We propose a new mechanism to generate density perturbations in inflationary models. Spatial fluctuations in the decay rate of the inflaton field to ordinary matter lead to fluctuations in the reheating temperature. We argue that in most realistic models of inflation the coupling of the inflaton to normal matter is determined by the vacuum expectation values of fields in the theory. If those fields are light during inflation (this is a generic situation in the minimal models of supersymmetric inflation) they will fluctuate leading to density perturbations through the proposed mechanism. We show that these fluctuations could easily dominate over the ones generated through the standard mechanism. The new scenario has several consequences for inflation model building and observations. The proposed mechanism allows us to generate the observed level of density perturbations with a much lower scale of inflation and thus generically predicts a smaller level of gravitational waves. The relation between the slope of the spectrum of the produced density perturbations and the potential of the inflaton field is different from the standard relations obtained in the context of slow roll inflation. Because the field responsible for the fluctuations is not the inflaton, it can have significantly larger self-couplings and thus density perturbations could be non-Gaussian. The non-Gaussianity can be large enough to be detectable by CMB and large scale structure observations.

We study in the quasiclassical approximation the radiation reaction and its influence on the space-time evolution for the small relativistic dipole moving in a constant external electromagnetic field in QED.

We study fermion masses and mixing angles, including the generation of a seesaw mechanism for the neutrinos, in extended technicolor (ETC) theories. We formulate an approach to these problems that relies on assigning right-handed $Q=-1/3$ quarks and charged leptons to ETC representations that are conjugates of those of the corresponding left-handed fermions. This leads to a natural suppression of these masses relative to the $Q=2/3\mathrm{}$ quarks, as well as the generation of quark mixing angles, both long-standing challenges for ETC theories. Standard-model-singlet neutrinos are assigned to ETC representations that provide a similar suppression of neutrino Dirac masses, as well as the possibility of a realistic seesaw mechanism with no mass scale above the highest ETC scale of roughly ${10}^3\mathrm{TeV}.$ A simple model based on the ETC group SU(5) is constructed and analyzed. This model leads to nontrivial, but not realistic mixing angles in the quark and lepton sectors. It can also produce sufficiently light neutrinos, although not simultaneously with a realistic quark spectrum. We discuss several aspects of the phenomenology of this class of models.

We examine the phenomenological consequences of a supersymmetric bulk in the scenario of large extra dimensions. We assume that supersymmetry is realized in the bulk and study the interactions of the resulting bulk gravitino Kaluza-Klein (KK) tower of states, with supersymmetry breaking on the brane inducing a light mass for the zero-mode gravitino. We derive the 4D effective theory, including the couplings of the bulk gravitino KK states to fermions and their scalar superpartners. The virtual exchange of the gravitino KK states in selectron pair production in polarized $e^{+}{e}^{-}$ collisions is then examined. We find that the leading order operator for this exchange is dimension 6, in contrast with that of bulk graviton KK exchange which induces a dimension 8 operator at lowest order. The resulting kinematic distributions for selectron production are dramatically altered from those in $D=4\mathrm{}$ supersymmetric scenarios and can lead to an enormous sensitivity to the fundamental higher-dimensional Planck scale, of order $(20\mathrm{}–25)\times \sqrt{s}.$

The chiral nonanalytic behavior of quark-flavor contributions to the magnetic moments of octet baryons is determined in full, quenched and partially quenched QCD, using an intuitive and efficient diagrammatic formulation of quenched and partially quenched chiral perturbation theory. The technique provides a separation of quark-sector magnetic-moment contributions into direct sea-quark loop, valence-quark, indirect sea-quark loop and quenched valence contributions, the latter being the conventional view of the quenched approximation. Both meson and baryon mass violations of $\mathrm{SU}\left(3\right)\mathrm{}$-flavor symmetry are accounted for. Following a comprehensive examination of the individual quark-sector contributions to octet baryon magnetic moments, numerous opportunities to observe and test the underlying structure of baryons and the nature of chiral nonanalytic behavior in QCD and its quenched variants are discussed. In particular, the valence u-quark contribution to the proton magnetic moment provides the optimal opportunity to directly view nonanalytic behavior associated with the meson cloud of full QCD and the quenched meson cloud of quenched QCD. The u quark in ${\Sigma }^{+}$ provides the best opportunity to display the artifacts of the quenched approximation.

We have measured the number of like-sign (LS) and opposite-sign (OS) lepton pairs arising from double semileptonic decays of b and $\overline{b}$ hadrons, pair produced at the Fermilab Tevatron collider. The data samples were collected with the Collider Detector at Fermilab during the 1992–1995 collider run by triggering on the existence of $\mu \mu$ or $e\mu$ candidates in an event. The observed ratio of LS to OS dileptons leads to a measurement of the average time-integrated mixing probability of all produced b-flavored hadrons which decay weakly, $\overline{\chi }=0.152\mathrm{}\pm 0.007\left(\mathrm{stat}\right)\pm 0.011\left(\mathrm{syst}\right),$ that is significantly larger than the world average $\overline{\chi }=0.118\mathrm{}\pm \mathrm{0.005.}$

We construct a sequence of binary black hole puncture data derived under the assumptions (i) that the Arnowitt-Deser-Misner (ADM) mass of each puncture as measured in the asymptotically flat space at the puncture stays constant along the sequence, and (ii) that the orbits along the sequence are quasicircular in the sense that several necessary conditions for the existence of a helical Killing vector are satisfied. These conditions are the equality of the ADM and Komar mass at infinity and the equality of the ADM and a rescaled Komar mass at each puncture. In this paper we explicitly give results for the case of an equal mass black hole binary without spin, but our approach can also be applied in the general case. We find that up to numerical accuracy the apparent horizon mass also remains constant along the sequence and that the prediction for the innermost stable circular orbit is similar to what has been found with the effective potential method.

We study how the angular resolution of the Laser Interferometer Space Antenna for merging massive black-hole binaries would be improved if we observe multiple gravitational wave “images” due to strong gravitational lensing. The correlation between fitting parameters is reduced by the additional information of the second image which significantly reduces the error box on the sky. This improvement would be very helpful for identifying the host galaxy of a binary. The angular resolution expected with multiple detectors is also discussed.

We present a variational method which uses a quartic exponential function as a trial wave function to describe time-dependent quantum mechanical systems. We introduce a new physical variable y which is appropriate to describe the shape of a wave packet, and calculate the effective action as a function of both the dispersion $\sqrt{〈q^2〉}$ and y. The effective potential successfully describes the transition of the system from the false vacuum to the true vacuum. The present method well describes the time evolution of the wave function of the system for a short period for the quantum roll problem and describes the long-time evolution up to 75% accuracy. These are shown in comparison with direct numerical computations of the wave function. We briefly discuss the large N behavior of the present approximation.

This is the fourth paper in a series devoted to a systematic study of the problem of a mathematically correct formulation of the rules needed to manage an effective field theory. Here we consider the problem of constructing the full set of essential parameters in the case of the most general effective scattering theory containing no massless particles with spin $J>\mathrm{}1/2.\mathrm{}$ We perform a detailed classification of combinations of the Hamiltonian coupling constants and select those which appear in the expressions for renormalized S-matrix elements at a given loop order.

The role of the measurement process in resolving the gauge ambiguity of the effective gravitational potential is reexamined. The motion of a classical pointlike particle in the field of an arbitrary linear source and in the field of another pointlike particle is investigated. It is shown that in both cases the value of the gravitational field read off from the one-loop effective action of the testing particle depends on the Feynman weighting parameter. The found dependence is essential in that it persists in the expression for the gravitational potential. This result disproves the general conjecture about the gauge independence of the effective equations of motion of classical pointlike particles.

Motivated by the study of quantum fields in a Friedmann-Robertson-Walker space-time, the one-loop effective action for a scalar field defined in the ultrastatic manifold $R\times H^3/\Gamma ,$ $H^3/\Gamma$ being the finite volume, noncompact, hyperbolic spatial section, is investigated by a generalization of zeta-function regularization. It is shown that additional divergences may appear at the one-loop level. The one-loop renormalizability of the model is discussed and, making use of a generalization of zeta-function regularization, the one-loop renormalization group equations are derived.

We study the onset of symmetry breaking after hybrid inflation in a model having the field content of the SU(2) gauge-scalar sector of the standard model, coupled to a singlet inflaton. This process is studied in 3+1 dimensions in a fully nonperturbative way with the help of lattice techniques within the classical approximation. We focus on the role played by gauge fields and, in particular, on the generation of Chern-Simons number. Our results are shown to be insensitive to the various cutoffs introduced in our numerical approach. The spectra preserves a large hierarchy between long- and short-wavelength modes during the whole period of symmetry breaking and Chern-Simons generation, confirming that the dynamics is driven by the low momentum sector of the theory. We establish that the Chern-Simons production mechanism is associated with local sphaleronlike structures. The corresponding sphaleron rates are of order ${10}^{-5}{m}^4,$ which, within certain scenarios of electroweak baryogenesis and a (not unnaturally large) additional source of CP violation, could explain the present baryon asymmetry of the Universe.

Long-range quasistatic gauge-boson interactions lead to anomalous (non-Fermi-liquid) behavior of the specific heat in the low-temperature limit of an electron or quark gas with a leading $T\ln T^{-1}$ term. We obtain perturbative results beyond the leading log approximation and find that dynamical screening gives rise to a low-temperature series involving also anomalous fractional powers $T^{\mathrm{}(3+2n)/3\mathrm{}}.$ We determine their coefficients in perturbation theory up to and including order $T^{7/3}$ and compare with exact numerical results obtained in the large-$N_f$ limit of QED and QCD.

Using data on $K^{+}$ collisions on xenon and deuterium we derive values and limits on the width of the reported $\Theta {\mathrm{}\left(1540\right)\mathrm{}}^{+}$ exotic baryon resonance. The xenon experiment gives a width of $0.9\pm 0.3\mathrm{MeV}.$ The other experiments give upper limits in the range 1–4 MeV.

The perturbative vacuum of type 0 string theory is unstable due to the existence of the closed string tachyon. This instability can be removed by ${\mathbf{S}}^1$ compactification with the twisted boundary condition for the tachyon field. We show that even in this situation unwrapped NS5-branes are unstable and decay to bubbles of nothing smoothly without tunneling any potential barrier. We discuss a relation between the closed string tachyon condensation and the instability of NS5-branes.

A new solution to the Einstein equations in $1+5$ spacetime with an embedded $1+3$ brane is given. This solution localizes the zero modes of all kinds of matter fields and four-gravity on the (1+3) brane by an increasing, transverse gravitational potential. This localization occurs despite the fact that the gravitational potential is not a decreasing exponential, and asymptotically approaches a finite value rather than zero.

The Gliozzi-Scherk-Olive (GSO) projection in the twisted sector of an orbifold background is sometimes subtle, and incompatible descriptions are found in the literature. Here, from the equivalence of partition functions in Neveu-Schwarz-Ramond and Green-Schwarz formalisms, we give a simple rule of the GSO projection for the chiral rings of string theory in $C^3/Z_n.$ The necessary constructions of chiral rings are given by explicit mode analysis.