We study flop transitions for M-theory on Calabi-Yau threefolds and their applications to cosmology in the context of the effective five-dimensional supergravity theory. In particular, the additional hypermultiplet which becomes massless at the transition is included in the effective action. We find the potential for this hypermultiplet which includes quadratic and quartic terms as well as additional dependence on the Kähler moduli. By constructing explicit cosmological solutions, it is demonstrated that a flop transition can indeed be achieved dynamically, as long as the hypermultiplet is set to zero. For an explicit example we find that once excitations of the hypermultiplet are taken into account, the transition is generically not completed but the system is classically stabilized close to the transition region, at least as long as the transition states do not vanish. Regions of moduli space close to flop transitions can, therefore, be viewed as preferred by the cosmological evolution.

It would be extremely useful to know whether a particular low energy effective theory might have come from a compactification of a higher dimensional space. Here, this problem is approached from the ground up by considering theories with multiple interacting massive gravitons. It is actually very difficult to construct discrete gravitational dimensions which have a local continuum limit. In fact, any model with only nearest neighbor interactions is doomed. If we could find a non-linear extension for the Fierz-Pauli Lagrangian for a graviton of mass $m_g,$ which does not break down until the scale ${\Lambda }_2=\sqrt{m_g{M}_{\mathrm{Pl}}},$ this could be used to construct a large class of models whose continuum limit is local in the extra dimension. But this is shown to be impossible: a theory with a single graviton must break down by ${\Lambda }_3{=(m}_g^2{M}_{\mathrm{Pl}}{)}^{1/3}.$ Next, we look at how the discretization prescribed by the truncation of the Kaluza-Klein tower of an honest extra dimension raises the scale of strong coupling. It dictates an intricate set of interactions among various fields which conspire to soften the strongest scattering amplitudes and allow for a local continuum limit, at least at the tree level. A number of candidate symmetries associated with locality in the discretized dimension are also discussed.

We study the general features of a dynamics of a phantom field in the cosmological context. In the case of an inverse coshyperbolic potential, we demonstrate that the phantom field can successfully drive the observed current accelerated expansion of the Universe with the equation of state parameter $w_{\phi }<-1.$ The de Sitter universe turns out to be the late time attractor of the model. The main features of the dynamics are independent of the initial conditions and the parameters of the model. The model fits the supernova data very well, allowing for $-2.4<\mathrm{}{w}_{\phi }<-1$ at a 95% confidence level.

We examine the particle production during tunneling in quantum cosmology. We consider a minisuperspace model with a massive, conformally coupled scalar field and a uniform radiation background. In this model, we construct a semiclassical wave function describing a small recollapsing universe and a nucleated inflating universe (“tunneling from something”). We find that the quantum states of the scalar field in both the initial and the nucleated universe are close to the adiabatic vacuum, the number of created particles is small, and their backreaction on the metric is negligible. We show that the use of the semiclassical approximation is justified for this wave function. Our results imply that the creation of the universe from nothing can be understood as a limit of tunneling from a small recollapsing universe.

An expanding closed universe filled with radiation can either recollapse or tunnel to the regime of unbounded expansion, if the cosmological constant is nonzero. We reexamine the question of particle creation during tunneling, with the purpose of resolving a long-standing controversy. Using a perturbative superspace model with a conformally coupled massless scalar field, which is known to give no particle production, we explicitly show that the breakdown of the semiclassical approximation and the “catastrophic particle production” claimed earlier in the literature are due to an inappropriate choice of the initial quantum state prior to the tunneling.

A Fermi ball is a kind of nontopological soliton which is thought to arise from the spontaneous breaking of an approximate $Z_2$ symmetry and to contribute to cold dark matter. We consider a simple model in which fermion fields with multiflavors are coupled to a scalar field through Yukawa coupling and examine how the number of the fermion flavors affects the stability of the Fermi ball against the fragmentation. (1) We find that the Fermi ball is stable against fragmentation in most cases even in the lowest-order thin-wall approximation. (2) We then find that in the other specific cases the stability is marginal in the lowest-order thin-wall approximation, and the next-to-leading order correction determines the stable region of the coupling constants; we examine the simplest case where the total fermion number $N_i$ and the Yukawa coupling constant $G_i$ of each flavor i are common to the flavors, and find that the Fermi ball is stable in a limited region of the parameters and has the broader region for the larger number of flavors.

Experience with core-collapse supernova simulations shows that accurate accounting of total particle number and 4-momentum can be a challenge for computational radiative transfer. This accurate accounting would be facilitated by the use of particle number and 4-momentum transport equations that allow transparent conversion between volume and surface integrals in both configuration and momentum space. Such conservative formulations of general relativistic kinetic theory in multiple spatial dimensions are presented in this paper, and their relevance to core-collapse supernova simulations is described.

In the standard model, we study CP violating rate asymmetries in the decay $\overrightarrow{b}{\mathrm{dl}}^{+}{l}^{-}$ when one of the leptons is polarized. We find an asymmetry of (5–15)% in the polarized decay spectrum which is comparable to the known results for the unpolarized case. In the kinematic region separating the $\rho -\omega$ and $c\overline{c}$ resonances, which is also theoretically cleanest, the polarized contribution to the asymmetry is larger than the unpolarized results. In order to observe a $3\sigma$ signal for direct CP violation in the polarized spectrum, assuming 100% efficiency, about ${10}^{10}$ $B\overline{B}$ pairs are required at a B factory. Our results indicate an asymmetric contribution from the individual polarization states to the unpolarized CP asymmetry. Taking advantage of this, one can attribute any new physics to be most sensitive to a specific polarization state.

Within the standard model (SM), the time-dependent $\mathrm{CP}$ asymmetries in $\overrightarrow{B}\psi K_S,$ $\overrightarrow{B}{\eta }^{\prime }{K}_S,$ and $\overrightarrow{B}\phi K_S$ are expected to give the same result, i.e., $\sin 2\beta .$ However, recent measurements of the mixing-induced $\mathrm{CP}$ asymmetries in $\overrightarrow{B}\phi K_S$ and $\overrightarrow{B}{\eta }^{\prime }{K}_S$ modes give results whose central values differ from the SM expectations. We explore the effect of new physics in the two Higgs doublet model (THDM), which allows tree level flavor changing neutral currents (so-called model III), and the model with an extra vectorlike down quark (VLDQ). We find that the observed mixing-induced $\mathrm{CP}$ asymmetry for $\overrightarrow{B}\phi K_S$ cannot be accommodated by the THDM but can be explained in the VLDQ model, and both models can explain the observed asymmetry for $\overrightarrow{B}{\eta }^{\prime }{K}_S$ mode.

We present a general formalism for extracting information on the fundamental parameters associated with neutrino masses and mixings from two or more long baseline neutrino oscillation experiments. This formalism is then applied to the current most likely experiments using neutrino beams from the Japan Hadron Facility (JHF) and Fermilab’s NuMI beamline. Different combinations of muon neutrino or muon anti-neutrino running are considered. The type of neutrino mass hierarchy is extracted using the effects of matter on neutrino propogation. Contrary to naive expectation, we find that both beams using neutrinos is more suitable for determining the hierarchy provided that the neutrino energy divided by baseline $\mathrm{}(E/L)\mathrm{}$ for NuMI is smaller than or equal to that of JHF, whereas to determine the small mixing angle, ${\theta }_{13},$ and the $\mathrm{CP}$ or T violating phase $\delta ,$ one neutrino and the other anti-neutrino are most suitable. We make extensive use of bi-probability diagrams for both understanding and extracting the physics involved in such comparisons.

Using generalized Nielsen identities a formal proof is given that the fermionic quasiparticle dispersion relations in a color superconductor are gauge independent. This turns out to involve gluonic tadpoles which are calculated to one-loop order in a two-flavor color superconductor. Regarding the appearance of gluon tadpoles, we argue that in QCD the color superconducting phase is automatically color neutral.

We perform a linear perturbation analysis for black hole solutions with a “massive” Yang-Mills field (the Proca field) in Brans-Dicke theory and find that the results are quite consistent with those via catastrophe theory where thermodynamic variables play an intrinsic role. Based on this observation, we show the general relation between these two methods in generalized theories of gravity which are conformally related to the Einstein-Hilbert action.

We show that multitrace interactions can be consistently incorporated into an extended AdS conformal field theory (CFT) prescription involving the inclusion of generalized boundary conditions and a modified Legendre transform prescription. We find new and consistent results by considering a self-contained formulation which relates the quantization of the bulk theory to the AdS/CFT correspondence and the perturbation at the boundary by double-trace interactions. We show that there exist particular double-trace perturbations for which irregular modes are allowed to propagate as well as the regular ones. We perform a detailed analysis of many different possible situations, for both minimally and nonminimally coupled cases. In all situations, we make use of a new constraint which is found by requiring consistency. In the particular nonminimally coupled case, the natural extension of the Gibbons-Hawking surface term is generated.

A suggested correspondence between a black hole and a highly excited elementary string is explored. Black hole entropy is calculated by computing the density of states for an open excited string. We identify the square root of the oscillator number of the excited string with the Rindler energy of a black hole to obtain an entropy formula which not only agrees to leading order with the Bekenstein-Hawking entropy, but also reproduces the logarithmic correction obtained for black hole entropy in the quantum geometry framework. This provides additional supporting evidence for the correspondence between black holes and strings.

Mirror matter is a dark matter candidate. In this paper, we reexamine the linear regime of density perturbation growth in a universe containing mirror dark matter. Taking adiabatic scale-invariant perturbations as the input, we confirm that the resulting processed power spectrum is richer than for the more familiar cases of cold, warm and hot dark matter. The new features include a maximum at a certain scale ${\lambda }_{\max },$ collisional damping below a smaller characteristic scale ${\lambda }_S^{\prime },$ with oscillatory perturbations between the two. These scales are functions of the fundamental parameters of the theory. In particular, they decrease for decreasing x, the ratio of the mirror plasma temperature to that of the ordinary. For $x\sim 0.2,$ the scale ${\lambda }_{\max }$ becomes galactic. Mirror dark matter therefore leads to bottom-up large scale structure formation, similar to conventional cold dark matter, for $x\lesssim \mathrm{0.2.}$ Indeed, the smaller the value of x, the closer mirror dark matter resembles standard cold dark matter during the linear regime. The differences pertain to scales smaller than ${\lambda }_S^{\prime }$ in the linear regime, and generally in the nonlinear regime because mirror dark matter is chemically complex and to some extent dissipative. Lyman-α forest data and the early reionization epoch established by WMAP may hold the key to distinguishing mirror dark matter from WIMP-style cold dark matter.

The “central” region of moduli space of M and string theories is where the string coupling is about unity and the volume of compact dimensions is about the string volume. Here we argue that in this region the nonperturbative potential which is suggested by membrane instanton effects has the correct scaling and shape to allow for enough slow-roll inflation and produce the correct amplitude of CMB anisotropies. A limited knowledge of some generic properties of the induced potential is sufficient to determine the simplest type of consistent inflationary model and its predictions about the spectrum of cosmic microwave background anisotropies: a red spectrum of scalar perturbations, and a negligible amount of tensor perturbations.

We investigate whether dark matter with substantial amounts of pressure, comparable in magnitude to the energy density, could be a viable candidate for the constituent of dark matter halos. We find that galaxy halo models, consistent with observations of flat rotation curves, are possible for a variety of equations of state with anisotropic pressures. It turns out that the gravitational bending of light rays passing through such halos is very sensitive to the pressure. We propose that combined observations of rotation curves and gravitational lensing can be used to determine the equation of state of dark matter. Alternatively, if the equation of state is known from other observations, rotation curves and gravitational lensing can together be used to test general relativity on galaxy scales.

We study the implications on both background and perturbation evolution of introducing a Chaplygin gas component in the universe’s ingredients. We perform likelihood analyses using wide-ranging, SN1a, CMB and large scale structure observations to assess whether such a component could be a genuine alternative to a cosmological constant, $\Lambda .$ We find that the current data favors behavior in an adiabatic Chaplygin gas that is akin to a cosmological constant.

We show how the well studied $\gamma \gamma$ inclusive Higgs signal can be used at the CERN Large Hadron Collider to test gauge mediated supersymmetry breaking scenarios in which a rather heavy Higgs boson decays into two light neutralinos, the latter yielding two photons and missing (transverse) energy.

The quark recombination mechanism is proposed to explain the asymmetry between production rates of $D^{+}$ and of $D^{-}$ in their inclusive production, and also asymmetries for other charmed hadrons. These asymmetries are observed in experiment and are called leading particle effects. In this work we give a general analysis for contributions of quark recombination to these asymmetries. The contributions consist of a perturbative and nonperturbative part. We perform two types of factorization by considering the produced hadron with a large transverse momentum and by taking the charm quark as a heavy quark, respectively. In the case of the large transverse momentum the effect of quark recombination is the standard twist-4 effect. We find that the contributions are parametrized with four nonperturbative functions, defined with four quark operators at twist-4, for initial hadrons without polarization. By taking the charm quark as a heavy quark the factorization can be performed with the heavy quark effective theory (HQET). The effect of quark recombination is in general parametrized by eight nonperturbative parameters which are defined as integrals with the matrix elements of four quark operators defined in HQET. For unpolarized hadrons in the initial state, the parameters can effectively be reduced to four. The perturbative parts in the two types of factorization are calculated at the tree level.