We use the $\delta N$ formalism to describe the leading order contributions to the primordial power spectrum, bispectrum, and trispectrum in multiple-field models of inflation at leading order in a perturbative expansion. In slow-roll models where the initial field fluctuations at Hubble exit are nearly Gaussian, any detectable non-Gaussianity is expected to come from super-Hubble evolution. We show that the contribution to the primordial trispectrum can be described by two nonlinearity parameters, ${\tau }_{NL}$ and $g_{NL}$, which are dependent upon the second and third derivatives of the local expansion with respect to the field values during inflation.

In a cold dark matter (CDM) paradigm, density perturbations enter the nonlinear regime of structure formation where shell crossings occur, and caustics form. A dark matter caustic is generically a surface in space where the CDM particles are naturally focussed, and hence, the density is very large. The caustic ring model of galactic halo formation predicts a minimal caustic structure classified as outer caustics and caustic rings at certain locations in the halos. It provides a well-defined density profile and geometry near the caustics. Using this model, I show that the gravitational lensing by the cusps ($A_{-3}$ catastrophes) of caustic rings at cosmological distances may offer the tantalizing opportunity to detect CDM indirectly, and discriminate between axions and weakly interacting massive particles (WIMPs). The lensing effects of the caustic rings increase as the line of sight approaches to the cusps where it diverges in the limit of zero velocity dispersion. In the presence of finite velocity dispersion, the caustics are smeared out in space, and hence, the divergence is cut off. Primordial smearing distance of caustics may be used to obtain an upper bound for the lensing effects. Evidences found for the caustic rings, on the other hand, were used to estimate an upper bound for the smearing distance, which may be used to obtain a lower bound for the lensing effects. In that range of smearing out, the magnification of a cosmological axion caustic ring is constrained between 3% and 2800% at the outer cusp, and between 2% and 46% at the nonplanar cusps. For a cosmological WIMP caustic ring, the magnification is constrained between 3% and 28% at the outer cusp, and between 2% and 5% at the nonplanar cusps. As pointlike background sources cross behind the axion (WIMP) folds, the time scale of brightness change is about an hour (a year). Thus, they may be used to probe the cusps and discriminate between axions and WIMPs by present instruments. Finally, I derive and analyze the catastrophe function of the triaxial caustic rings to prove rigorously that they are structurally stable.

We present an explicit on-shell framework to renormalize the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix at the one-loop level. It is based on a novel procedure to separate the external-leg mixing corrections into gauge-independent self-mass (sm) and gauge-dependent wave-function renormalization contributions, and to adjust nondiagonal mass counterterm matrices to cancel all the divergent sm contributions, and also their finite parts subject to constraints imposed by the Hermiticity of the mass matrices. It is also shown that the proof of gauge independence and finiteness of the remaining one-loop corrections to $W\to q_i+{\overline{q}}_j$ reduces to that in the unmixed, single-generation case. Diagonalization of the complete mass matrices leads then to an explicit expression for the CKM counterterm matrix, which is gauge independent, preserves unitarity, and leads to renormalized amplitudes that are nonsingular in the limit in which any two fermions become mass degenerate.

We examine the sensitivity of $e\gamma$ colliders (based on $e^{+}{e}^{-}$ linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to W-boson via the process $e^{-}\gamma ⟶\nu WH$. This has the advantage over $e^{+}{e}^{-}$ collider in being able to dissociate $WWH$ vertex from $ZZH$. We are able to construct several dynamical variables which may be used to constrain the various couplings in the $WWH$ vertex.

The contributions of the neutral top-pion ${\pi }_t^0$ and the nonuniversal gauge boson $Z^{\prime }$ predicted by the topcolor scenario to the lepton flavor violating semileptonic $\tau$ decays $\tau \to lP(V)$ ($P={\pi }^0$, $\eta$, ${\eta }^{\prime }$ and $V={\rho }^0$, $\varphi$) are discussed. We find that the contributions of $Z^{\prime }$ to these decay processes are generally larger than those from ${\pi }_t^0$. ${\pi }_t^0$ can only make the value of the branching ratio $\mathrm{Br}(\tau \to lP)$ in the range of $1\times {10}^{-11}–1\times {10}^{-16}$, which is far below the sensitivity of foreseeable experiments. With reasonable values of the free parameters, the nonuniversal gauge boson $Z^{\prime }$ can make the value of the branching ratio $\mathrm{Br}({\tau }^{-}\to {\mu }^{-}\varphi )$ reach $1\times {10}^{-7}$, which might approach the observable threshold of near-future experiments.

Intersecting $D$-brane theories motivate the existence of exotic $U(1)$ gauge bosons that only interact with the standard model through kinetic mixing with hypercharge. We analyze an effective field theory description of this effect and describe the implications of these exotic gauge bosons on precision electroweak, LHC, and ILC observables.

Growing evidence indicates that in the continuum limit the rooted staggered action is in the correct QCD universality class, the nonlocal terms arising from taste breaking can be viewed as lattice artifacts. In this paper we consider the 2-flavor Asqtad staggered action at lattice spacing $a\approx 0.13\mathrm{fm}$ and probe the properties of the staggered configurations by an overlap valence Dirac operator. By comparing the distribution of the overlap eigenmodes to continuum QCD predictions we investigate if/when the lattice artifacts are small as a function of the staggered quark mass. We define a matching overlap quark mass where the lattice corrections are minimal for the topological susceptibility and from the eigenmode distribution we predict the 2-flavor chiral condensate. Our results indicate that the staggered configurations are consistent with 2-flavor continuum QCD up to small lattice artifacts, and predict a consistent value for the infinite volume chiral condensate.

It has been suggested in Ref. [A. E. Bondar and V. L. Chernyak, Phys. Lett. B 612, 215 (2005)] that the disagreement between theoretical calculations and experimental observations for the rate for the process $e^{+}{e}^{-}\to J/\psi +{\eta }_c$ at the $B$ factories might be resolved by using the light-cone method to take into account the relative momentum of the heavy-quark and antiquark in the quarkonia. The light-cone result for the production cross section in Ref. [A. E. Bondar and V. L. Chernyak, Phys. Lett. B 612, 215 (2005)] is almost an order-of-magnitude larger than existing NRQCD factorization results. We investigate this apparent theoretical discrepancy. We compute light-cone distribution functions by making use of quarkonium wave functions from the Cornell potential model. Our light-cone distribution functions are similar in shape to those of Ref. [A. E. Bondar and V. L. Chernyak, Phys. Lett. B 612, 215 (2005)] and yield a similar cross section. However, when we subtract parts of the light-cone distribution functions that correspond to corrections of relative-order ${\alpha }_s$ in the NRQCD approach, we find that the cross section decreases by about a factor of three. When we set certain renormalization factors $Z_i$ in the light-cone calculation equal to unity, we find a further reduction in the cross section of about a factor of two. The resulting light-cone cross section is similar in magnitude to the NRQCD factorization cross sections and shows only a modest enhancement over the light-cone cross section in which the relative momentum of the heavy-quark and antiquark is neglected.

Arkani-Hamed and Schmaltz have shown that proton stability need not originate from symmetries in a high energy theory. Instead the proton decay rate is suppressed if quarks and leptons are spatially separated in a compact extra dimension. This separation may be achieved by coupling five-dimensional fermions to a bulk scalar field with a nontrivial vacuum profile and requires relationships between the associated quark and lepton Yukawa couplings. We hypothesize that these relationships are the manifestation of an underlying symmetry. We further show that the Arkani-Hamed and Schmaltz proposal may suggest that proton stability is the result of an underlying symmetry, though not necessarily the traditional baryon number symmetry.

The three-year observations from the Wilkinson Microwave Anisotropy Probe have been hailed as giving the first clear indication of a spectral index $n_{\mathrm{s}}<1$. We point out that the data are equally well explained by retaining the assumption $n_{\mathrm{s}}=1$ and allowing the tensor-to-scalar ratio $r$ to be nonzero. The combination $n_{\mathrm{s}}=1$ and $r>0$ is given (within the slow-roll approximation) by a version of the intermediate inflation model with expansion rate $H(t)\propto t^{-1/3}$. We assess the status of this model in light of the WMAP3 data.

A dynamical description of the transitions between different backgrounds requires the existence of a background independent action which propagates the correct number of degrees of freedom and couples bulk supergravity to certain higher dimensional branes. We present classical equations for configurations that separate the world into regions with different flux parameters etc., and discuss the difficulties of trying to construct an action that describes the transitions between them within the framework of supergravity.

We match the Hagedorn/deconfinement temperature of planar $\mathcal{N}=4$ super Yang-Mills (SYM) on $\mathbb{R}\times S^3$ to the Hagedorn temperature of string theory on ${\mathrm{AdS}}_5\times S^5$. The match is done in a near-critical region where both gauge theory and string theory are weakly coupled. The near-critical region is near a point with zero temperature and critical chemical potential. On the gauge-theory side we are taking a decoupling limit found in Ref. [7] in which the physics of planar $\mathcal{N}=4$ SYM is given exactly by the ferromagnetic $XX{X}_{1/2}$ Heisenberg spin chain. We find moreover a general relation between the Hagedorn/deconfinement temperature and the thermodynamics of the Heisenberg spin chain and we use this to compute it in two distinct regimes. On the string-theory side, we identify the dual limit for which the string tension and string coupling go to zero. This limit is taken of string theory on a maximally supersymmetric pp-wave background with a flat direction, obtained from a Penrose limit of ${\mathrm{AdS}}_5\times S^5$. We compute the Hagedorn temperature of the string theory and find agreement with the Hagedorn/deconfinement temperature computed on the gauge-theory side.

We present explicit U-duality invariants for the $\mathbb{R}$, $\mathbb{C}$, $\mathbb{Q}$, $\mathbb{O}$ (real, complex, quaternionic, and octonionic) magic supergravities in four and five dimensions using complex forms with a reality condition. From these invariants we derive an explicit entropy function and corresponding stabilization equations which we use to exhibit stationary multicenter $1/2$ Bogomol’nyi-Prasad-Sommerfield (BPS) solutions of these $N=2$ $d=4$ theories, starting with the octonionic one with $E_{7(-25)}$ duality symmetry. We generalize to stationary $1/8$ BPS multicenter solutions of $N=8$, $d=4$ supergravity, using the consistent truncation to the quaternionic magic $N=2$ supergravity. We present a general solution of non-BPS attractor equations of the STU truncation of magic models. We finish with a discussion of the BPS-non-BPS relations and attractors in $N=2$ versus $N=5$, 6, 8.

In this paper we consider photon-photon scattering due to self-induced gravitational perturbations on a Minkowski background. We focus on four-wave interaction between plane waves with weakly space and time dependent amplitudes, since interaction involving a fewer number of waves is excluded by energy-momentum conservation. The Einstein-Maxwell system is solved perturbatively to third order in the field amplitudes and the coupling coefficients are found for arbitrary polarizations in the center of mass system. Comparisons with calculations based on quantum field theoretical methods are made, and the small discrepancies are explained.

We calculate, in a model, the beam spin asymmetry in semi-inclusive jet production in deep inelastic scattering. This twist-3, $T$-odd observable is nonzero due to final state strong interactions. With reasonable choices for the parameters, one finds an asymmetry of several percent, about the size seen experimentally. We present the result both as an explicit asymmetry calculation and as a model calculation of the new transverse-momentum dependent distribution function $g^{\perp }$.

Basing upon dual analytic models, we present arguments in favor of the parametrization of generalized parton distributions (GPD) in the form $\sim (x/g_0{)}^{(1-x)\tilde{\alpha }(t)}$, where $\tilde{\alpha }(t)=\alpha (t)-\alpha (0)$ is the nonlinear part of the Regge trajectory and $g_0$ is a parameter. For linear trajectories it reduces to earlier proposals. We compare the calculated moments of these GPD with the experimental data on form factors and find that the effects from the nonlinearity of Regge trajectories are large. By Fourier-transforming the obtained GPD, we access the spatial distribution of protons in the transverse plane. The relation between dual amplitudes with Mandelstam analyticity and composite models in the infinite-momentum frame is discussed, the integration variable in dual models being associated with the quark longitudinal momentum fraction $x$ in the nucleon.

We investigate the possibility of producing the enhancement observed in $J/\psi \to \gamma X$ with $X\to \omega \varphi$ at BES by intermediate meson rescatterings through $f_0(1710)\to PP\to \omega \varphi$, $f_0(1710)\to VV\to \omega \varphi$, and $f_0(1710)\to SS\to \omega \varphi$. We find that intermediate meson rescatterings can produce some enhancement near the $\omega \varphi$ threshold. Implications about the property of this enhancement are discussed.

The cross section of the diffractive Drell-Yan (DY) process, $pp\to \overline{l}lXp$, where the system $\overline{l}lX$ is separated by a large rapidity gap from the recoil proton, is calculated in the light-cone dipole approach. This process reveals unusual features, quite different from what is known for diffractive deeply inelastic scattering (DIS) and non-Abelian radiation: (i) the diffractive radiation of a heavy dilepton by a quark vanishes in the forward direction; (ii) the diffractive production of a dilepton is controlled by the large hadronic radius; (iii) in contrast with DIS where diffraction is predominantly soft, the diffractive DY reaction is semihard-semisoft; (iv) as a result of the saturated shape of the dipole cross section, the fraction of diffractive DY events steeply falls with energy but rises as a function of the hard scale. These features are common for other Abelian bremsstrahlung processes (higgsstrahlung, $Z$-strahlung, etc.). Measurements of diffractive DY processes at modern colliders would be a sensitive probe for the shape of the dipole cross section at large separations.

We develop the formalism for calculating semi-inclusive observables at high energy in the JIMWLK/KLWMIJ approach. This approach is valid for scattering of a small perturbative projectile on a large dense target. We consider several examples including diffractive processes, elastic and inclusive over the target degrees of freedom, scattering with fixed total transverse momentum transfer and inclusive gluon production. We discuss evolution of these observables with respect to various rapidity variables involved in their definitions (total rapidity, rapidity gap, width of diffractive interval, etc.). We also discuss the dipole model limit of these observables and derive closed simple (as opposed to functional) differential equations in this approximation. We point out that there are some interesting differences between the full JIMWLK/KLWMIJ evolution and the dipole model evolution of a diffractive cross section. In particular, we show that in the dipole approximation the target does not diffract beyond the valence rapidity interval, consistent with the intuition suggested by the Pomeron fan diagrams. On the other hand, such diffractive processes do exist in the full JIMWLK/KLWMIJ approach, albeit suppressed by the factor $1/N_c^2$.

We report a new measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using $425{\mathrm{pb}}^{-1}$ of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the $t\overline{t}$ content of the sample by tagging $b$ jets with a secondary vertex tagging algorithm, the $t\overline{t}$ production cross section is measured to be ${\sigma }_{p\overline{p}\to t\overline{t}+X}=6.6\pm 0.9(\mathrm{stat}+\mathrm{syst})\pm 0.4(\mathrm{lum})\mathrm{pb}$. This cross section is the most precise D0 measurement to date for $t\overline{t}$ production and is in good agreement with standard model expectations.