We address the question of the Lorentz nature of the effective interquark interaction in QCD which leads to the formation of the QCD string between color charges. In particular, we start from a manifestly vectorial fundamental interaction mediated by gluons and demonstrate that, as soon as chiral symmetry is broken spontaneously, the effective interquark interaction acquires a self-consistently generated scalar part which is eventually responsible for the formation of the QCD string. We demonstrate this explicitly for a heavy-light quarkonium, using the approach of the Schwinger-Dyson-type equation and the quantum-mechanical Hamiltonian method of the QCD string with quarks at the ends.

To understand the whole set of positive and null data on the ${\Theta }^{+}(1530)$-production, we suggest the hypothesis that multiquark hadrons are mainly generated from many-quark states, which emerge either as short-term hadron fluctuations, or as hadron remnants in hard processes. This approach allows us to describe both nonobservation of the ${\Theta }^{+}$ in current null experiments and peculiar features of its production in positive experiments. Further, we are able to propose new experiments that might be decisive for the problem of the ${\Theta }^{+}$ existence. Studies of properties and distributions of the ${\Theta }^{+}$ in such experiments can give important information on the structure of both conventional and multiquark hadrons. It would provide better insight into how QCD works.

We study the $e^{+}{e}^{-}\to \varphi \pi \pi$ reaction for pions in an isoscalar $s$ wave which is dominated by loop mechanisms. For kaon loops we start from the conventional $R\chi PT$, but use the unitarized amplitude for $K\overline{K}-\pi \pi$ scattering and the full kaon form factor instead of the lowest order terms. We study also effects of vector mesons using $R\chi PT$ supplemented with the conventional anomalous term for $VVP$ interactions and taking into account the effects of heavy vector mesons in the $K^{*}K$ transition form factor. We find a peak in $m_{\pi \pi }$ around the $f_0(980)$ as in the experiment. Selecting the $\varphi f_0(980)$ contribution as a function of the $e^{+}{e}^{-}$ energy we also reproduce the experimental data except for a narrow peak, yielding support to the existence of a $1^{--}$ resonance above the $\varphi f_0(980)$ threshold, coupling strongly to this state.

The meson-cloud model of the nucleon consisting of a system of three valence quarks surrounded by a meson cloud is applied to study the electroweak structure of the proton and neutron. Light-cone wave functions are derived for the dressed nucleon as pictured to be part of the time a bare nucleon and part of the time a baryon-meson system. Configurations are considered where the baryon can be a nucleon or a $\Delta$ and the meson can be a pion as well as a vector meson such as the $\rho$ or the $\omega$. An overall good description of the electroweak form factors is obtained. The contribution of the meson cloud is small and only significant at low $Q^2$. Mixed-symmetry $S^{\prime }$-wave components in the wave function are most important to reproduce the neutron electric form factor. Charge and magnetization densities are deduced as a function of both the radial distance from the nucleon center and the transverse distance with respect to the direction of the three-momentum transfer. In the latter case, a central negative charge is found for the neutron. The up and down quark distributions associated with the Fourier transform of the axial form factor have opposite sign, with the consequence that the probability to find an up (down) quark with positive helicity is maximal when it is (anti)aligned with the proton helicity.

We examine the soft-gluon resummation effects, including the exact spin correlations among the final state particles, in the search of the standard model Higgs boson, via the process $gg\to H\to WW/ZZ\to 4$ leptons, at the Tevatron and the LHC. A comparison between the resummation and the next-to-leading order (NLO) calculation is performed after imposing various kinematics cuts suggested in the literature for the Higgs boson search. For the $H\to ZZ$ mode, the resummation effects increase the acceptance of the signal events by about 25%, as compared to the NLO prediction, and dramatically alter various kinematics distributions of the final state leptons. For the $H\to WW$ mode, the acceptance rates of the signal events predicted by the resummation and NLO calculations are almost the same, but some of the predicted kinematical distributions are quite different. Thus, to precisely determine the properties of the Higgs boson at hadron colliders, the soft-gluon resummation effects have to be taken into account.

The velocity of a $\sim 3\mathrm{GeV}$ neutrino beam is measured by comparing detection times at the near and far detectors of the MINOS experiment, separated by 734 km. A total of 473 far detector neutrino events was used to measure $(v-c)/c=5.1\pm 2.9\times {10}^{-5}$ (at 68% C.L.). By correlating the measured energies of 258 charged-current neutrino events to their arrival times at the far detector, a limit is imposed on the neutrino mass of $m_{\nu }<50\mathrm{MeV}/c^2$ (99% C.L.).

We present a measurement of the branching fraction and time-dependent $CP$ violation parameters for $B^0\to D^{*+}{D}^{*-}{K}_S^0$ decays. These results are obtained from a $414{\mathrm{fb}}^{-1}$ data sample that contains $449\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We obtain the branching fraction, $\mathcal{B}(B^0\to D^{*+}{D}^{*-}{K}_S^0)=[3.4\pm 0.4(\mathrm{stat})\pm 0.7(\mathrm{syst})]\times {10}^{-3}$, which is in agreement with the current world average. We also obtain an upper limit on the product branching fraction for a possible two-body decay, $\mathcal{B}(B^0\to D_{\mathrm{s}1}^{+}(2536)D^{*-})\mathcal{B}(D_{\mathrm{s}1}^{+}(2536)\to D^{*+}{K}_S^0)<7.1\times {10}^{-4}$ (90% CL). In the traditional 2-parameter time-dependent $CP$ analysis, we measure the $CP$ violation parameters, ${\mathcal{A}}_{CP}=-{0.01}_{-0.28}^{+0.28}(\mathrm{stat})\pm 0.09(\mathrm{syst})$, $D\sin 2{\varphi }_1={0.06}_{-0.44}^{+0.45}(\mathrm{stat})\pm 0.06(\mathrm{syst})$. No evidence for either mixing-induced or direct $CP$ violation is found. In a 3-parameter fit sensitive to $\cos 2{\varphi }_1$ performed in the half-Dalitz spaces, $s^{-}\le s^{+}$ and $s^{-}>s^{+}$, where $s^{\pm }\equiv m^2(D^{*\pm }{K}_S^0)$, we extract the $CP$ violation parameters, $J_{\mathrm{c}}/J_0={0.60}_{-0.28}^{+0.25}(\mathrm{stat})\pm 0.08(\mathrm{syst})$, $2J_{\mathrm{s}1}/J_0\sin 2{\varphi }_1=-{0.17}_{-0.42}^{+0.42}(\mathrm{stat})\pm 0.09(\mathrm{syst})$, $2J_{\mathrm{s}2}/J_0\cos 2{\varphi }_1=-{0.23}_{-0.41}^{+0.43}(\mathrm{stat})\pm 0.13(\mathrm{syst})$. A large value of $J_{\mathrm{c}}/J_0$ would indicate a significant resonant contribution from a broad unknown $D_{\mathrm{s}}^{**+}$ state. Although the sign of the factor, $2J_{\mathrm{s}2}/J_0$, can be deduced from theory, no conclusion can be drawn regarding the sign of $\cos 2{\varphi }_1$ given the errors.

The divergence of the axial current is used to relate the spatial derivative of the fermion density to the bare fermion mass and scalar/pseudoscalar condensates in $1+1$ dimensional Gross-Neveu models. This serves as a useful test of known results, to explain simple features of the continuous chiral model and to resolve a conflict concerning the assignment of baryon number to certain multifermion bound states.

In this work we study modifications in the Aharonov-Bohm effect for relativistic spin $1/2$ particles due to the noncommutativity of spacetime in $2+1$ dimensions. The noncommutativity gives rise to a correction to the Aharonov-Bohm potential which is highly singular at the origin, producing divergences in a perturbative expansion around the usual solution of the free Dirac equation. This problem is surmounted by using a perturbative expansion around the exact solution of the commutative Aharonov-Bohm problem. We calculate, in this setting, the scattering amplitude and the corrections to the differential and total cross sections for a spin $1/2$ particle, in the small-flux limit.

Two families of exact general relativistic rotating thick disks based on the Kerr metric are obtained by applying two kinds of transformation on the Kerr solution. The first is the one proposed by Miyamoto and Nagai in the context of Newtonian galactic models, and the second one is based on the “displace, cut, fill and reflect” method. Both kinds of disks have well-behaved energy-density distributions. A stability analysis of circular orbits on the $z=0$ plane shows that for large values of the Kerr parameter some retrograde orbits tend to be unstable.

The phenomenology of quantum systems in curved space-times is among the most fascinating fields of physics, allowing—often at the gedankenexperiment level—constraints on tentative theories of quantum gravity. Determining the dynamics of fields in curved backgrounds remains, however, a complicated task because of the highly intricate partial differential equations involved, especially when the space metric exhibits no symmetry. In this article, we provide—in a pedagogical way—a general formalism to determine this dynamics at the semiclassical order. To this purpose, a generic expression for the semiclassical propagator is computed and the equation of motion for the probability four-current is derived. Those results underline a direct analogy between the computation of the propagator in general relativistic quantum mechanics and the computation of the propagator for stationary systems in nonrelativistic quantum mechanics. A possible application of this formalism to curvature-induced quantum interferences is also discussed.

In a quantum theory of gravity the gravitational Wilson loop, defined as a suitable quantum average of a parallel transport operator around a large near-planar loop, provides important information about the large-scale curvature properties of the geometry. Here we shows that such properties can be systematically computed in the strong coupling limit of lattice regularized quantum gravity, by performing local averages over loop bivectors, and over lattice rotations, using an assumed near-uniform measure in group space. We then relate the resulting quantum averages to an expected semiclassical form valid for macroscopic observers, which leads to an identification of the gravitational correlation length appearing in the Wilson loop with an observed large-scale curvature. Our results suggest that strongly coupled gravity leads to a positively curved (de Sitter-like) quantum ground state, implying a positive effective cosmological constant at large distances.

We formulate and calculate the second-order quasinormal modes (QNMs) of a Schwarzschild black hole (BH). Gravitational waves (GW) from a distorted BH, the so-called ringdowns, are well understood as QNMs in general relativity. Since QNMs from binary BH mergers will be detected with a high signal-to-noise ratio by GW detectors, it is also possible to detect the second perturbative order of QNMs, generated by nonlinear gravitational interaction near the BH. In the BH perturbation approach, we derive the master Zerilli equation for the metric perturbation to second order and explicitly regularize it at the horizon and spatial infinity. We numerically solve the second-order Zerilli equation by implementing the modified Leaver continued fraction method. The second-order QNM frequencies are found to be twice the first-order ones, and the GW amplitude is up to $\sim 10\%$ that of the first order for the binary BH mergers. Since the second-order QNMs always exist, we can use their detections (i) to test the nonlinearity of general relativity, in particular, the no-hair theorem, (ii) to remove fake events in the data analysis of QNM GWs, and (iii) to measure the distance to the BH.

We discuss inflaton decay in supergravity, taking account of the gravitational effects. It is shown that, if the inflaton has a nonzero vacuum expectation value, it generically couples to any matter fields that appear in the superpotential at the tree level, and to any gauge sectors through anomalies in the supergravity. Through these processes, the inflaton generically decays into the supersymmetry breaking sector, producing many gravitinos. The inflaton also directly decays into a pair of the gravitinos. We derive constraints on both inflation models and supersymmetry breaking scenarios for avoiding overproduction of the gravitinos. Furthermore, the inflaton naturally decays into the visible sector via the top Yukawa coupling and $\mathrm{SU}(3{)}_C$ gauge interactions.

We estimate the maximum equatorial ellipticity sustainable by compact stars composed of crystalline color-superconducting quark matter. For the theoretically allowed range of the gap parameter $\Delta$, the maximum ellipticity could be as large as ${10}^{-2}$, which is about 4 orders of magnitude larger than the tightest upper limit obtained by the recent science runs of the LIGO and GEO600 gravitational-wave detectors based on the data from 78 radio pulsars. We point out that the current gravitational-wave strain upper limit already has some implications for the gap parameter. In particular, the upper limit for the Crab pulsar implies that $\Delta$ is less than $O(20)\mathrm{MeV}$ for a range of quark chemical potential accessible in compact stars, assuming that the pulsar has a mass $1.4M_{\odot }$, radius 10 km, breaking strain ${10}^{-3}$, and that it has the maximum quadrupole deformation it can sustain without fracturing.

The existence of certain TeV suppressed higher-dimension operators may open up new decay channels for the Higgs boson to decay into lighter right-handed neutrinos. These channels may dominate over all other channels if the Higgs boson is light. For a Higgs boson mass larger than $2m_W$, the new decays are subdominant yet still of interest. The right-handed neutrinos have macroscopic decay lengths and decay mostly into final states containing leptons and quarks. A distinguishing collider signature of this scenario is a pair of displaced vertices violating lepton number. A general operator analysis is performed using the minimal flavor violation hypothesis to illustrate that these novel decay processes can occur while remaining consistent with experimental constraints on lepton number violating processes. In this context, the question of whether these new decay modes dominate is found to depend crucially on the approximate flavor symmetries of the right-handed neutrinos.

Motivated by recent experimental results on charm physics, we investigate implications of the updated constraints of new physics in rare charm meson decays. We first reconsider effects of the minimal supersymmetric standard model (MSSM) in $c\to u\gamma$ constrained by the recent experimental evidence on $\Delta m_D$ and find that, due to the dominance of long-distance physics, $D\to V\gamma$ decay rates cannot be modified by MSSM contributions. Then we consider effects of the extra heavy up vectorlike quark models on the decay spectrum of $D^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$ and $D_s^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays. We find a possibility for the tiny increase of the differential decay rate in the region of large dilepton mass. The $R$-parity violating supersymmetric model can also modify short distance dynamics in $c\to u{\ell }^{+}{\ell }^{-}$ decays. We constrain relevant parameters using the current upper bound on the $D^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$ decay rate and investigate the impact of that constraint on the $D_s^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ differential decay dilepton distribution. Present bounds still allow a small modification of the standard model differential decay rate distribution.

We consider the possibility to detect right-handed neutrinos, which are mostly singlets of the standard model gauge group, at future accelerators. Substantial mixing of these neutrinos with the active neutrinos requires a cancellation of different contributions to the light neutrino mass matrix at the level of ${10}^{-8}$. We discuss possible symmetries behind this cancellation and argue that for three right-handed neutrinos they always lead to conservation of total lepton number. Light neutrino masses can be generated by small perturbations violating these symmetries. In the most general case, LHC physics and the mechanism of neutrino mass generation are essentially decoupled; with additional assumptions, correlations can appear between collider observables and features of the neutrino mass matrix.

We estimate the isospin breaking contributions to the baryon masses which we analyzed recently using a loop expansion in the heavy-baryon chiral effective field theory. To one loop, the isospin breaking corrections come from the effects of the $d$, $u$ quark mass difference, the Coulomb and magnetic moment interactions, and effective point interactions attributable to color-magnetic effects. The addition of the first meson loop corrections introduces new structure. We estimate the resulting low-energy, long-range contributions to the mass splittings by regularizing the loop integrals using connections to dynamical models for finite-size baryons. We find that the resulting contributions to the isospin breaking corrections are of the right general size, have the correct sign pattern, and agree with the experimental values within the margin of error.

Recently we have proposed a renormalizable grand unified theory, based on the $SU(5)$ gauge symmetry, where the neutrino masses are generated through the type I and type III seesaw mechanisms. In this article we study the supersymmetric version of this theory. As in the nonsupersymmetric version it is possible to generate all fermion masses with the minimal number of Higgses, the theory predicts one massless neutrino, and the leptogenesis mechanism can be realized. All contributions to the decay of the proton and the properties of neutralinos are discussed. This theory can be considered as the simplest renormalizable supersymmetric grand unified theory based on the $SU(5)$ gauge symmetry since it has the minimal number of superfields and free parameters.