We show that the cosmological constant may be reduced by thermal production of membranes by the cosmological horizon, analogous to a particle “going over the top of the potential barrier,” rather than tunneling through it. The membranes are endowed with charge associated with the gauge invariance of an antisymmetric gauge potential. In this new process, the membrane collapses into a black hole; thus, the net effect is to produce black holes out of the vacuum energy associated with the cosmological constant. We study here the corresponding Euclidean configurations (“thermalons”) and calculate the probability for the process in the leading semiclassical approximation.

We investigate the ability to constrain oscillatory features in the primordial power spectrum using current and future cosmic microwave background observations. In particular, we study the observability of an oscillation arising from imprints of physics at the cutoff energy scale. We perform a likelihood analysis on the WMAP data set, and find that the current data set constrains the amplitude of the oscillations to be less than 0.77 at $2\sigma ,$ consistent with a power spectrum without oscillations. In addition, we investigate the fundamental limitations in the measurement of oscillation parameters by studying the constraints from a cosmic variance limited experiment. We find that such an experiment is capable of constraining the amplitude of such oscillations to be below 0.005, implying that reasonable models with cutoff energy scales $\Lambda >{200H}_{\mathrm{infl}}$ are unobservable through the microwave background.

Assuming the equation of state for quintessential matter, $p=w\left(z\right)\mathrm{}\rho ,$ we analyze the dynamical behavior of the scale factor in Friedmann-Robertson-Walker cosmologies. It is shown that its dynamics is formally equivalent to that of a classical particle under the action of a 1D potential $V\left(a\right).$ It is shown that the Hamiltonian method can be easily implemented to obtain a classification of all cosmological solutions in the phase space as well as in the configurational space. Examples taken from modern cosmology illustrate the effectiveness of the approach presented. The advantages of representing dynamics as a 1D Hamiltonian flow, in the analysis of acceleration and standard cosmological problems, are presented. The distant supernovae type Ia data are used to reconstruct the expansion scenario. The inverse problem of reconstructing the Hamiltonian dynamics (i.e., potential function) from the luminosity distance function $d_L\mathrm{}\left(z\right)\mathrm{}$ for supernovae is also considered.

The vacuum expectation value of an operator carrying a magnetic charge is studied numerically for temperatures above the deconfinement temperature in SU(2) and SU(3) gauge theory. By analyzing its finite size behavior, this is found to be exactly zero in the thermodynamical limit for any $T>\mathrm{}{T}_c$ whenever the magnetic charge of the operator is different from zero. These results show that magnetic charge is superselected in the hot phase of quenched QCD.

The universality of single-spin asymmetry in inclusive π-meson production is discussed. This universality can be related to the hadron substructure, constituent quarks.

The SUSY-EW one-loop quantum contributions to flavor-changing MSSM Higgs-boson decays into $b\overline{s}$ and $s\overline{b}$ are computed and discussed. We use the full diagrammatic approach that is valid for all $\tan \beta$ values and do not rely on the mass-insertion approximation for the characteristic flavor-changing parameter. We analyze in full detail the dependence of these flavor-changing partial widths on all the relevant MSSM parameters and also study the nondecoupling behavior of these widths with the SUSY mass parameters. We find that these contributions are sizable as compared to the SM ones, and together with the SUSY-QCD contributions they can be very efficient as an indirect method in the future search for supersymmetry.

In the minimal supersymmetric standard model (MSSM), the masses of the charged Higgs boson ${(H}^{\pm })$ and the CP-odd scalar (A) are related by $M_{H^{+}}^2{=M}_A^2{+m}_W^2$ at the Born level. Because the coupling of $W^{-}-A-H^{+}$ is fixed by the gauge interaction, the Born level production rate of $q{q}^{\prime }\to W^{\pm *}\to {\mathrm{AH}}^{\pm }$ depends on only one supersymmetry parameter—the mass ${(M}_A)$ of A. We examine the sensitivity of the CERN LHC to this signal event in the $A(\to b\overline{b}{)H}^{+}(\to {\tau }^{+}{\nu }_{\tau })$ and $A(\to b\overline{b}{)H}^{+}(\to t\overline{b})$ decay channels. We illustrate how to test the mass relation between A and $H^{+}$ in case the signal is found. If the signal is not found, the product of the decay branching ratios of A and $H^{\pm }$ predicted by the MSSM is bounded from above as a function of $M_A.$

We present the next-to-leading order QCD corrected rate for the production of a scalar Higgs boson with a pair of high $p_T$ bottom and antibottom quarks at the Fermilab Tevatron and at the CERN Large Hadron Collider. Results are given for both the standard model and the minimal supersymmetric standard model. The exclusive $b\overline{b}h$ production rate is small in the standard model, but it can be greatly enhanced in the minimal supersymmetric standard model for large $\tan \beta ,$ making $b\overline{b}h$ an important discovery mode. We find that the next-to-leading order QCD results are much less sensitive to the renormalization and factorization scales than the lowest order results, but have a significant dependence on the choice of the renormalization scheme for the bottom quark Yukawa coupling.

We extend the analysis of two-hadron fragmentation functions to the subleading twist, discussing also the issue of color gauge invariance. Our results can be used anywhere two unpolarized hadrons are semi-inclusively produced in the same fragmentation region, also at moderate values of the hard scale Q. Here, we consider the example of polarized deep-inelastic production of two hadrons and we give a complete list of cross sections and spin asymmetries up to the subleading twist. Among the results, we highlight the possibility of extracting the transversity distribution with longitudinally polarized targets and also the twist-3 distribution $e\left(x\right),$ which is related to the pion-nucleon $\sigma$ term and to the strangeness content of the nucleon.

We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and $\overrightarrow{B}{D}^{**}$ transitions, where $D^{**}$ denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays $B^{-}\to D^{**}{\pi }^{-}$ and $\overrightarrow{B}\overline{D}{D}_s^{**}$ are employed to test the decay constants of $D_s^{**}$ and the $\overrightarrow{B}{D}^{**}$ transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of the IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.

Euclidean space hadronic correlators are computed in quenched QCD at a small quark mass using truncations of quark propagators which include or exclude low eigenvalue eigenmodes of the Dirac operator. High modes provide the dominant contribution to parity averaged correlators, especially at short distances. Differences of correlators of opposite parity receive most of their contributions from low modes and are much smaller in size than parity averages at short distances. The pion propagator in any correlator to which it couples receives a large contribution from low modes, while the tensor meson correlator receives a tiny contribution from low eigenmodes.

We derive a generalized Ward identity for color-superconducting quark matter via the functional integral approach. The identity implies the gauge independence of the color-superconducting gap parameter on the quasiparticle mass shell to subleading order in the covariant gauge.

In $\mathcal{N}=1\mathrm{}$ supersymmetric $\mathrm{SO}\left(N\right)/USp\left(2N\right)\mathrm{}$ gauge theories with the tree-level superpotential $W\left(\Phi \right)$ that is an arbitrary polynomial of the adjoint matter $\Phi ,$ the massless fluctuations about each quantum vacuum are described by ${U\left(1\right)\mathrm{}}^n$ gauge theory. By turning on the parameters of $W\left(\Phi \right)$ to the special values, the singular vacua where the additional fields become massless can be reached. Using the matrix model prescription, we study the intersections of $n=0\mathrm{}$ and $n=1\mathrm{}$ branches. The general formula for the matrix model curve at the singularity which is valid for arbitrary N is obtained and this generalizes the previous results for small values of N from the strong-coupling approach. Applying the analysis to the degenerated case, we also obtain a general matrix model curve which is not only valid at a special point but also on the whole branch.

In four-dimensional general relativity, the fact that a Killing vector in a vacuum spacetime serves as a vector potential for a test Maxwell field provides one with an elegant way of describing the behavior of electromagnetic fields near a rotating Kerr black hole immersed in a uniform magnetic field. We use a similar approach to examine the case of a five-dimensional rotating black hole placed in a uniform magnetic field of configuration with biazimuthal symmetry that is aligned with the angular momenta of the Myers-Perry spacetime. Assuming that the black hole may also possess a small electric charge we construct the five-vector potential of the electromagnetic field in the Myers-Perry metric using its three commuting Killing vector fields. We show that, like its four-dimensional counterparts, the five-dimensional Myers-Perry black hole rotating in a uniform magnetic field produces an inductive potential difference between the event horizon and an infinitely distant surface. This potential difference is determined by a superposition of two independent Coulomb fields consistent with the two angular momenta of the black hole and two nonvanishing components of the magnetic field. We also show that a weakly charged rotating black hole in five dimensions possesses two independent magnetic dipole moments specified in terms of its electric charge, mass, and angular momentum parameters. We prove that a five-dimensional weakly charged Myers-Perry black hole must have the value of the gyromagnetic ratio $g=3.\mathrm{}$

We discuss the entropy change due to fragmentation for black hole solutions in various dimensions. We find three different types of behavior. The entropy may decrease, increase, or have a mixed behavior, characterized by the presence of a threshold mass. For two-dimensional (2D) black holes we give a complete characterization of the entropy behavior under fragmentation, in the form of sufficient conditions imposed on the function J, which defines the 2D gravitational model. We compare the behavior of the gravitational solutions with that of free field theories in d dimensions. This excludes for a broad class of solutions, including asymptotically flat black holes, the possibility of finding a duality between gravity and a field theory, which realizes the holographic principle. We find that the most natural candidates for holographic duals of the black hole solutions with mixed behavior are field theories with a mass gap. We also discuss the possibility of formulating entropy bounds that make reference only to the energy of a system.

A phenomenological approach is proposed to the problem of the accelerated expansion of the Universe and of the nature of dark energy. A general class of models is introduced whose energy density depends on the redshift z in such a way that a smooth transition among the three main phases of the evolution of the Universe (radiation era, matter domination, asymptotical de Sitter state) is naturally achieved. We use the estimated age of the Universe, the Hubble diagram of type-Ia supernovae, and the angular size–redshift relation for compact and ultracompact radio structures, to test whether the model is in agreement with astrophysical observation and to constrain its main parameters. Although phenomenologically motivated, the model may be straightforwardly interpreted as a two-fluid scenario in which the quintessence is generated by a suitably chosen scalar field potential. On the other hand, the same model may also be read in the context of unified dark energy models or in the framework of modified Friedmann equation theories.

The evolution of two slow-rolling scalar fields with potentials of the form ${V=V}_0{\phi }^{-\alpha }\exp \left(-\beta {\phi }^m\right)$ is studied. Considering different values of the parameters $\alpha ,$ $\beta$ and m, we derive several new inflationary solutions in which one field just evolves in the background and is not important for the inflationary dynamics. In addition, we find new solutions where both fields are dynamically important during inflation. Moreover, we discuss the evolution of perturbations in both scalar fields and the spacetime metric, concentrating on the production of entropy perturbations. We find that for a large region in parameter space and initial conditions tensor modes are negligible and that adiabatic and isocurvature perturbations are essentially uncorrelated.

By introducing local $Z_N$ symmetries with $N=11,13\mathrm{}$ in two 3-3-1 models, it is possible to implement an automatic Peccei-Quinn symmetry, keeping the axion protected against gravitational effects at the same time. Both models have a $Z_2$ domain wall problem and the neutrinos are strictly Dirac particles.

We consider a nonuniversal five-dimensional model in which fermions are localized on a four-dimensional brane, while gauge bosons and a scalar doublet can travel in the bulk. As a result of Kaluza-Klein number nonconservation at the brane-bulk intersection, the ultraviolet divergence does not cancel out in some physical observables. For example, the $B_d\to {\mathcal{l}}^{+}{\mathcal{l}}^{-}$ decay amplitude is linearly divergent, while the $B-\overline{B}$ mixing amplitude is log divergent. We attempt to identify the exact source of this nonrenormalizability. We compare and contrast our results with those obtained in the universal five-dimensional model where all particles travel in the extra dimension.

A complete one-loop computation of the processes $({\tilde{\chi }}_i^0{\tilde{\chi }}_j^0\leftrightarrow \gamma \gamma ,gg),$ for any pair of the four minimal supersymmetric standard model (MSSM) neutralinos, has been performed for an arbitrary c.m. energy. As a first application suitable for dark matter (DM) searches neutralino-neutralino annihilation is studied at relative velocities $v/c\simeq {10}^{-3},$ describing the present DM distribution in the galactic halo, and $v/c\simeq 0.5,$ determining neutralino relic density contributions. Numerical results are presented for 31 MSSM benchmark models indicating considerable sensitivity to the input parameters. Numerical codes are released, which may be used for the computation of the annihilation of any two neutralinos to two photons or two gluons at the aforementioned $v/c$ values. In the near future, we intend to complement them with codes for the inverse process $\gamma \overrightarrow{\gamma }{\tilde{\chi }}_i^0{\tilde{\chi }}_j^0,$ observable at future high energy linear colliders.