, we predict that an exclusive component at the level predicted by KMR may be visible, although the observation will depend on accurate modeling of the inclusive double Pomeron exchange process. We also compare to the predictions of the DPEMC Monte Carlo, which contains a nonperturbative model for the central exclusive process. We show that the perturbative model of KMR gives different predictions for the dijet $E_T$ dependence in the high dijet mass fraction region than nonperturbative models.

The spin-singlet $P$-wave state of charmonium, $h_c{(}^1{P}_1)$, has been observed in the decay $\psi (2S)\to {\pi }^0{h}_c$ followed by $h_c\to \gamma {\eta }_c$. Inclusive and exclusive analyses of the $M(h_c)$ spectrum have been performed. Two complementary inclusive analyses select either a range of energies for the photon emitted in $h_c\to \gamma {\eta }_c$ or a range of values of $M({\eta }_c)$. These analyses, consistent with one another within statistics, yield $M(h_c)=[3524.9\pm 0.7(\mathrm{stat})\pm 0.4(\mathrm{sys})]\mathrm{MeV}/c^2$ and a product of the branching ratios ${\mathcal{B}}_{\psi }(\psi (2S)\to {\pi }^0{h}_c)\times {\mathcal{B}}_h(h_c\to \gamma {\eta }_c)=[3.5\pm 1.0(\mathrm{stat})\pm 0.7(\mathrm{sys})]\times {10}^{-4}$. When the ${\eta }_c$ is reconstructed in seven exclusive decay modes, $17.5\pm 4.5$ $h_c$ events are seen with an average mass $M(h_c)=[3523.6\pm 0.9(\mathrm{stat})\pm 0.5(\mathrm{sys})]\mathrm{MeV}/c^2$, and ${\mathcal{B}}_{\psi }{\mathcal{B}}_h=[5.3\pm 1.5(\mathrm{stat})\pm 1.0(\mathrm{sys})]\times {10}^{-4}$. If combined, the inclusive and exclusive data samples yield an overall mass $M(h_c)=[3524.4\pm 0.6(\mathrm{stat})\pm 0.4(\mathrm{sys})]\mathrm{MeV}/c^2$ and product of branching ratios ${\mathcal{B}}_{\psi }{\mathcal{B}}_h=[4.0\pm 0.8(\mathrm{stat})\pm 0.7(\mathrm{sys})]\times {10}^{-4}$. The $h_c$ mass implies a $P$-wave hyperfine splitting $\Delta M_{\mathrm{HF}}(1P)\equiv ⟨M(1^{3}P)⟩-M(1^1{P}_1)=[1.0\pm 0.6(\mathrm{stat})\pm 0.4(\mathrm{sys})]\mathrm{MeV}/c^2$.

In this paper we consider a simple generalization of the method of Lunin and Maldacena for generating new string backgrounds based on TsT transformations. We study multishift $Ts\cdots sT$ transformations applied to backgrounds with at least two U(1) isometries. We prove that the string currents in any two backgrounds related by $Ts\cdots sT$ transformations are equal. Applying this procedure to the $Ad{S}_5\times S^5$, we find a new background and study some properties of the semiclassical strings.

We revisit the general topic of thermodynamical stability and critical phenomena in black hole physics, analyzing in detail the phase diagram of the five dimensional rotating black hole and the black rings discovered by Emparan and Reall. First we address the issue of microcanonical stability of these spacetimes and its relation to thermodynamics by using the so-called Poincaré (or “turning point”) method, which we review in detail. We are able to prove that one of the black ring branches is always locally unstable, showing that there is a change of stability at the point where the two black ring branches meet. Next we study divergence of fluctuations, the geometry of the thermodynamic state space (Ruppeiner geometry) and compute the appropriate critical exponents and verify the scaling laws familiar from renormalization group theory in statistical mechanics. We find that, at extremality, the behavior of the system is formally very similar to a second order phase transition.

The Hamiltonian for a gravitating region includes a boundary term which determines not only the quasilocal values but also, via the boundary variation principle, the boundary conditions. Using our covariant Hamiltonian formalism, we found four particular quasilocal energy-momentum boundary term expressions; each corresponds to a physically distinct and geometrically clear boundary condition. Here, from a consideration of the asymptotics, we show how a fundamental Hamiltonian identity naturally leads to the associated quasilocal energy flux expressions. For electromagnetism one of the four is distinguished: the only one which is gauge invariant; it gives the familiar energy density and Poynting flux. For Einstein’s general relativity two different boundary condition choices correspond to quasilocal expressions which asymptotically give the ADM energy, the Trautman-Bondi energy and, moreover, an associated energy flux (both outgoing and incoming). Again there is a distinguished expression: the one which is covariant.

We demonstrate explicit counterexamples to the correlated stability conjecture (CSC), which claims that the horizon of a black brane is unstable precisely if that horizon has a thermodynamic instability, meaning that its matrix of susceptibilities has a negative eigenvalue. These examples involve phase transitions near the horizon. Ways to restrict or revise the CSC are suggested. One of our examples shows that $\mathcal{N}=1^{*}$ gauge theory has a second-order chiral symmetry breaking phase transition at a temperature well above the confinement scale.

We study the cosmological and weak-field properties of theories of gravity derived by extending general relativity by means of a Lagrangian proportional to $R^{1+\delta }$. This scale-free extension reduces to general relativity when $\delta \to 0$. In order to constrain generalizations of general relativity of this power class, we analyze the behavior of the perfect-fluid Friedmann universes and isolate the physically relevant models of zero curvature. A stable matter-dominated period of evolution requires $\delta >0$ or $\delta <-1/4$. The stable attractors of the evolution are found. By considering the synthesis of light elements (helium-4, deuterium and lithium-7) we obtain the bound $-0.017<\delta <0.0012$. We evaluate the effect on the power spectrum of clustering via the shift in the epoch of matter-radiation equality. The horizon size at matter-radiation equality will be shifted by $\sim 1\%$ for a value of $\delta \sim 0.0005$. We study the stable extensions of the Schwarzschild solution in these theories and calculate the timelike and null geodesics. No significant bounds arise from null geodesic effects but the perihelion precession observations lead to the strong bound $\delta =2.7\pm 4.5\times {10}^{-19}$ assuming that Mercury follows a timelike geodesic. The combination of these observational constraints leads to the overall bound $0\le \delta <7.2\times {10}^{-19}$ on theories of this type.

The conventional method using low energy theorems derived by Chanowitz et al. [Phys. Rev. Lett. 57, 2344 (1986);] does not seem to lead to an explicit unitarity limit in the scattering processes of longitudinally polarized gauge bosons for the high energy case in the extra $U(1)$ superstring inspired models, commonly known as $\eta$ model, emanating from $E_6$ group of superstring theory. We have made use of an alternative procedure given by Durand & Lopez [Phys. Lett. B 217, 463 (1989);], which is applicable to supersymmetric grand unified theories. Explicit unitarity bounds on the superpotential couplings (identified as Yukawa couplings) are obtained from both using unitarity constraints as well as using renormalization group equations (RGE) analysis at one-loop level utilizing critical couplings concepts implying divergence of scalar coupling at $M_G$. These are found to be consistent with finiteness over the entire range $M_Z\le \sqrt{s}\le M_G$ i.e. from grand unification scale to weak scale. For completeness, the similar approach has been made use of in other models i.e., $\chi$, $\psi$, and $\nu$ models emanating from $E_6$ and it has been noticed that at weak scale, the unitarity bounds on Yukawa couplings do not differ among $E_6$ extra $U(1)$ models significantly except for the case of χ model in $\mathbf{16}$ representations. For the case of the $E_6$-$\eta$ model $({\beta }_E\cong 9.64)$, the analysis using the unitarity constraints leads to the following bounds on various parameters: ${\lambda }_{t(\max .)}(M_Z)=1.294$, ${\lambda }_{b(\max .)}(M_Z)=1.278$, ${\lambda }_{H(\max .)}(M_Z)=0.955$, ${\lambda }_{D(\max .)}(M_Z)=1.312$. The analytical analysis of RGE at the one-loop level provides the following critical bounds on superpotential couplings: ${\lambda }_{t,c}(M_Z)\cong 1.295$, ${\lambda }_{b,c}(M_Z)\cong 1.279$, ${\lambda }_{H,c}(M_Z)\cong 0.968$, ${\lambda }_{D,c}(M_Z)\cong 1.315$. Thus superpotential coupling values obtained by both the approaches are in good agreement. Theoretically we have obtained bounds on physical mass parameters using the unitarity constrained superpotential couplings. The bounds are as follows: (i) Absolute upper bound on top quark mass $m_t\le 225\mathrm{GeV}$, (ii) the upper bound on the lightest neutral Higgs boson mass at the tree level is $m_{H_2^0}^{\mathrm{tree}}\le 169\mathrm{GeV}$, and after the inclusion of the one-loop radiative correction it is $m_{H_2^0}\le 229\mathrm{GeV}$ when ${\lambda }_t\ne {\lambda }_b$ at the grand unified theory scale. On the other hand, these are $m_{H_2^0}^{\mathrm{tree}}\le 159\mathrm{GeV}$, $m_{H_2^0}\le 222\mathrm{GeV}$, respectively, when ${\lambda }_t={\lambda }_b$ at the grand unified theory scale. A plausible range on $D$-quark mass as a function of mass scale $M_{Z_2}$ is $m_D\approx O(3\mathrm{TeV})$ for $M_{Z_2}\approx O(1\mathrm{TeV})$ for the favored values of $\tan \beta \le 1$. The bounds on aforesaid physical parameters in the case of $\chi$, $\psi$, and $\nu$ models in the $\mathbf{27}$ representation are almost identical with those of $\eta$ model and are consistent with the present day experimental precision measurements.

Little experimental data bears on the question of whether there is a spontaneously broken hidden sector that has no Standard Model quantum numbers. Here we discuss the prospects of finding evidence for such a hidden sector through renormalizable interactions of the Standard Model Higgs boson with a Higgs boson of the hidden sector. We find that the lightest Higgs boson in this scenario has smaller rates in standard detection channels, and it can have a sizeable invisible final state branching fraction. Details of the hidden sector determine whether the overall width of the lightest state is smaller or larger than the Standard Model width. We compute observable rates, total widths and invisible decay branching fractions within the general framework. We also introduce the “A-Higgs Model”, which corresponds to the limit of a hidden sector Higgs boson weakly mixing with the Standard Model Higgs boson. This model has only one free parameter in addition to the mass of the light Higgs state and it illustrates most of the generic phenomenology issues, thereby enabling it to be a good benchmark theory for collider searches. We end by presenting an analogous supersymmetry model with similar phenomenology, which involves hidden sector Higgs bosons interacting with MSSM Higgs bosons through D-terms.

We compute the spectrum of normalizable fermion bound states in a Schwarzschild black hole background. The eigenstates have complex energies. The real parts of the energies, for small couplings, closely follow a hydrogenlike spectrum. The imaginary parts give decay times for the various states, due to the absorption properties of the hole, with states closer to the hole having shorter half-lives. As the coupling increases, the spectrum departs from that of the hydrogen atom, as states close to the horizon become unfavorable. Beyond a certain coupling the $1S_{1/2}$ state is no longer the ground state, which shifts to the $2P_{3/2}$ state, and then to states of successively greater angular momentum. For each positive energy state a negative energy counterpart exists, with opposite sign of its real energy, and the same decay factor. It follows that the Dirac sea of negative energy states is decaying, which may provide a physical contribution to Hawking radiation.

I present the two-loop self-energy functions and pole masses for fermions in an arbitrary renormalizable field theory in the approximation that vector bosons are treated as massless. The calculations are done simultaneously in the mass-independent $\overline{\mathrm{MS}}$, $\overline{\mathrm{DR}}$, and ${\overline{\mathrm{DR}}}^{\prime }$ renormalization schemes, with a general covariant gauge fixing, and treating Majorana and Dirac fermions in a unified way. As examples, I discuss the two-loop strong interaction corrections to the gluino, neutralino, chargino, and quark pole masses in minimal supersymmetry. All other two-loop contributions to the fermion pole masses in softly broken supersymmetry also can be obtained as special cases of the results given here, neglecting only the electroweak symmetry breaking scale compared to larger mass scales in two-loop diagrams that involve $W$ or $Z$ bosons.

The possibility of color ferromagnetism in a $SU(2)$ gauge field model is investigated. The conditions allowing a stable color ferromagnetic state of the quark system in the chromomagnetic field occupying small domains are considered. A phase transition between this state and the color superconducting states is considered. The effect of finite temperature is analyzed.