We calculate the spectrum of excitations in strong-coupling lattice QCD in a background of fixed baryon density, at a substantial fraction of the saturation density. We employ a next-nearest-neighbor fermion formulation that possesses the $SU(N_f)\times SU(N_f)$ chiral symmetry of the continuum theory. We find two types of massless excitations: type I Goldstone bosons with linear dispersion relations and type II Goldstone bosons with quadratic dispersion relations. Some of the type I bosons originate as type II bosons of the nearest-neighbor theory. Bosons of either type can develop anisotropic dispersion relations, depending on the value of $N_f$ and the baryon density.

We study the anomalous dimensions of single trace operators composed of field strengths $F_{\mu \nu }$ in large-$N$ QCD. The matrix of anomalous dimensions is the Hamiltonian of a compact spin chain with two spin one representations at each vertex corresponding to the self-dual and anti-self-dual components of $F_{\mu \nu }$. Because of the special form of the interaction it is possible to study separately renormalization of purely self-dual components. In this sector the Hamiltonian is integrable and can be exactly solved by Bethe ansatz. Its continuum limit is described by the level two SU(2) Wess-Zumino-Witten model.

A model recently introduced by Jaffe and Wilczek based on the quarks being dynamically bound into diquarks has been used to predict that the recently observed exotic baryons (pentaquarks) fall into a nearly ideally mixed combination of the 8 and $\overline{10}$ representations of $\mathrm{S}\mathrm{U}(3)$ flavor. The model predicts two states with nucleon quantum numbers which have tentatively been identified with the ${\mathrm{N}}^{*}(1440)$ and the ${\mathrm{N}}^{*}(1710)$. This paper examines the viability of this model by focusing on the decay width of the nucleon members of the multiplet. An inequality relating the partial widths of these nucleon states in the $\pi +\mathrm{\text{nucleon}}$ channel to the width of the ${\theta }^{+}$ is derived for this model assuming ideal mixing and that the only significant exact $\mathrm{S}\mathrm{U}(3)$ symmetry violations are the result of ideal mixing, threshold effects, and the masses of pseudo-Goldstone bosons. This inequality is badly violated if the states in the multiplet are the ${\mathrm{N}}^{*}(1440)$ and the ${\mathrm{N}}^{*}(1710)$ and if the recent bounds extracted for the ${\theta }^{+}$ width are reliable. Thus, the model appears to require a scenario with the existence of at least one presently unknown resonance with nucleon quantum numbers.

We present a measurement of the isolated direct photon cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{T}\mathrm{e}\mathrm{V}$ and $|\eta |<0.9$ using data collected between 1994 and 1995 by the Collider Detector at Fermilab (CDF). The measurement is based on events where the photon converts into an electron-positron pair in the material of the inner detector, resulting in a two track event signature. To remove ${\pi }^0\to \gamma \gamma$ and $\eta \to \gamma \gamma$ events from the data we use a new background subtraction technique which takes advantage of the tracking information available in a photon conversion event. We find that the shape of the cross section as a function of photon $p_T$ is poorly described by next-to-leading-order QCD predictions, but agrees with previous CDF measurements.

The existence of maximal and minimal mixing angles in the neutrino mixing matrix motivates the search for extensions to the standard model that may explain these angles. A previous study [C. I. Low and R. R. Volkas, Phys. Rev. D 68,, 033007 (2003)], began a systematic search to find the minimal extension to the standard model that explains these mixing angles. It was found that in the minimal extensions to the standard model which allow neutrino oscillations, discrete unbroken lepton family symmetries only generate neutrino mixing matrices that are ruled out by experiment. This paper continues the search by investigating all models with two or more Higgs doublets and an Abelian family symmetry. It is found that discrete Abelian family symmetries permit, but cannot explain, maximal atmospheric mixing; however, these models can ensure ${\theta }_{13}=0$.

Restricting the states of a charged particle to the lowest Landau level introduces a noncommutativity between Cartesian coordinate operators. This idea is extended to the motion of a charged particle on a sphere in the presence of a magnetic monopole. Restricting the dynamics to the lowest energy level results in noncommutativity for angular variables and to a definition of a noncommuting spherical product. The values of the commutators of various angular variables are not arbitrary but are restricted by the discrete magnitude of the magnetic monopole charge. An algebra, isomorphic to angular momentum, appears. This algebra is used to define a spherical star product. Solutions are obtained for dynamics in the presence of additional angular dependent potentials.

We use semiclassical methods to study closed strings in the modified $Ad{S}_5\times S^5$ background with constant $B$ fields. The pointlike closed strings and the stretched closed strings rotating around the big circle of $S^5$ are considered. Quantization of these closed string leads to a time-dependent string spectrum, which we argue corresponds to the renormalization-group flow of the dual noncommutative Yang-Mills theory.

I describe the Einstein’s gravitation of $3+1$ dimensional spacetimes using the (2,2) formalism without assuming isometries. In this formalism, quasilocal energy, linear momentum, and angular momentum are identified from the four Einstein’s equations of the divergence-type, and are expressed geometrically in terms of the area of a two-surface and a pair of null vector fields on that surface. The associated quasilocal balance equations are spelled out, and the corresponding fluxes are found to assume the canonical form of energy-momentum-flux as in standard field theories. The remaining non-divergence-type Einstein’s equations turn out to be the Hamilton’s equations of motion, which are derivable from the nonvanishing Hamiltonian by the variational principle. The Hamilton’s equations are the evolution equations along the out-going null geodesic whose affine parameter serves as the time function. In the asymptotic region of asymptotically flat spacetimes, it is shown that the quasilocal quantities reduce to the Bondi energy, linear momentum, and angular momentum, and the corresponding fluxes become the Bondi fluxes. The quasilocal angular momentum turns out to be zero for any two-surface in the flat Minkowski spacetime. I also present a candidate for quasilocal rotational energy which agrees with the Carter’s constant in the asymptotic region of the Kerr spacetime. Finally, a simple relation between energy-flux and angular momentum-flux of a generic gravitational radiation is discussed, whose existence reflects the fact that energy-flux always accompanies angular momentum-flux unless the flux is an $s$-wave.

It is known that the formation of apparent horizons with nonspherical topology is possible in higher-dimensional spacetimes. One of these is the black ring horizon with $S^1\times S^{D-3}$ topology where $D$ is the spacetime dimension number. In this paper, we investigate the black ring horizon formation in systems with $n$-particles. We analyze two kinds of system: the high-energy $n$-particle system and the momentarily-static $n$-black hole initial data. In the high-energy particle system, we prove that the black ring horizon does not exist at the instant of collision for any $n$. But there remains a possibility that the black ring forms after the collision and this result is not sufficient. Because calculating the metric of this system after the collision is difficult, we consider the momentarily-static $n$-black hole initial data that can be regarded as a simplified $n$-particle model and numerically solve the black ring horizon that surrounds all the particles. Our results show that there is the minimum particle number that is necessary for the black ring formation and this number depends on $D$. Although many particle number is required in five-dimensions, $n=4$ is sufficient for the black ring formation in the $D\ge 7$ cases. The black ring formation becomes easier for larger $D$. We provide a plausible physical interpretation of our results and discuss the validity of Ida and Nakao’s conjecture for the horizon formation in higher-dimensions. Finally we briefly discuss the probable methods of producing the black rings in accelerators.

We study the effects of shear and density inhomogeneities in the formation of naked singularities in spherically symmetric dust space-times. We find that in general, complete knowledge of either one of these (time-dependent) functions, along with physically motivated boundary conditions, fully determines the entire space-time and consequently uniquely specifies the end-state of the gravitational collapse. In contrast–and of more physical relevance–we show that measurements of shear or density inhomogenity at an instant of time do not uniquely determine the outcome of the collapse. We do this by (i) showing that, for open sets of initial data, the same initial shear (or initial density contrast) can give rise to both naked and covered solutions, in particular, this can happen for zero initial shear or zero initial density contrast; (ii)  demonstrating that asymptotically (near the singularity) both shear and density contrast are invariant under a one parameter set of linear transformations acting on the initial data set; and (iii) showing that asymptotically one cannot in general establish a direct relationship between the rate of change of shear (or density contrast) and the nature of the singularities. However, one can uniquely determine the nature of the singularity if both the initial shear and initial density contrast are known. These results are important in understanding the effects of the initial physical state and, in particular, the role of shear in determining the end-state of the gravitational collapse.

If the inflationary paradigm is correct, then it must create conditions for the hot big bang model with all observed matter, baryons, and the seed perturbations for structure formation. In this paper we propose a scenario where the inflaton energy density is dumped into the bulk in a brane world setup, and all the required physical conditions are created by the right-handed neutrino sector within supersymmetry. The scalar component of the right-handed Majorana neutrino is responsible for generating the scale invariant fluctuations in the cosmic microwave background radiation, reheating the Universe at a temperature $T_{\mathrm{r}\mathrm{h}}\le {10}^9\mathrm{G}\mathrm{e}\mathrm{V}$ and finally generating the lepton/baryon asymmetry $n_B/s\sim {10}^{-10}$ with no lepton/baryon-isocurvature fluctuations.

Cryptons are metastable bound states of fractionally-charged particles that arise generically in the hidden sectors of models derived from heterotic string. We study their properties and decay modes in a specific flipped SU(5) model with long-lived four-particle spin-zero bound states called tetrons. We show that the neutral tetrons are metastable, and exhibit the tenth order nonrenormalizable superpotential operators responsible for their dominant decays. By analogy with QCD, we expect charged tetrons to be somewhat heavier, and to decay relatively rapidly via lower-order interactions that we also exhibit. The expected masses and lifetimes of the neutral tetrons make them good candidates for cold dark matter, and a potential source of the ultrahigh energy cosmic rays which have been observed, whereas the charged tetrons would have decayed in the early Universe.

We calculate the tree-level oblique corrections to electroweak precision observables generated in Higgless models of electroweak symmetry breaking with a 5D $\mathrm{S}\mathrm{U}(2{)}_L\times \mathrm{S}\mathrm{U}(2{)}_R\times \mathrm{U}(1{)}_{B-L}$ gauge group on a warped background. In the absence of brane induced kinetic terms (and equal left and right gauge couplings) we find the $S$ parameter to be $\sim 1.15$, while $T\sim U\sim 0$, as in technicolor theories. Planck brane induced kinetic terms and unequal left-right couplings can lower $S$, however for sufficiently low values of $S$ tree-level unitarity will be lost. A kinetic term localized on the TeV brane for $\mathrm{S}\mathrm{U}(2{)}_D$ will generically increase $S$, however an induced kinetic term for $\mathrm{U}(1{)}_{B-L}$ on the TeV brane will lower $S$. With an appropriate choice of the value of this induced kinetic term $S\sim 0$ can be achieved. In this case the mass of the lowest $Z^{\prime }$ mode will be lowered to about 300 GeV.

We investigate the confining properties of the QCD vacuum with $N_f=2$ flavors of dynamical quarks, and compare the results with the properties of the quenched theory. We use nonperturbatively $\mathcal{O}(a)$ improved Wilson fermions to keep cutoff effects small. We focus on color magnetic monopoles. Among the quantities we study are the monopole density and the monopole screening length, the static potential and the profile of the color electric flux tube. We furthermore derive the low-energy effective monopole action. Marked differences between the quenched and dynamical vacuum are found.

We report first measurements of $e^{+}{e}^{-}\to D^{(*)+}{D}^{(*)-}$ processes far above threshold. The cross sections for $e^{+}{e}^{-}\to D_T^{*+}{D}_L^{*-}$ and $e^{+}{e}^{-}\to D^{+}{D}_T^{*-}$ at $\sqrt{s}\simeq 10.6\mathrm{G}\mathrm{e}\mathrm{V}/c^2$ are measured to be $0.55\pm 0.03\pm 0.05$ and $0.62\pm 0.03\pm 0.06\mathrm{p}\mathrm{b}$, respectively. We set upper limits on the cross sections for $e^{+}{e}^{-}\to D_T^{*+}{D}_T^{*-}$, $e^{+}{e}^{-}\to D_L^{*+}{D}_L^{*-}$, $e^{+}{e}^{-}\to D^{+}{D}_L^{*-}$, and $e^{+}{e}^{-}\to D^{+}{D}^{-}$ processes. The analysis is based on $88.9{\mathrm{f}\mathrm{b}}^{-1}$ of data collected by the Belle experiment at the KEKB $e^{+}{e}^{-}$ asymmetric collider.

Braneworld models in extra dimensions can be tested in laboratory by the coupling of the radion to the standard model fields. The identification of the radion as a canonically normalized field involves a careful general relativity treatment: if a bulk scalar is responsible for the stabilization of the system, its fluctuations are entangled with the perturbations of the metric and they also have to be taken into account (similarly to the well-developed theory of scalar metric perturbations in 4D cosmology with a scalar field). Extracting a proper dynamical variable in a warped geometry/scalar setting is a nontrivial task, performed so far only in the limit of negligible backreaction of the scalar field on the background geometry. We perform the general calculation, diagonalizing the action up to second order in the perturbations and identifying the physical eigenmodes of the system for any amplitude of the bulk scalar. This computation allows us to derive a very simple expression for the exact coupling of the eigenmodes to the standard model fields on the brane, valid for an arbitrary background configuration. As an application, we discuss the Goldberger-Wise mechanism for the stabilization of the radion in the Randall-Sundrum–type models. The existing studies, limited to small amplitude of the bulk scalar field, are characterized by a radion mass which is significantly below the physical scale at the observable brane. We extend them beyond the small backreaction regime. For intermediate amplitudes, the radion mass approaches the electroweak scale, while its coupling to the observable brane remains nearly constant. At very high amplitudes, the radion mass instead decreases, while the coupling sharply increases. Severe experimental constraints are expected in this regime.

An exact four-dimensional black hole solution of gravity with a minimally coupled self-interacting scalar field is reported. The event horizon is a surface of negative constant curvature enclosing the curvature singularity at the origin, and the scalar field is regular everywhere outside the origin. This solution is an asymptotically locally anti-deSitter spacetime. The strong energy condition is satisfied on and outside the event horizon. The thermodynamical analysis shows the existence of a critical temperature, below which a black hole in vacuum undergoes a spontaneous dressing up with a nontrivial scalar field in a process reminiscent of ferromagnetism.

We show that some novel physics of supertubes removes closed timelike curves from many supersymmetric spaces which naively suffer from this problem. The main claim is that supertubes naturally form domain walls, so while analytical continuation of the metric would lead to closed timelike curves, across the domain wall the metric is nondifferentiable, and the closed timelike curves are eliminated. In the examples we study, the metric inside the domain wall is always of the Gödel type, while outside the shell it looks like a localized rotating object, often a rotating black hole. Thus this mechanism prevents the appearance of closed timelike curves behind the horizons of certain rotating black holes.

We present an alternative way of tracing the existence of a scalar field based on the analysis of the gravitational wave spectrum of a vibrating neutron star. Scalar-tensor theories in strong-field gravity can potentially introduce much greater differences in the parameters of a neutron star than the uncertainties introduced by the various equations of state. The detection of gravitational waves from neutron stars can set constraints on the existence and the strength of scalar fields. We show that the oscillation spectrum is dramatically affected by the presence of a scalar field, and can provide unique confirmation of its existence.

We investigate the localization of 4D topological global defects on the brane embedded in 5D. The defects are induced by 5D scalar fields with a symmetry-breaking potential. Taking an Ansatz which separates the scalar field into the 4D and the extra-D part, we find that the static-hedgehog configuration is accomplished and the defects are formed only in the ${\mathrm{A}\mathrm{d}\mathrm{S}}_4/{\mathrm{A}\mathrm{d}\mathrm{S}}_5$ background. In the extra dimension, the localization amplitude for the 4D defects is high where the warp factor is high.