As it follows from the classical analysis, the typical final state of a dark energy universe where a dominant energy condition is violated is a finite-time, sudden future singularity (a big rip). For a number of dark energy universes (including scalar phantom and effective phantom theories as well as specific quintessence models) we demonstrate that quantum effects play the dominant role near a big rip, driving the universe out of a future singularity (or, at least, moderating it). As a consequence, the entropy bounds with quantum corrections become well defined near a big rip. Similarly, black hole mass loss due to phantom accretion is not so dramatic as was expected: masses do not vanish to zero due to the transient character of the phantom evolution stage. Some examples of cosmological evolution for a negative, time-dependent equation of state are also considered with the same conclusions. The application of negative entropy (or negative temperature) occurrence in the phantom thermodynamics is briefly discussed.

We study a supergravity model of inflation essentially depending on one parameter which can be identified with the slope of the potential at the origin. In this type of models the inflaton rolls at high energy from negative values and a positive curvature potential. At some point defined by the equation $\eta =1$ inflation starts. The potential curvature eventually changes to negative values and inflation ends when $\eta =-1$. No spontaneous symmetry breaking type mechanism for inflation of the new type to occur is here required. The model naturally gives a bounded total number of e-folds which is typically close to the required number for observable inflation and it is independent of the initial conditions for the inflaton. The energy scale introduced is fixed by the amplitude of the anisotropies and is of the order of the supersymmetry breaking scale. The model can also accommodate a spectral index bigger or smaller than 1 without extreme fine tuning. We show that it is possible to obtain reasonable numbers for cosmological parameters and, as an example, we reproduce values obtained recently by Tegmark et al., from WMAP and SDSS data alone.

Recently, the notion that the number of vacua is astronomical has received increased attentions, which may be regarded as a possible anthropical explanation to incredibly small cosmological constant. Further, a dynamical mechanism to implement this possibility is required. We show in an operable model of cyclic universe that the universe can experience many cycles with different vacua, which is a generic behavior independent of the details of the model. This might provide a distinct dynamical approach to an anthropically favorable vacuum.

We study the properties of light mesons in the scalar, pseudoscalar, and vector channels within the light-front quantization, by using the (one flavor) Nambu-Jona-Lasinio model with vector interaction. After taking into account the effects of chiral symmetry breaking, we derive the bound-state equation in each channel in the large $N$ limit ($N$ is the number of colors), which means that we consider the lowest $q\overline{q}$ Fock state with the constituent quark and antiquark. By solving the bound-state equation, we simultaneously obtain a mass and a light cone (LC) wave function of the meson. While we reproduce the previous results for the scalar and pseudoscalar mesons, we find that, for a vector meson, the bound-state equations for the transverse and longitudinal polarizations look different from each other. However, eventually after imposing a cutoff which is invariant under the parity and boost transformations, one finds these two are identical, giving the same mass and the same (spin-independent) LC wave function. When the vector interaction becomes larger than a critical value, the vector state forms a bound state, whose mass decreases as the interaction becomes stronger. While the LC wave function of the pseudoscalar meson is broadly distributed in longitudinal momentum ($x$) space, that of the vector meson is squeezed around $x=1/2$.

In the leading order of the $(1/m_b)$-expansion in HQET the dominant contribution to the semi-inclusive decays of polarized ${\Lambda }_b$ baryons into the charm-strangeness mesons $D_s$ and $D_s^{*}$ is given by the partonic process $b(\uparrow )\to c+(D_s^{-},D_s^{*-})$. Using standard values for the parameters of the process one expects a rather large branching ratio of $\approx 8\%$ into these two channels. In the factorization approximation the semi-inclusive decay of a polarized ${\Lambda }_b$ is governed by three unpolarized and four polarized structure functions for which we determine the nonperturbative $O(1/m_b^2)$ corrections and the $O({\alpha }_s)$ radiative corrections. We find that the perturbative and nonperturbative corrections amount to $\approx 10\%$ and $\approx 3\%$, respectively. The seven structure functions can be measured through an analysis of the joint decay distributions of the process involving the polarization of the ${\Lambda }_b$ and the decays $D_s^{*-}\to D_s^{-}+\gamma$ and $D_s^{*-}\to D_s^{-}+{\pi }^0$ for which we provide explicit forms. We also provide numerical results for the Cabibbo-suppressed semi-inclusive decays ${\Lambda }_b\to X_u+(D_s,D_s^{*})$.

We consider electromagnetic corrections to the nonleptonic kaon decay, $K^{+}\to {\pi }^{+}{\pi }^0{\pi }^0$, due to explicit virtual photons only. The decay amplitude is calculated at a one-loop level in the framework of chiral perturbation theory. The interest in this process is twofold: It is actually measured by the NA48 Collaboration from one side, and, the value of the amplitude at the $\pi \pi$ threshold gives access to $\pi \pi$ scattering lengths from the other side. We found that the present correction is about 5 to 6% the value of the Born amplitude squared. Combined with another paper published recently, this fixes the size of the isospin breaking correction to the amplitude squared to 7% its one-loop level value in the absence of isospin breaking and at the center of the Dalitz plot.

We discuss a possibility of large electroweak penguin contribution in $B\to K\pi$ and $\pi \pi$ from recent experimental data. The experimental data may be suggesting that there are some discrepancies between the data and theoretical estimation in the branching ratios of them. In $B\to K\pi$ decays, to explain it, a large electroweak penguin contribution and large strong phase differences seem to be needed. The contributions should appear also in $B\to \pi \pi$. We show, as an example, a solution to solve the discrepancies in both $B\to K\pi$ and $B\to \pi \pi$. However the magnitude of the parameters and the strong phase estimated from experimental data are quite large compared with the theoretical estimations. It may be suggesting some new physics effects are included in these processes. We will have to discuss about the dependence of the new physics. To explain both modes at once, we may need large electroweak penguin contribution with new weak phases and some SU(3) breaking effects by new physics in both QCD and electroweak penguin-type processes.

We present new measurements of $K_L$ semileptonic form factors using data collected in 1997 by the KTeV (E832) experiment at Fermilab. The measurements are based on $1.9\times {10}^6$ $K_L\to {\pi }^{\pm }{e}^{\mp }\nu$ and $1.5\times {10}^6$ $K_L\to {\pi }^{\pm }{\mu }^{\mp }\nu$ decays. For $f_{+}(t)$, we measure both a linear and quadratic term: ${\lambda }_{+}^{\prime }=(20.64\pm 1.75)\times {10}^{-3}$ and ${\lambda }_{+}^{\prime \prime }=(3.20\pm 0.69)\times {10}^{-3}$. For $f_0(t)$, we find ${\lambda }_0=(13.72\pm 1.31)\times {10}^{-3}$. These form factors are consistent with $K^{\pm }$ form factors, suggesting that isospin symmetry breaking effects are small. We use our measured values of the form factors to evaluate the decay phase space integrals, $I_K^e=0.15350\pm 0.00105$ and $I_K^{\mu }=0.10165\pm 0.00080$, where errors include uncertainties arising from the form factor parametrizations.

We present new measurements of the six largest branching fractions of the $K_L$ using data collected in 1997 by the KTeV experiment (E832) at Fermilab. The results are $B(K_L\to {\pi }^{\pm }{\mathrm{e}}^{\mp }\nu )=0.4067\pm 0.0011$, $B(K_L\to {\pi }^{\pm }{\mu }^{\mp }\nu )=0.2701\pm 0.0009$, $B(K_L\to {\pi }^{+}{\pi }^{-}{\pi }^0)=0.1252\pm 0.0007$, $B(K_L\to {\pi }^0{\pi }^0{\pi }^0)=0.1945\pm 0.0018$, $B(K_L\to {\pi }^{+}{\pi }^{-})=(1.975\pm 0.012)\times {10}^{-3}$, and $B(K_L\to {\pi }^0{\pi }^0)=(0.865\pm 0.010)\times {10}^{-3}$, where statistical and systematic errors have been summed in quadrature. We also determine the $CP$ violation parameter $|{\eta }_{+-}|$ to be $(2.228\pm 0.010)\times {10}^{-3}$. Several of these results are not in good agreement with averages of previous measurements.

First principle study of QCD at finite temperature $T$ and chemical potential $\mu$ is essential for understanding a wide range of phenomena from heavy-ion collisions to cosmology and neutron stars. However, in the presence of finite density, the critical behavior lattice gauge theory without species doubling, is unknown. At strong coupling, we examine the phase structure on the $(\mu ,T)$ plane, using Hamiltonian lattice QCD with Wilson fermions. A tricritical point is found, separating the first and second order chiral phase transitions. Such a tricritical point at finite $T$ has not been found in previous work in the Hamiltonian formalism with Kogut-Susskind fermions or naive fermions.

The problem of computing the effective nonrelativistic potential $U_D$ for the interaction of charged-scalar bosons, within the context of $D$-dimensional electromagnetism with a cutoff, is reduced to quadratures. It is shown that $U_3$ cannot bind a pair of identical charged-scalar bosons; nevertheless, numerical calculations indicate that boson-boson bound states do exist in the framework of three-dimensional higher-derivative electromagnetism augmented by a topological Chern-Simons term.

We consider a picture in which the transition from a big crunch to a big bang corresponds to the collision of two empty orbifold planes approaching each other at a constant nonrelativistic speed in a locally flat background space-time, a situation relevant to recently proposed cosmological models. We show that $p$-brane states which wind around the extra dimension propagate smoothly and unambiguously across the orbifold plane collision. In particular we calculate the quantum mechanical production of winding M2-branes extending from one orbifold to the other. We find that the resulting density is finite and that the resulting gravitational backreaction is small. These winding states, which include the string theory graviton, can be propagated smoothly across the transition using a perturbative expansion in the membrane tension, an expansion which from the point of view of string theory is an expansion in inverse powers of ${\alpha }^{\prime }$. The conventional description of a crunch based on Einstein general relativity, involving Kasner or mixmaster behavior is misleading, we argue, because general relativity is only the leading order approximation to string theory in an expansion in positive powers of ${\alpha }^{\prime }$. In contrast, in the M theory setup we argue that interactions should be well behaved because of the smooth evolution of the fields combined with the fact that the string coupling tends to zero at the crunch. The production of massive Kaluza-Klein states should also be exponentially suppressed for small collision speeds. We contrast this good behavior with that found in previous studies of strings in Lorentzian orbifolds.

We present three-dimensional simulations of Einstein's equations implementing a symmetric hyperbolic system of equations with dynamical lapse. The numerical implementation makes use of techniques that guarantee linear numerical stability for the associated initial-boundary value problem. The code is first tested with a gauge wave solution, where rather larger amplitudes and for significantly longer times are obtained with respect to other state of the art implementations. Additionally, by minimizing a suitably defined energy for the constraints in terms of free constraint-functions in the formulation one can dynamically single out preferred values of these functions for the problem at hand. We apply the technique to fully three-dimensional simulations of a stationary black hole spacetime with excision of the singularity, considerably extending the lifetime of the simulations.

We study the reionization scenario in which ionizing UV photons emitted from decaying particle, in addition to usual contributions from stars and quasars, ionize the universe. It is found that the scenario is consistent with both the first year data of the Wilkinson Microwave Anisotropy Probe and the fact that the universe is not fully ionized until $z\sim 6$ as observed by Sloan Digital Sky Survey. Likelihood analysis revealed that rather broad parameter space can be chosen. This scenario will be discriminated by future observations, especially by the EE polarization power spectrum of cosmic microwave background radiation.

Observations of anisotropies in the cosmic microwave background by the Wilkinson Microwave Anisotropy Probe suggest the possibility of oscillations in the primordial curvature perturbation. Such deviations from the usually assumed scale-free spectrum were predicted in the multiple inflation model wherein “flat direction” fields undergo rapid phase transitions due to the breaking of supersymmetry by the large vacuum energy driving inflation. This causes sudden changes in the mass of the (gravitationally coupled) inflaton and interrupts its slow roll. We calculate analytically the resulting modifications to the curvature perturbation and demonstrate how the oscillations arise.

We revise the statistical properties of the primordial cosmological density anisotropies that, at the time of matter-radiation equality, seeded the gravitational development of large scale structures in the otherwise homogeneous and isotropic Friedmann-Robertson-Walker flat universe. Our analysis shows that random fluctuations of the density field at the same instant of equality and with comoving wavelength shorter than the causal horizon at that time can naturally account, when globally constrained to conserve the total mass (energy) of the system, for the observed scale invariance of the anisotropies over cosmologically large comoving volumes. Statistical systems with similar features are generically known as glasslike or latticelike. Obviously, these conclusions conflict with the widely accepted understanding of the primordial structures reported in the literature, which requires an epoch of inflationary cosmology to precede the standard expansion of the universe. The origin of the conflict must be found in the widespread, but unjustified, claim that scale invariant mass (energy) anisotropies at the instant of equality over comoving volumes of cosmological size, larger than the causal horizon at the time, must be generated by fluctuations in the density field with comparably large comoving wavelength.

We note that detector depth can influence the decay path length available for the primary and secondary particles that are the source of atmospheric neutrinos. As a consequence there is a location dependent modulation to the neutrino flux.

We study the determination of $\gamma$ from CP-violating observables in $B\to {\pi }^{+}{\pi }^{-}$ and $B\to \psi K_S$. This determination requires theoretical input to one combination of hadronic parameters. We show that a mild assumption about this quantity may allow bounds to be placed on $\gamma$, but we stress the pernicious effects that an eightfold discrete ambiguity has on such an analysis. The bounds are discussed as a function of the direct ($C$) and interference ($S$) CP-violating observables obtained from time-dependent $B\to {\pi }^{+}{\pi }^{-}$ decays, and their behavior in the presence of new physics effects in $B-\overline{B}$ mixing is studied.

Assuming string theorists will not soon provide a compelling case for the primary theory underlying particle physics, the field will proceed as it has historically: with data stimulating and testing ideas. Ideally the soft supersymmetry breaking Lagrangian will be measured and its patterns will point to the underlying theory. But there are two new problems. First a matter of principle: the theory may be simplest at distance scales and in numbers of dimensions where direct experiments are not possible. Second a practical problem: in the foreseeable future (with mainly hadron collider data) too few observables can be measured to lead to direct connections between experiment and theory. In this paper we discuss and study these issues and consider ways to circumvent the problems, studying models to test methods. We propose a semiquantitative method for focusing and sharpening thinking when trying to relate incomplete data to incomplete theory, as will probably be necessary.

A resonance $X(3872)$, first observed in the decays $B\to KX$, has been seen to decay to $J/\psi {\pi }^{+}{\pi }^{-}$. The ${\pi }^{+}{\pi }^{-}$ mass spectrum peaks near its kinematic upper limit, prompting speculation that the dipion system may be in a ${\rho }^0$. The decay $X(3872)\to J/\psi \omega$ also has been observed. The reaction $\gamma \gamma \to J/\psi {\pi }^{+}{\pi }^{-}$ has been studied. Consequently, angular distributions in decays of $J/\psi ({\rho }^0,\omega )$ states near threshold are of interest, and results are presented.