There are two main sets of data for the observed spectrum of ultrahigh energy cosmic rays (those cosmic rays with energies greater than $\sim 4\times {10}^{18}$ eV), the high resolution Fly’s Eye (HiRes) Collaboration group observations, which seem to be consistent with the predicted theoretical spectrum (and therefore with the theoretical limit known as the Greisen-Zatsepin-Kuzmin cutoff), and the observations from the Akeno Giant Air Shower Array (AGASA) Collaboration group, which reveal an abundant flux of incoming particles with energies above $1\times {10}^{20}$ eV, violating the Greisen-Zatsepin-Kuzmin cutoff. As an explanation of this anomaly it has been suggested that quantum-gravitational effects may be playing a decisive role in the propagation of ultrahigh energy cosmic rays. In this article we take the loop quantum gravity approach. We shall provide some techniques to establish and analyze new constraints on the loop quantum gravity parameters arising from both sets of data, HiRes and AGASA. We shall also study their effects on the predicted spectrum for ultrahigh energy cosmic rays. As a result we will state the possibility of reconciling the AGASA observations.

Cluster number counts offer sensitive probes of the dark energy if and only if the evolution of the cluster mass versus observable relation(s) is well calibrated. We investigate the potential for internal calibration by demanding consistency in the counts as a function of the observable. In the context of a constant dark energy equation of state, the known initial fluctuation amplitude expected from the cosmic microwave background, universal underlying mass function, and an idealized selection, we find that the ambiguity from the normalization of the mass-observable relationships, or an extrapolation of external mass-observable determinations from higher masses, can be largely eliminated with a sufficiently deep survey, even allowing for an arbitrary evolution. More generally, number counts as a function of both the redshift and the observable enable strong consistency tests on assumptions made in modeling the mass-observable relations and cosmology.

For neutrons bound inside nuclei, baryon instability can manifest itself as a decay into undetectable particles (e.g., $\overrightarrow{n}\nu \nu \overline{\nu }),$ i.e., as a disappearance of a neutron from its nuclear state. If electric charge is conserved, a similar disappearance is impossible for a proton. The existing experimental lifetime limit for neutron disappearance is 4–7 orders of magnitude lower than the lifetime limits with detectable nucleon decay products in the final state. In this paper we calculated the spectrum of nuclear de-excitations that would result from the disappearance of a neutron or two neutrons from ${}^{12}\mathrm{C}.$ We found that some de-excitation modes have signatures that are advantageous for detection in the modern high-mass, low-background, and low-threshold underground detectors, where neutron disappearance would result in a characteristic sequence of time- and space-correlated events. Thus, in the KamLAND detector, a time-correlated triple coincidence of a prompt signal, a captured neutron, and a ${\beta }^{+}$ decay of the residual nucleus, all originating from the same point in the detector, will be a unique signal of neutron disappearance allowing searches for baryon instability with sensitivity 3–4 orders of magnitude beyond the present experimental limits.

The right-handed neutrino mass matrix that is central to the understanding of small neutrino masses via the seesaw mechanism can arise either (i) from renormalizable operators or (ii) from nonrenormalizable or super-renormalizable operators, depending on the symmetries and the Higgs content of the theory beyond the standard model. In this paper, we study lepton flavor violating (LFV) effects in the first class of seesaw models wherein the ${\nu }_R$ Majorana masses arise from renormalizable Yukawa couplings involving a $B-L=2\mathrm{}$ Higgs field. We present detailed predictions for $\overrightarrow{\tau }\mu +\gamma$ and $\overrightarrow{\mu }e+\gamma$ branching ratios in these models taking the current neutrino oscillation data into account. Focusing on minimal supergravity models, we find that for a large range of minimal supersymmetric standard model (MSSM) parameters, suggested by the relic abundance of neutralino dark matter which is consistent with Higgs boson mass and other constraints, these radiative decays are in the range accessible to planned experiments. We compare these predictions with lepton flavor violation in the second class of models arising entirely from the Dirac Yukawa couplings. We study the dependence of the ratio $r\equiv B(\overrightarrow{\mu }e+\gamma )/B(\overrightarrow{\tau }\mu +\gamma )$ on the MSSM parameters and show that measurement of r can provide crucial insight into the origin of the seesaw mechanism.

Motivated by recent results on charmed baryons from CLEO and FOCUS, we reexamine the couplings of the orbitally excited charmed baryons. Because of its proximity to the ${\Sigma }_c\pi$ threshold, the strong decays of the ${\Lambda }_c^{+}\mathrm{}\left(2593\right)\mathrm{}$ are sensitive to finite width effects. This distorts the shape of the invariant mass spectrum in ${\Lambda }_{c1\mathrm{}}^{+}\to {\Lambda }_c^{+}{\pi }^{+}{\pi }^{-}$ from a simple Breit-Wigner resonance, which has implications for the experimental extraction of the ${\Lambda }_c^{+}\mathrm{}\left(2593\right)\mathrm{}$ mass and couplings. We perform a fit to unpublished CLEO data which gives $M\left({\Lambda }_c^{+}\mathrm{}\right(2593\left)\mathrm{}\right)-M\left({\Lambda }_c^{+}\right)=305.6\mathrm{}\pm 0.3\mathrm{MeV}$ and $h_2^2{=0.24\mathrm{}}_{-0.11}^{+0.23\mathrm{}},$ with $h_2$ the ${\Lambda }_{c1\mathrm{}}\to {\Sigma }_c\pi$ strong coupling in the chiral Lagrangian. We also comment on the new orbitally excited states recently observed by CLEO.

The pressure of hot QCD has recently been determined to the last perturbatively computable order $g^6\ln g$ by Kajantie et al. using three-dimensional effective theories. A similar method is applied here to the pressure in the presence of small but non-vanishing quark chemical potentials, and the result is used to derive the quark number susceptibilities in the limit $\mu =0.\mathrm{}$ The diagonal quark number susceptibility of QCD with $n_f$ flavors of massless quarks is evaluated to order $g^6\ln g$ and compared with recent lattice simulations. It is observed that the results qualitatively resemble the lattice ones, and that when combined with the fully perturbative but yet undetermined $g^6$ term they may well explain the behavior of the lattice data for a wide range of temperatures.

We study single Higgs boson production in $\gamma \gamma$ collisions proceeding via the hadronic content of the photon. These processes complement previous studies of pair and single Higgs boson production at $e^{+}{e}^{-}$ colliders. For standard model Higgs boson masses of current theoretical interest, the resolved photon contributions are non-negligible in precision cross section measurements. The charged Higgs boson cross sections are not competitive with the $\gamma \overrightarrow{\gamma }{H}^{+}{H}^{-}$ process and at best might offer some information about quark-Higgs couplings. Finally, resolved photon production of the heavier Higgs bosons $H^0$ and $A^0$ of the MSSM can probe regions of the supersymmetry (SUSY) parameter space that will complement other measurements. This last process shows some promise in SUSY Higgs boson searches and warrants further study.

The flux of atmospheric muons and neutrinos is calculated by a three dimensional Monte Carlo simulation with the air shower code CORSIKA using the hadronic interaction models DPMJET, VENUS, GHEISHA, and UrQMD. For the simulation of low energy primary particles the original CORSIKA has been extended by a parametrization of the solar modulation and a microscopic calculation of the directional dependence of the geomagnetic cutoff functions. An accurate description for the geography of the Earth has been included by a digital elevation model, tables for the local magnetic field in the atmosphere, and various atmospheric models for different geographic latitudes and annual seasons. CORSIKA is used to calculate atmospheric muon fluxes for different locations and the neutrino fluxes for Kamioka. The results of CORSIKA for the muon fluxes are verified by an extensive comparison with recent measurements. The neutrino fluxes obtained are compared with results of other calculations, and the influence of the hadronic interaction model, the geomagnetic cutoff, and the local magnetic field on the neutrino fluxes is investigated.

We report experimental details and results of a new measurement of the decay $K^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}{\nu }_e{(K}_{e4\mathrm{}}).\mathrm{}$ A sample of more than $400,000K_{e4\mathrm{}}$ events with low background has been collected by Experiment 865 at the Brookhaven Alternate Gradient Synchrotron. From these data, the branching ratio $(4.11\mathrm{}\pm 0.01\pm 0.11)\times {10}^{-5}$ and the $\pi \pi$ invariant mass dependence of the form factors $F,G,$ and H of the weak hadronic current as well as the phase shift difference ${\delta }_0^0-{\delta }_1^1$ for $\pi \pi$ scattering were extracted. Using constraints based on analyticity and chiral symmetry, a new value with considerably improved accuracy for the s-wave $\pi \pi$ scattering length $a_0^0$ has been obtained also: $a_0^0=0.216\mathrm{}\pm 0.013\left(\mathrm{stat}\right)\pm 0.002\left(\mathrm{syst}\right)\pm 0.002\left(\mathrm{theor}\right).\mathrm{}$

We reexamine the electroweak baryogenesis within the context of the minimal supersymmetric standard model, studying its potential collider signatures. We find that this mechanism of baryogenesis does not give a new $\mathrm{CP}$ violating signal at the B factories. The first circumstantial evidence may come from enhanced $B_s$ or $B_d$ mixing. If a light right-handed scalar top quark and Higgs boson are found as required, a linear collider represents the best possibility for confirming the scenario.

Recently Mendonca and Cardoso [Phys. Rev. D 66, 104009 (2002)] considered nonlinear gravitational wave packets propagating in flat space-time. They concluded that the evolution equation—to third order in amplitude—takes a similar form to what arises in nonlinear optics. Based on this equation, the authors found that nonlinear gravitational waves exhibit self-phase modulation and high harmonic generation leading to frequency up-shifting and spectral energy dilution of the gravitational wave energy. In this Brief Report we point out the fact—a possibility that seems to have been overlooked by Mendonca and Cardoso—that the nonlinear terms in the evolution equation cancels and, hence, that there is no amplitude evolution of the pulse. Finally we discuss scenarios where these nonlinearities may play a role.

We calculate, using holographic duality, the thermal two-point function in finite temperature little string theory. The analysis of those correlators reveals possible instabilities of the thermal ensemble, as in previous discussions of the thermodynamics of little string theory. We comment on the dependence of the instability on the spatial volume of the system.

We study the decay of unstable $\mathrm{D}p$-branes when the world-volume gauge field is turned on. We obtain the relevant $\mathrm{D}p$-brane boundary state with electric and magnetic fields by boosting and rotating the rolling tachyon boundary state of a $\mathrm{D}\left(p-1\right)$-brane and then T dualizing along one of the transverse directions. A simple recipe to turn on the gauge fields in the boundary state is given. We find that the effect of the electric field is to parametrically enhance the coupling of closed string oscillation modes along the electric field direction and provide an intuitive understanding of the result in the T-dualized picture. We also analyze the system by using the effective field theory and compare the result with the boundary state approach.

We study the quantum moduli spaces and dynamical superpotentials of four-dimensional ${\mathrm{SU}\left(2\right)\mathrm{}}^r$ linear and ring moose theories with $\mathcal{N}=1\mathrm{}$ supersymmetry and link chiral superfields in the fundamental representation. Nontrivial quantum moduli spaces and dynamical superpotentials are produced. When the moduli space is perturbed by a generic tree level superpotential, the vacuum space becomes discrete. The ring moose is in the Coulomb phase and we find two singular submanifolds with a nontrivial modulus that is a function of all the independent gauge invariants needed to parametrize the quantum moduli space. The massive theory near these singularities confines. The Seiberg-Witten elliptic curve that describes the quantum moduli space of the ring moose is produced.

In this paper, using the $U\left(1\right)\mathrm{}$ gauge potential decomposition and the $\phi$-mapping topological current theory, the many knotlike vortex lines in Chern-Simons field theory are studied. It has been pointed out that the Chern-Simons action is a topological invariant for the family of knots; i.e., it is just the total sum of all the self-linking and all the linking numbers of the knot family. Furthermore, it is also shown that this Chern-Simons knot topological number is preserved in the branch processes (splitting, merging, and intersection) during the evolution of these knotlike vortex lines.

We argue that the Einstein-Yang-Mills theory presents nontrivial solutions with a NUT charge. These solutions approach asymptotically the Taub-NUT spacetime. They are characterized by the NUT parameter, the mass, and the node numbers of the magnetic potential and present both electric and magnetic potentials. The existence of nontrivial Einstein-Yang-Mills solutions with a NUT charge in the presence of a negative cosmological constant is also discussed. We use the counterterm subtraction method to calculate the boundary energy-momentum tensor and the mass of these configurations. Also, dyon black hole solutions with a nonspherical event horizon topology are shown to exist for a negative cosmological constant.

Considering a real scalar field distribution which is assumed to be locally anisotropic and coupled to a Bianchi type-I background spacetime, the energy density and pressure associated with the anisotropic matter field distribution are evaluated. The vanishing of the expectation values of the nondiagonal components of $T_{\mu \nu }$ allows us to treat the scalar field in complete analogy with the distribution of fluid. The primeval density perturbations produced by the vacuum fluctuations of the scalar field are considered and the Jeans criterion for structure formation is obtained. The metric and matter field perturbations are considered and it is found that for the present anisotropic case the perturbations of the pressure in the radial and tangential directions are different. The Jeans instability is discussed and the Jeans wave number for the present case is evaluated. It is found that for the anisotropic case the Jeans length depends on the velocity of the fluctuations in the radial and transverse directions and thus on the direction of propagation of the perturbations.

We study soft supersymmetry breaking parameters in a supersymmetric unified model which potentially solves the doublet-triplet splitting problem. In the model the doublet-triplet splitting is solved by the discrete symmetry which is allowed to be introduced due to the direct product structure of the gauge group. The messenger fields for the gauge mediated supersymmetry breaking are naturally embedded in the model. The discrete symmetry required by the doublet-triplet splitting makes the gaugino masses nonuniversal and also induces a different mass spectrum for the scalar masses from the ordinary minimal gauge mediation model. Independent physical $\mathrm{CP}$ phases can remain in the gaugino sector even after the R transformation.

A CP-even neutral Higgs boson with standard-model-like couplings may be the lightest scalar of a two-Higgs-doublet model. We study the decoupling limit of the most general CP-conserving two-Higgs-doublet model, where the mass of the lightest Higgs scalar is significantly smaller than the masses of the other Higgs bosons of the model. In this case, the properties of the lightest Higgs boson are nearly indistinguishable from those of the standard model Higgs boson. The first nontrivial corrections to Higgs boson couplings in the approach to the decoupling limit are also evaluated. The importance of detecting such deviations in precision Higgs boson measurements at future colliders is emphasized. We also clarify the case in which a neutral Higgs boson can possess standard-model-like couplings in a regime where the decoupling limit does not apply. The two-Higgs-doublet sector of the minimal supersymmetric model illustrates many of the above features.