The newly observed ${\Theta }^{+}$ resonance is believed to be a pentaquark with the constituent quarks $\mathrm{uudd}\overline{s}.$ There are a few options for the constituent quark structure. Some advocate diquark-diquark-antiquark $\mathrm{}\left(\mathrm{ud}\right)\mathrm{}-\mathrm{}\left(\mathrm{ud}\right)\mathrm{}-\overline{s}$ while others favor diquark-triquark $\mathrm{}\left(\mathrm{ud}\right)\mathrm{}-\left(ud\overline{s}\right)$ structure. We use the color-spin hyperfine interaction to examine the energy levels of these structures, and we find that the diquark-diquark-antiquark structure is slightly favored. We proceed to write down the flavor triplet and antisextet of the charmed or bottomed exotic baryons with internal $\mathrm{qqqq}\overline{Q}$ quarks. We also estimate the mass of ${\Theta }_c^0$ and ${\Theta }_b^{+}.$

Motivated by measurements of the flavor singlet axial coupling constant of the nucleon in polarized deep inelastic scattering we study the contribution of instantons to Okubo-Zweig-Iizuka rule (OZI) violation in the axial-vector channel. We consider, in particular, the $f_1-a_1$ meson splitting, the flavor singlet and triplet axial coupling of a constituent quark, and the axial coupling constant of the nucleon. We show that instantons provide a short distance contribution to OZI violating correlation functions which is repulsive in the $f_1$ meson channel and adds to the flavor singlet three-point function of a constituent quark. We also show that the sign of this contribution is determined by positivity arguments. We compute long distance contributions using numerical simulations of the instanton liquid. We find that the isovector axial coupling constant of a constituent quark is ${(g}_A^3{)}_Q=0.9\mathrm{}$ and that of a nucleon is $g_A^3=1.28,$ in good agreement with experiment. The flavor singlet coupling of a quark is close to one, while that of a nucleon is suppressed, $g_A^0=\mathrm{0.77.}\mathrm{}$ However, this number is larger than the experimental value $g_A^0=(0.28\mathrm{}-0.41).$

Motivated by the recent observation of double-charm quark pair production by the Belle Collaboration, we calculate the complete $O\left({\alpha }_s^2\right)$ inclusive production cross sections for ${\eta }_c,$ $J/\psi ,$ and ${\chi }_{\mathrm{cJ}}$ $\mathrm{}(J=0,1,2\mathrm{})\mathrm{}$ plus $c\overline{c}$ in $e^{+}{e}^{-}$ annihilation through a virtual photon. We consider both color-singlet and color-octet contributions, and give the analytical expressions for these cross sections. The complete color-singlet calculations are compared with the approximate fragmentation calculations as functions of the center-of-mass energy $\sqrt{s}.$ We find that most of the fragmentation results substantially overestimate the cross sections (e.g., by a factor of $\sim 4$ for ${\chi }_{c1\mathrm{}}$ and ${\chi }_{c2\mathrm{}})$ at the Belle and BaBar energy $\sqrt{s}=10.6\mathrm{}\mathrm{GeV}.$ The fragmentation results become a good approximation only when $\sqrt{s}$ is higher than about 100 GeV. We further calculate the color-octet contributions to these cross sections with analytical expressions. We find that while the color-octet contribution to $J/\psi$ inclusive production via double charm is negligible (only about 7%), the color-octet contributions to ${\chi }_{c1\mathrm{}}$ and ${\chi }_{c2\mathrm{}}$ can be very significant.

The large rate of the $J/\psi +{\eta }_c$ production observed by the Belle Collaboration has posed a serious challenge to our understanding of quarkonium. We examine a scenario in which there exists a light scalar boson around 5 GeV, with an enhanced coupling solely to the charm quark. Such a scenario would explain the Belle anomaly. It also predicts a significant increase in $J/\psi$ plus open charm pair production. An immediate test for the scalar boson is to look for a peak around 5 GeV in the recoil mass spectrum of $J/\psi ,$ because the scalar boson can also be produced in association with the $J/\psi .$ Finally, we also point out that the process $e^{+}{e}^{-}\to H\gamma$ is sizable for observation.

We propose that back-to-back correlations in the azimuthal angle of jets produced in collisions of unpolarized with transversely polarized proton beams could be used to determine Sivers functions. The corresponding single-spin asymmetry is not power suppressed, but is subject to Sudakov suppression. We present estimates of the asymmetry (without and with Sudakov effects) for BNL RHIC at jet transverse momenta of $\sim 10\mathrm{GeV}$ and show that it may reach a few percent or more and could provide access to the gluon Sivers function.

I attempt to quantify how far from maximal one should expect the atmospheric mixing angle to be given a neutrino mass matrix that leads, at zeroth order, to a ${\nu }_3$ mass eigenstate that is 0% ${\nu }_e,$ 50% ${\nu }_{\mu },$ and 50% ${\nu }_{\tau }.$ This is done by assuming that the solar mass-squared difference is induced by an “anarchical” first order perturbation, an approach then can naturally lead to experimentally allowed values for all oscillation parameters. In particular, both $|\cos 2{\theta }_{\mathrm{atm}}|$ (the measure for the deviation of atmospheric mixing from maximal) and $|U_{e3\mathrm{}}|$ are of order $\sqrt{\Delta m_{\mathrm{sol}}^2/\Delta m_{\mathrm{atm}}^2}$ in the case of a normal neutrino mass hierarchy or of order $\Delta m_{\mathrm{sol}}^2/\Delta m_{\mathrm{atm}}^2$ in the case of an inverted one. Hence, if any of the textures analyzed here has anything to do with reality, next-generation neutrino experiments can see a nonzero $\cos 2{\theta }_{\mathrm{atm}}$ in the case of a normal mass hierarchy, while in the case of an inverted mass hierarchy only neutrino factories should be able to see a deviation of ${\sin }^{2}2{\theta }_{\mathrm{atm}}$ from 1.

Recently Babu, Ma, and Valle proposed a model of quark and lepton mixing based on $A_4$ symmetry [Phys. Lett. B 552, 207 (2003)]. Within this model, the lepton and slepton mixings are intimately related. We perform a numerical study in order to derive the slepton masses and mixings in agreement with present data from neutrino physics. We show that, starting from threefold degeneracy of the neutrino masses at a high-energy scale, a viable low-energy neutrino mass matrix can indeed be obtained in agreement with constraints on lepton flavor violating $\mu$ and $\tau$ decays. The resulting slepton spectrum must necessarily include at least one mass below 200 GeV which can be produced at the CERN Large Hadron Collider. The prediction for the absolute Majorana neutrino mass scale $m_0>~0.3\mathrm{eV}$ ensure that the model will be tested by future cosmological tests and neutrinoless double beta decay searches. Rates for lepton flavor-violating processes ${\mathcal{l}}_j\to {\mathcal{l}}_i+\gamma$ in the range of sensitivity of current experiments are typical in the model, with $\mathrm{BR}\left(\overrightarrow{\mu }e\gamma \right)\gtrsim {10}^{-15}$ and the lower bound $\mathrm{BR}\left(\overrightarrow{\tau }\mu \gamma \right)>\mathrm{}{10}^{-9}.$ To first approximation, the model leads to maximal leptonic CP violation in neutrino oscillations.

Recent precise measurements of $\sin 2\beta$ from the B factories (BABAR and BELLE) and a better known strange quark mass from lattice QCD make precision tests of predictive texture models possible. The models tested include those hierarchical N-zero textures classified by Ramond, Roberts, and Ross, as well as any other hierarchical matrix Ansätze with nonzero $12=21$ and vanishing 11 and 13 elements. We calculate the maximally allowed value for $\sin 2\beta$ in these models and show that all the aforementioned models with vanishing 11 and 13 elements are ruled out at the $3\sigma$ level. While at present $\sin 2\beta$ and $|V_{\mathrm{ub}}{/V}_{\mathrm{cb}}|$ are equally good for testing N-zero texture models, in the near future the former will surpass the latter in constraining power.

Motivated by the work of Gen and Sasaki, we examine whether the matching of the false vacuum instanton with the Coleman–De Luccia bounce is operator-ordering independent.

In this paper, we study the phase space of a phantom model with $\mathrm{O}\mathrm{}\left(N\right)\mathrm{}$ symmetry in an exponential potential. Different from the model without O(N) symmetry, the introduction of the symmetry leads to a lower bound $w>\mathrm{}-3$ on the equation of state for the existence of a stable phantom dominated attractor phase. The reconstruction relation between the potential of the $\mathrm{O}\mathrm{}\left(N\right)\mathrm{}$ phantom system and redshift has been derived.

In this paper we consider a strong-weak coupling duality of the $N=2\mathrm{}$ super-Liouville field theory (SLFT). Without the self-duality found in other Liouville theories, the $N=2\mathrm{}$ SLFT, we claim, is associated with a “dual” action by a transformation $\overrightarrow{b}1/b$ where b is the coupling constant. To justify our conjecture, we compute the reflection amplitudes (or two-point functions) of the Neveu-Schwarz and Ramond operators of the $N=2\mathrm{}$ SLFT based on the conjectured dual action and show that the results are consistent with known results.

We examine giant gravitons with a world volume magnetic flux q in a type IIA pp-wave background and find that they can move away from the origin along the $x^4$ direction in target space satisfying ${\mathrm{Rx}}^4=-q.\mathrm{}$ This nontrivial relation can be regarded as a complementary relation of the giant graviton on a type IIA pp wave and is shown to be connected to the spacetime uncertainty principle. The giant graviton is also investigated in a system of N D0-branes as a fuzzy sphere solution. It is observed that $x^4$ enters into the fuzzy algebra as a deformation parameter. Such a background-dependent Myers effect guarantees that again we get the crucial relation of our giant graviton. In the paper, we also find a BIon configuration on the giant graviton in this background.

In a previous paper [Nucl. Phys. B666, 56 (2003)] it was argued that tachyonic Dirac-Born-Infeld (DBI) actions can be obtained from open string theory in a limit, which generalizes the usual massless DBI limit. In the present paper we review this construction, focusing on a key property of the proposed tachyon effective actions: how they reproduce appropriate Veneziano amplitudes in a suitably defined kinematical region. Possible extensions and interesting open problems are briefly discussed.

We investigate the stability of inflating branes embedded in an O(2) texture formed in one extra dimension. The model contains two 3-branes of nonzero tension, and the extra dimension is compact. When the gravitational perturbation is applied, the vacuum energy which is responsible for inflation on the branes stabilizes the branes if the symmetry-breaking scale of the texture is smaller than some critical value. This critical value is determined by the particle-hierarchy scale between the two branes, and is smaller than the 5D Planck-mass scale. The scale of the vacuum energy can be considerably low in providing the stability. This stability story is very different from the flat-brane case which always suffers from the instability due to the gravitational perturbation.

We derive a kinetic equation with a non-Markovian collision term that includes a memory effect from Kadanoff-Baym equations in ${\phi }^4$ theory within the three-loop level for the two-particle irreducible effective action. The memory effect is incorporated into the kinetic equation by a generalized Kadanoff-Baym ansatz. Based on the kinetic equations with and without the memory effect, we investigate the influence of this effect on the decay of a single particle excitation with zero momentum in 3+1 dimensions and the spatially homogeneous case. The numerical results show that, while the time evolution of the zero mode is completely unaffected by the memory effect due to a separation of scales in the weak coupling regime, this effect leads first to faster relaxation than the case without it and then to slower relaxation as the coupling constant increases.

Perfect fluid spheres, either Newtonian or relativistic, are the first step in developing realistic stellar models (or models for fluid planets). Despite the importance of these models, explicit and fully general solutions of the perfect fluid constraint in general relativity have only very recently been developed. In this paper we present a variant of Lake’s algorithm wherein (1) we recast the algorithm in terms of variables with a clear physical meaning—the average density and the locally measured acceleration due to gravity, (2) we present explicit and fully general formulas for the mass profile and pressure profile, and (3) we present an explicit closed-form expression for the central pressure. Furthermore we can then use the formalism to easily understand the pattern of interrelationships among many of the previously known exact solutions, and generate several new exact solutions.

We review the generalized Witten-Nester spinor stability argument for flat domain wall solutions of gravitational theories. Neither the field theory nor the solution need be supersymmetric. Nor is the space-time dimension restricted. We develop the nontrivial extension required for AdS-sliced domain walls and apply this to show that the recently proposed “Janus” solution of type-IIB supergravity is stable nonperturbatively for a broad class of deformations. Generalizations of this solution to arbitrary dimension and a simple curious linear dilaton solution of type-IIB supergravity are by-products of this work.

Core collapse in massive stars is believed to produce a rapidly spinning black hole surrounded by a compact disk or torus. This forms an energetic MeV nucleus inside a remnant He core, powered by black-hole–spin energy. The output produces a GRB supernova, while most of the energy released is in gravitational radiation. The intrinsic gravitational-wave spectrum is determined by multipole mass moments in the torus. Here we discuss line broadening in the observed spectrum due to Lense-Thirring precession, which modulates the orientation of the torus to the line of sight. This spectral feature is long lived, due to weak damping of precessional motion. These events are believed to occur perhaps once per year within a distance of 100 Mpc, which provides a candidate source for advanced LIGO.

A variety of observations indicate that the Universe is dominated by “dark energy” with negative pressure, one possibility for which is a cosmological constant. If the dark energy is a cosmological constant, a fundamental question is, why has it become relevant at so late an epoch, making today the only time in the history of the Universe at which the cosmological constant is of the order of the ambient density. We explore an answer to this question drawing on ideas from unimodular gravity, which entails fluctuations in the cosmological constant, and causal set theory, which predicts a specific magnitude for the fluctuations. The resulting ansatz provides a cosmological “constant” which fluctuates about zero, remaining always comparable to the ambient energy density.

We reexamine leptogenesis from a right-handed sneutrino condensate, paying special attention to the B term associated with the seesaw Majorana mass. This term generates a lepton asymmetry in the condensate whose time average vanishes. However, a net asymmetry will result if the sneutrino lifetime is not much longer than the period of oscillations. Supersymmetry breaking by thermal effects then yields a lepton asymmetry in the standard model sector after the condensate decays. We explore different possibilities by taking account of both the low-energy and Hubble B terms. It will be shown that the desired baryon asymmetry of the Universe can be obtained for a wide range of Majorana masses.