Upper limits on doubly charged bilepton couplings and masses are extracted from CERN LEP data for Bhabha scattering in the energy range $\sqrt{s}=183\mathrm{}–202\mathrm{GeV}$ using the standard model program ZFITTER, which calculates radiative corrections. We find that $g_L^2{/M}_L^2<{O(10\mathrm{}}^{-5}){\mathrm{GeV}}^{-2}$ at 95% C.L. for scalar and vector bileptons.

We derive the equations governing the dynamics of cosmic strings in a flat anisotropic universe of Bianchi type I and study the evolution of simple cosmic string loop solutions. We show that the anisotropy of the background can have a characteristic effect in the loop motion. We discuss some cosmological consequences of these findings and, by extrapolating our results to cosmic string networks, we comment on their ability to survive an inflationary epoch, and hence be a possible fossil remnant (still visible today) of an anisotropic phase in the very early Universe.

The color suppressed modes $B^0\to D^{\left(*\right)0\mathrm{}}{\eta }^{(\prime )}$ are analyzed in the perturbative QCD approach. We find that the dominant contribution is from the nonfactorizable diagrams. The branching ratios calculated in our approach for $B^0\to D^{\left(*\right)0\mathrm{}}\eta$ agree with current experiments. By neglecting the gluonic contribution, we predict that the branching ratios of $B^0\to D^{\left(*\right)0\mathrm{}}{\eta }^{\prime }$ are comparable in size to those for $B^0\to D^{\left(*\right)0\mathrm{}}{\pi }^0,$ but smaller than those for $B^0\to D^{\left(*\right)0\mathrm{}}\eta .$

Beyond-constant-mass-approximation solutions for magnetically catalyzed fermion and scalar masses are found in a gauge Higgs-Yukawa theory in the presence of a constant magnetic field. The fermion masses obtained are several orders of magnitude larger than those found in the absence of Yukawa interactions. The masses obtained within the beyond-constant-mass approximation exactly reduce to the results within the constant-mass approach when the condition $\nu \ln (1/m^2)\ll 1$ is satisfied. Possible applications to early universe physics and condensed matter are discussed.

We study an extension of the standard model with one latticized extra dimension accessible to all fields. The model is characterized by the size of the extra dimension and the number of sites, and contains a tower of massive particles. At energies lower than the mass of the new particles there are no tree-level effects. Therefore bounds on the scale of new physics can only be set from one-loop processes. We calculate several observables sensitive to loop effects, such as the $\rho$ parameter, $\overrightarrow{b}s\gamma ,\overrightarrow{Z}b\overline{b},$ and the $B^0\rightleftharpoons B^0$ mixing, and use them to set limits on the lightest new particles for a different number of sites. It turns out that the continuous result is rapidly reached when the extra dimension is discretized in about 10 to 20 sites only. For a small number of sites the bounds placed on the usual continuous scenario can be reduced by roughly a factor of $10\%–25\%,$ which means that the new particles can be as light as $320\mathrm{GeV}.$ Finally, we briefly discuss an alternative model in which fermions do not have additional modes.

We study the top quark decay to a b quark and W boson in the noncommutative standard model. The lowest contribution to the decay comes from the terms quadratic in the matrix describing the noncommutative (NC) effects while the linear term is seen to identically vanish because of symmetry. The NC effects are found to be significant only for low values of the NC characteristic scale.

Within kinetic theory, we look for the local equilibrium configurations of a quark-gluon plasma by maximizing the local entropy. We use the well-established transport equations in the Vlasov limit, supplemented by the Waldmann-Snider collision terms. Two different classes of local equilibrium solutions are found. The first one corresponds to the configurations that comply with the so-called collisional invariants. The second one is given by the distribution functions that cancel the collision terms, representing the most probable binary interactions with soft gluon exchange in the t channel. The two sets of solutions agree with each other if we go beyond these dominant processes and take into account subleading quark-antiquark annihilation or creation and gluon number nonconserving processes. The local equilibrium state appears to be colorful, as the color charges are not locally neutralized. The properties of such an equilibrium state are analyzed. In particular, the related hydrodynamic equations of a colorful fluid are derived. Possible neutralization processes are also briefly discussed.

The biunitary parametrization of the neutrino Dirac mass matrix $m_D$ of the seesaw mechanism of neutrino mass generation is considered in detail. Assuming a hierarchical structure of $m_D$ and of the heavy Majorana neutrino masses $M_{1,2,3}>0,$ $M_1\ll M_2\ll M_3,$ with a strong hierarchy between $M_3$ and $M_1$ ${(M}_3\gg {10}^3{M}_1),$ we find that, in order to produce the observed baryon asymmetry of the Universe via leptogenesis, the scale of $m_D$ should be given by the up-quark masses, $m_D\sim m_{\mathrm{up}}.$ It is also possible to reproduce the low-energy neutrino mixing phenomenology for $m_D\sim m_{\mathrm{up}}$ if one of the heavy Majorana neutrinos is much heavier than the other two and there exists only a rather mild hierarchy between the masses of the latter ${(M}_2\cong 10M_1).\mathrm{}$ In the case of a strong hierarchy between $M_3$ and $M_{1,2},$ successful leptogenesis requires a mild hierarchy between $M_1$ and $M_2$ as well. In this scenario, the effective Majorana mass in neutrinoless double beta decay depends on the CP violating phase controlling the leptogenesis if $m_{D1\mathrm{}}$ is negligible. The lepton flavor violating decays $\overrightarrow{\mu }e+\gamma ,$ $\overrightarrow{\tau }\mu +\gamma$ and $\overrightarrow{\tau }e+\gamma$ are considered and a characteristic relation between their decay rates is predicted. The CP violation effects in neutrino oscillations can be observable. In general, there is no direct connection between the latter and CP violation in leptogenesis. If the CP violating phases of the seesaw model satisfy certain relations, the baryon asymmetry of the Universe and the rephasing invariant $J_{\mathrm{CP}}$ which determines the magnitude of the CP violation effects in neutrino oscillations depend on the same CP violating phase and their signs are correlated.

In two previous papers we have analyzed the C metric in a background with a cosmological constant $\Lambda ,$ namely, the de–Sitter (dS) C metric $(\Lambda >0),$ and the anti–de Sitter (AdS) C metric $(\Lambda <0),$ extending thus the original work of Kinnersley and Walker for the C metric in flat spacetime $(\Lambda =0).\mathrm{}$ These exact solutions describe a pair of accelerated black holes in the flat or cosmological constant background, with the acceleration A being provided by a strut in between that pushes away the two black holes or, alternatively, by strings hanging from infinity that pull them in. In this paper we analyze the extremal limits of the C metric in a background with a generic cosmological constant $\Lambda >0,\Lambda =0,$ and $\Lambda <0.\mathrm{}$ We follow a procedure first introduced by Ginsparg and Perry in which the Nariai solution, a spacetime which is the direct topological product of the two-dimensional dS and a two-sphere, is generated from the four-dimensional dS-Schwarzschild solution by taking an appropriate limit, where the black hole event horizon approaches the cosmological horizon. Similarly, one can generate the Bertotti-Robinson metric from the Reissner-Nordström metric by taking the limit of the Cauchy horizon going into the event horizon of the black hole, as well as the anti-Nariai metric by taking an appropriate solution and limit. Using these methods we generate the C-metric counterparts of the Nariai, Bertotti-Robinson, and anti-Nariai solutions, among others. These C-metric counterparts are conformal to the product of two two-dimensional manifolds of constant curvature, the conformal factor depending on the angular coordinate. In addition, the C-metric extremal solutions have a conical singularity at least at one of the poles of their angular surfaces. We give a physical interpretation to these solutions, e.g., in the Nariai C metric (with topology ${\mathrm{dS}}_2\times {\tilde{S}}^2)$ to each point in the deformed two-sphere ${\widetilde{\stackrel{̃}{S}}}^2$ corresponds a ${\mathrm{dS}}_2$ spacetime, except for one point which corresponds to a ${\mathrm{dS}}_2$ spacetime with an infinite straight strut or string. There are other important new features that appear. One expects that the solutions found in this paper are unstable and decay into a slightly nonextreme black hole pair accelerated by a strut or by strings. Moreover, the Euclidean version of these solutions mediate the quantum process of black hole pair creation that accompanies the decay of the dS and AdS spaces.

This work addresses the problem of generically tracking black hole event horizons in computational simulation of black hole interactions. Solutions of the hyperbolic eikonal equation, solved on a curved spacetime manifold containing black hole sources, are employed in development of a robust tracking method capable of continuously monitoring arbitrary changes of topology in the event horizon as well as arbitrary numbers of gravitational sources. The method makes use of continuous families of level set viscosity solutions of the eikonal equation with identification of the black hole event horizon obtained by the signature feature of discontinuity formation in the eikonal’s solution. The method is employed in the analysis of the event horizon for the asymmetric merger in a binary black hole system. In this first such three dimensional analysis, we establish both qualitative and quantitative evidence for our method and its application to the asymmetric problem. We focus attention on (1) the topology of the throat connecting the holes following merger, (2) the time of merger, and (3) continuing to account for the surface of section areas of the black hole sources.

I explore properties of the inflationary flow equations. I show that the flow equations do not correspond directly to inflationary dynamics. Nevertheless, they can be used as a rather complicated algorithm for generating inflationary models. I demonstrate that the flow equations can be solved analytically and give a closed form solution for the potentials to which flow equation solutions correspond. I end by considering some simpler algorithms for generating stochastic sets of slow-roll inflationary models for confrontation with observational data.

We reconsider the issue of the number of e-foldings before the end of inflation at which observable perturbations were generated. We determine a plausible upper limit on that number for the standard cosmology which is around 60, with the expectation that the actual value will be up to 10 below this. We also note a special property of the $\lambda {\phi }^4$ model which reduces the uncertainties in that case and favors a higher value, giving a fairly definite prediction of 64 e-foldings for that model. We note an extreme (and highly implausible) situation where the number of e-foldings can be even higher, possibly up to 100, and discuss the shortcomings of quantifying inflation by e-foldings rather than by the change in $\mathrm{aH}.\mathrm{}$ Finally, we discuss the impact of nonstandard evolution between the end of inflation and the present, showing that again the expected number of e-foldings can be modified, and in some cases significantly increased.

We present a general framework for analyzing spatially inhomogeneous cosmological dynamics. It employs Hubble-normalized scale-invariant variables which are defined within the orthonormal frame formalism, and leads to the formulation of Einstein’s field equations with a perfect fluid matter source as an autonomous system of evolution equations and constraints. This framework incorporates spatially homogeneous dynamics in a natural way as a special case, thereby placing earlier work on spatially homogeneous cosmology in a broader context, and allows us to draw on experience gained in that field using dynamical systems methods. One of our goals is to provide a precise formulation of the approach to the spacelike initial singularity in cosmological models, described heuristically by Belinskiǐ, Khalatnikov and Lifshitz. Specifically, we construct an invariant set which we conjecture forms the local past attractor for the evolution equations. We anticipate that this new formulation will provide the basis for proving rigorous theorems concerning the asymptotic behavior of spatially inhomogeneous cosmological models.

Network data analysis methods are the only way to properly separate real gravitational wave (GW) transient events from detector noise. They can be divided into two generic classes: the coincidence method and the coherent analysis. The former uses lists of selected events provided by each interferometer belonging to the network and tries to correlate them in time to identify a physical signal. Instead of this binary treatment of detector outputs (signal present or absent), the latter method involves first the merging of the interferometer data and looks for a common pattern, consistent with an assumed GW waveform and a given source location in the sky. The thresholds are only applied later, to validate or not the hypothesis made. As coherent algorithms use more complete information than coincidence methods, they are expected to provide better detection performances, but at a higher computational cost. An efficient filter must yield a good compromise between a low false alarm rate (hence triggering on data at a manageable rate) and a high detection efficiency. Therefore, the comparison of the two approaches is achieved using so-called receiving operating characteristics (ROC), giving the relationship between the false alarm rate and the detection efficiency for a given method. This paper investigates this question via Monte Carlo simulations, using the network model developed in a previous article. Its main conclusions are the following. First, a three-interferometer network such as Virgo-LIGO is found to be too small to reach good detection efficiencies at low false alarm rates: larger configurations are suitable to reach a confidence level high enough to validate as true GW a detected event. In addition, an efficient network must contain interferometers with comparable sensitivities: studying the three-interferometer LIGO network shows that the 2-km interferometer with half sensitivity leads to a strong reduction of performances as compared to a network of three interferometers with full sensitivity. Finally, it is shown that coherent analyses are feasible for burst searches and are clearly more efficient than coincidence strategies. Therefore, developing such methods should be an important goal of a worldwide collaborative data analysis.

The DELPHI Collaboration has recently reported the measurement of $J/\psi$ production in photon-photon collisions at CERN LEP II. These newly available data provide additional proof of the importance of colored $c\overline{c}$ pairs for the production of charmonium, because these data can be explained only by considering resolved photon processes. We show here that the inclusion of color octet contributions to $J/\psi$ production in the framework of the color evaporation model is able to reproduce these data. In particular, the transverse-momentum distribution of the $J/\psi$ mesons is well described by this model.

The dependence of the T-odd correlation on the effective Lagrangian parameters in the $K^{+}\to \pi l\nu \gamma ,l=e,\mu ,$ decays is analyzed. It is shown that the observable introduced is a perspective in the search for new physics in the vector and pseudovector sectors of the Lagrangian. As for the scalar and pseudoscalar sectors, T-odd correlation studies will not allow one to improve current restrictions on the parameters of models beyond the standard model.

The first AMS flight in June 1998 on board the space shuttle Discovery at an altitude of approximately 380 km unveiled unexpected features of the cosmic rays spectra below Earth’s geomagnetic cutoff. In addition to a secondary flux of particles at all latitudes, a ring of high energy particles (up to 6 GeV) and an anomalous ratio $e^{+}{/e}^{-}$ as high as 4 was observed near the geomagnetic equator. This paper describes a simulation of the interaction of primary cosmic rays with the atmosphere in which the effect of Earth’s magnetic field is included. Using the GEANT3 package for the tracking of particles with the GFLUKA associated package for the physics of interactions, this simulation reproduces quite well the AMS experimental results and the CAPRICE muon data at ground level. The predictions of this model for the flux of atmospheric neutrinos are compared with the Super-Kamiokande results and with the results of other atmospheric neutrino models.

We discuss the prospects for next generation neutrino telescopes, such as IceCube, to measure the flavor ratios of high-energy astrophysical neutrinos. The expected flavor ratios at the sources are ${\phi }_{{\nu }_e}:{\phi }_{{\nu }_{\mu }}:{\phi }_{{\nu }_{\tau }}=1:2:0,$ and neutrino oscillations quickly transform these to $1:1:1.$ The flavor ratios can be deduced from the relative rates of showers $({\nu }_e$ charged current, most ${\nu }_{\tau }$ charged current, and all flavors neutral current), muon tracks $({\nu }_{\mu }$ charged current only), and tau lepton lollipops and double bangs $({\nu }_{\tau }$ charged current only). The peak sensitivities for these interactions are at different neutrino energies, but the flavor ratios can be reliably connected by a reasonable measurement of the spectrum shape. Measurement of the astrophysical neutrino flavor ratios tests the assumed production mechanism and also provides a very long baseline test of a number of exotic scenarios, including neutrino decay, CPT violation, and small-$\delta m^2$ oscillations to sterile neutrinos.

We investigate in detail the $\gamma \gamma$ fusion production mechanisms of two neutral Higgs bosons ${(h}^0{A}^0,$ $H^0{A}^0,$ $h^0{H}^0,$ and $H^0{H}^0)$ within the framework of the minimal supergravity–inspired minimal supersymmetric standard model at an $e^{+}{e}^{-}$ linear colliders (LC), which provide a probe of the trilinear Higgs self-couplings. We calculate the dependence of the production rates on the Higgs boson masses, the ratio of the vacuum expectation values $\tan \beta ,$ and the c.m.s. energy $\sqrt{s}.$ We find that the cross section for the $H^0{H}^0$ production at a LC can reach 0.2 fb, while the cross section of $A^0{H}^0$ production is only ${10}^{-4}–{10}^{-3}\mathrm{fb}$ with our parameters.

We analyze the impact of the data on long-baseline ${\nu }_{\mu }$ disappearance from the K2K experiment and reactor ${\overline{\nu }}_e$ disappearance from the KamLAND experiment on the determination of the leptonic three-generation mixing parameters. Performing an up-to-date global analysis of solar, atmospheric, reactor, and long-baseline neutrino data in the context of three-neutrino oscillations, we determine the presently allowed ranges of masses and mixing and we consistently derive the allowed magnitude of the elements of the leptonic mixing matrix. We also quantify the maximum allowed contribution of $\Delta m_{21}^2$ oscillations to CP-odd and CP-even observables at future long-baseline experiments.