A new physical mechanism is suggested to explain the universal depletion of high meson excitations. It takes into account the appearance of holes inside the string world sheet due to $q\overline{q}$ pair creation when the length of the string exceeds the critical value $R_1\simeq 1.4\hspace{0.5em}\mathrm{fm}$. It is argued that a delicate balance between large $N_c$ loop suppression and a favorable gain in the action, produced by holes, creates a new metastable (predecay) stage with a renormalized string tension which now depends on the separation r. This results in smaller values of the slope of the radial Regge trajectories, in good agreement with the analysis of experimental data of Anisovich, Anisovich, and Sarantsev.

In the framework of the QCD string approach it is shown that the spin-averaged masses $\overline{M}\mathrm{}\left(\mathrm{nL}\right)\mathrm{}$ of all low-lying light mesons are well described using the string tension $\sigma$ as the only parameter. The Regge slope ${\alpha }_L^{\prime }$ and the intercept ${\alpha }_L\mathrm{}\left(0\right)\mathrm{}$ of the Regge L trajectory for $\overline{M}\mathrm{}\left(\mathrm{nL}\right)\mathrm{}$ are calculated analytically and turn out to be ${\alpha }_L^{\prime }=0.80\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^{-2}$ (for $L<~4)$ and ${\alpha }_L\mathrm{}\left(0\right)=-0.34,$ in good agreement with the experimental data: ${\alpha }_{L\mathrm{expt}}^{\prime }=0.81\mathrm{}\pm 0.01\hspace{0.5em}{\mathrm{GeV}}^{-2},$ ${\alpha }_{L\mathrm{expt}}\mathrm{}\left(0\right)=-0.30\pm \mathrm{0.02.}$ To obtain this strong agreement with the data the nonperturbative quark self-energy contributions to the meson masses must be taken into account, which appear to be large and negative for small values of L, and are important for a close fit even for larger values of L. From the present analysis of the meson spectra the restriction ${\alpha }_s<~0.40$ on the strong coupling constant is required.

We argue that the t dependence of the two-gluon form factor of the nucleon should be given by $\Gamma \mathrm{}\left(t\right)=(1\mathrm{}-{t/m}_{2g}^2{)}^{-2}$ with $m_{2g}^2\approx 1\hspace{0.5em}{\mathrm{GeV}}^2.$ We demonstrate that this form provides a good description of the t dependence of the cross section of the elastic photoproduction of $J/\psi$ mesons between the threshold region of $E_{\gamma }=11\mathrm{}\hspace{0.5em}\mathrm{GeV}$ (Cornell), $E_{\gamma }=19\mathrm{}\hspace{0.5em}\mathrm{GeV}$ (SLAC) and $E_{\gamma }=100\mathrm{}\hspace{0.5em}\mathrm{GeV}$ (Fermilab), including the strong energy dependence of the t slope. It is also well matched with the recent DESY HERA data. The same assumption explains also the t dependence of φ-meson electroproduction near threshold at $W=2.3\mathrm{}\hspace{0.5em}\mathrm{GeV},$ $Q^2=1.0\mathrm{}\hspace{0.5em}{\mathrm{GeV}}^2.$

We reconsider several current bounds on the variation of the fine-structure constant in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories. In particular, we reexamine the bounds established by the Oklo reactor from the resonant neutron capture cross section of ${}^{149}\mathrm{Sm}.$ By imposing variations in ${\Lambda }_{\mathrm{QCD}}$ and the quark masses, as dictated by unified theories, the corresponding bound on the variation of the fine-structure constant can be improved by about 2 orders of magnitude in such theories. In addition, we consider possible bounds on variations due to their effect on long lived α- and β-decay isotopes, particularly ${}^{147}\mathrm{Sm}$ and ${}^{187}\mathrm{Re}.$ We obtain a strong constraint on $\Delta \alpha /\alpha ,$ comparable to that of Oklo but extending to a higher redshift corresponding to the age of the solar system, from the radioactive lifetime of ${}^{187}\mathrm{Re}$ derived from meteoritic studies. We also analyze the astrophysical consequences of perturbing the decay Q values on bound state β decays operating in the s process.

We compute the nonholomorphic corrections to the low-energy effective action (higher derivative terms) in $\mathcal{N}=2,\hspace{0.5em}\hspace{0.5em}\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}$ super Yang-Mills theory coupled to hypermultiplets on a non-Abelian background for a class of gauge fixing conditions. A general procedure for calculating the gauge parameter dependent contributions to the one-loop superfield effective action is developed. The one-loop nonholomorphic effective potential is exactly found in terms of the Euler dilogarithm function for a specific choice of gauge parameters.

We consider the most general parametrization of flat topologically compact universes, complementing the work of Scannapieco, Levin and Silk to include nontrivial shapes. We find that modifications in the shape of the fundamental domain will lead to distinct signatures in the anisotropy of the cosmic microwave radiation. We make a preliminary assessment of the effect on three statistics: the angular power spectrum, the distribution of identified “circles” on the surface of last scattering and the correlation function of antipodal points.

Recently a new class of composite Higgs models have been developed which give rise to naturally light Higgs bosons without supersymmetry. Based on the chiral symmetries of “theory space,” involving replicated gauge groups and appropriate gauge symmetry breaking patterns, these models allow the scale of the underlying strong dynamics giving rise to the composite particles to be as large as of order 10 TeV, without any fine tuning to prevent large corrections to Higgs boson mass(es) of order 100 GeV. In this paper we show that the size of flavor violating interactions arising generically from underlying flavor dynamics constrains the scale of the Higgs boson compositeness to be greater than of order 75 TeV, implying that significant fine-tuning is required. Without fine-tuning, the low-energy structure of the composite Higgs model alone is not sufficient to eliminate potential problems with flavor-changing neutral currents or excessive $\mathrm{CP}$ violation; solving those problems requires additional information or assumptions about the symmetries of the underlying flavor or strong dynamics. We also consider the weaker, but more model-independent, bounds which arise from limits on weak isospin violation.

We reexamine the possibility that the solution to the supersymmetric flavor problem is related to small mixing angles in gaugino couplings induced by approximate horizontal Abelian symmetries. We prove that, for a large class of models, there is a single viable structure for the down quark mass matrix with four holomorphic zeros. Consequently, we are able to obtain both lower and upper bounds on the supersymmetric mixing angles and predict the contributions to various flavor changing neutral current processes. We find that the most likely signals for alignment are $\Delta m_D$ close to the present bound, significant $\mathrm{CP}$ violation in $D^0-\overline{D^0}$ mixing, and shifts of the order of a few percent in various $\mathrm{CP}$ asymmetries in $B^0$ and $B_s$ decays. In contrast, the modifications to radiative B decays, to ${\varepsilon }^{\prime }/\varepsilon$ and to $\overrightarrow{K}\pi \nu \overline{\nu }$ decays are small. We further investigate a new class of alignment models, where supersymmetric contributions to flavor changing processes are suppressed by both alignment and RGE-induced degeneracy.

Flat manifold leptogenesis in the manner of Affleck and Dine is investigated with the slepton and Higgs fields, $\tilde{L},$ $H_u,$ $H_d,$ in the supersymmetric standard model. The multidimensional motion of these scalar fields is realized in the case that the $\tilde{L}{H}_u$ and $H_u{H}_d$ directions are comparably flat with the relevant nonrenormalizable superpotential terms. Soon after inflation, lepton number asymmetry appears to fluctuate due to this multidimensional motion involving certain $\mathrm{CP}$ violating phases. Then, it is fixed to some significant nonzero value for the successful baryogenesis when the scalar fields begin to oscillate with rotating phases driven by the quartic coupling from the superpotential term $h_e{\mathrm{LH}}_d{e}^c$ with $h_e\sim {10}^{-5}–{10}^{-3}.$ The Hubble parameter $H_{\mathrm{osc}}$ at this epoch for the completion of leptogenesis is much larger than the gravitino mass $m_{3/2}\sim {10}^3\hspace{0.5em}\mathrm{GeV}.$ The thermal terms may even play a cooperative role in this scenario of early leptogenesis. The lightest neutrino mass can be $m_{{\nu }_1}\sim {10}^{-4}$ eV, if the reheating temperature is allowed to be $T_R\sim {10}^{10}$ GeV.

We construct a left-right symmetric model based on the gauge group ${\mathrm{SU}\left(2\right)\mathrm{}}_L\times {\mathrm{SU}\left(2\right)\mathrm{}}_R\times {U\left(1\right)\mathrm{}}_{B-L}$ in five dimensions where both the gauge bosons and fermions reside in all five dimensions. The orbifold boundary conditions are used not only to break the gauge symmetry down to ${\mathrm{SU}\left(2\right)\mathrm{}}_L\times {U\left(1\right)\mathrm{}}_Y\times {U\left(1\right)\mathrm{}}_{Y^{\prime }}$ but also to “project” the right handed neutrino out of the zero mode part of the spectrum, providing a new way to understand the small neutrino masses without adding (singlet) bulk neutrinos. This formulation of the left-right model also has two new features: (i) it avoids most existing phenomenological bounds on the scale of the right handed $W_R$ boson allowing for the possibility that the right handed gauge bosons could have masses under a TeV, and (ii) it predicts a stable lepton with mass of order of the inverse radius of the fifth dimension.

We investigate single sneutrino production in the context of R-parity-violating supersymmetry at future $\gamma \gamma$ linear colliders. The sneutrino is produced in association with fermion pairs and it is shown that its decays into two further fermions will lead to a clean signal. We also discuss possible standard model backgrounds and the effects of beam polarization.

The observation of the ${\overline{\nu }}_e$ energy spectrum from a supernova burst can provide constraints on neutrino oscillations. We derive formulas for adiabatic oscillations of supernova antineutrinos for a variety of 3- and 4-neutrino mixing schemes and mass hierarchies which are consistent with the Liquid Scintillation Neutrino Detector (LSND) evidence for ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ oscillations. Finally, we explore the constraints on these models and LSND given by the supernova SN 1987A ${\overline{\nu }}_e’\mathrm{s}$ observed by the Kamiokande-2 and IMB-3 detectors.

We study the renormalization of the llHH-type Majorana neutrino mass operator in a scenario in which there is a compactified extra dimension and the fields involved correspond to only the standard model particles and their Kaluza-Klein excitations. We observe that in a two-flavor scenario, in which one of the neutrinos is necessarily ${\nu }_{\tau },$ it is indeed possible to generate a large mixing at $\sim 100\mathrm{GeV}$ starting from a very small mixing near the ultraviolet cutoff $\sim 30\mathrm{TeV}.$ In passing, we also derive the Higgs mass upper and lower limits from perturbative unitarity and stability of the potential, respectively.

A search for nearly vertical up-going muon-neutrinos from neutralino annihilations in the center of the Earth has been performed with the AMANDA-B10 neutrino detector. The data collected in 130.1 days of live time in 1997, $\sim {10}^9$ events, have been analyzed for this search. No excess over the expected atmospheric neutrino background has been observed. An upper limit at 90% confidence level has been obtained on the annihilation rate of neutralinos in the center of the Earth, as well as the corresponding muon flux limit, both as a function of the neutralino mass in the range 100 GeV–5000 GeV.

We examine a bilinear form Wess-Zumino term for a superstring in anti–de Sitter (AdS) spaces. This is composed of two parts: a bilinear term in superinvariant currents and a total derivative bilinear term which is required for the pseudosuperinvariance of the Wess-Zumino term. The covariant supercharge commutator containing a string charge is also obtained.

We find the perturbation spectrum of a family of spherically symmetric and continuously self-similar (CSS) exact solutions that appear to be relevant for the critical collapse of scalar field matter in $2+1$ spacetime dimensions. The rate of exponential growth of the unstable perturbation yields the critical exponent. Our results are compared to the numerical simulations of Pretorius and Choptuik and are inconclusive: We find a CSS solution with exactly one unstable mode, which suggests that it may be the critical solution, but another CSS solution which has three unstable modes fits the numerically found critical solution better.

We consider nonlinear gravitational models with a multidimensional warped product geometry. Particular attention is payed to models with quadratic scalar curvature terms. It is shown that for certain parameter ranges, the extra dimensions are stabilized if the internal spaces have a negative constant curvature. In this case, the four-dimensional effective cosmological constant as well as the bulk cosmological constant become negative. As a consequence, the homogeneous and isotropic external space is asymptotically ${\mathrm{AdS}}_4.$ The connection between the D-dimensional and the four-dimensional fundamental mass scales sets a restriction on the parameters of the considered nonlinear models.

Using the 3+1 formalism of general relativity the equations governing the dynamics of spherically symmetric spacetimes with arbitrary sources are obtained. The case of a perfect fluid accompanied by a flow of interacting massless or massive particles (e.g., neutrinos) which are described in terms of relativistic transport theory is then specialized. I focus on three types of gauges: (1) the isotropic-maximal gauge, (2) radial-polar gauge, and (3) isotropic-polar gauge.

Inflation ends with the formation of a Bose condensate of inflatons. We show that in hybrid inflation models this condensate is typically unstable with respect to spatial perturbations and can fragment to condensate lumps. The case of D-term inflation is considered as an example and it is shown that fragmentation occurs if $\lambda \gtrsim 0.2g,$ where $\lambda$ is the superpotential coupling and g is the ${U\left(1\right)\mathrm{}}_{\mathrm{FI}}$ gauge coupling. Condensate fragmentation can result in an effective enhancement of inflaton annihilations over decays as the main mode of reheating. In the case of D-term inflation models in which the standard model fields carry ${U\left(1\right)\mathrm{}}_{\mathrm{FI}}$ charges, if condensate fragmentation occurs then reheating is dominated by inflaton annihilations, typically resulting in the overproduction of thermal gravitinos. Fragmentation may also have important consequences for SUSY flat direction dynamics and for preheating.

We analyze the mechanism of quintessential inflation in brane world scenarios for a number of particle physics inspired scalar potentials. We constrain the parameter space of those scalar potentials and comment on the likelihood that we could discriminate these models from standard inflation, based on upcoming large scale structure and cosmic microwave background observations.