We investigate the relic density $n_{\chi }$ of nonrelativistic long-lived or stable particles $\chi$ in cosmological scenarios in which the temperature $T$ is too low for $\chi$ to achieve full chemical equilibrium. The case with a heavier particle decaying into $\chi$ is also investigated. We derive approximate solutions for $n_{\chi }(T)$ which accurately reproduce numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the $\chi$ number density. However, it does give the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures.

We present a Monte Carlo simulation for the response of the Laser Interferometer Space Antenna (LISA) to the galactic gravitational wave background. The simulated data streams are used to estimate the number and type of binary systems that will be individually resolved in a 1-year power spectrum. We find that the background is highly non-Gaussian due to the presence of individual bright sources but, once these sources are identified and removed, the remaining signal is Gaussian. We also present a new estimate of the confusion noise caused by unresolved sources that improves on earlier estimates.

We investigate the behavior of the QCD evolution towards high energy, in the diffusive approximation, in the limit where the fluctuation contribution is large. Our solution for the equivalent stochastic Fisher equation predicts the amplitude as well as the whole set of correlators in the strong-noise limit. The speed of the front and the diffusion coefficient are obtained. We analyze the consequences on high-energy evolution in QCD.

We study $\mathcal{O}({\alpha }_s^2{\beta }_0)$ perturbative corrections to matrix elements entering two-body exclusive decays of the form $\overline{B}\to \pi \pi$, $\pi K$ in the QCD factorization formalism, including chirally enhanced power corrections, and discuss the effect of these corrections on direct $CP$ asymmetries, which receive their first contribution at $\mathcal{O}({\alpha }_s)$. We find that the $\mathcal{O}({\alpha }_s^2{\beta }_0)$ corrections are often as large as the $\mathcal{O}({\alpha }_s)$ corrections. We find large uncertainties due to renormalization scale dependence as well as poor knowledge of the nonperturbative parameters. We assess the effect of the perturbative corrections on the direct $CP$ violation parameters of $B^0\to {\pi }^{+}{\pi }^{-}$.

We consider modifications of the standard nonlinear QCD evolution in an attempt to account for some of the missing ingredients discussed recently, such as correlations, discreteness in gluon emission and Pomeron loops. The evolution is numerically performed using the Balitsky-Kovchegov equation on individual configurations defined by a given initial value of the saturation scale, for reduced rapidities $y=({\alpha }_s{N}_c/\pi )Y<10$. We consider the effects of averaging over configurations as a way to implement correlations, using three types of Gaussian averaging around a mean saturation scale. Further, we heuristically mimic discreteness in gluon emission by considering a modified evolution in which the tails of the gluon distributions are cut off. The approach to scaling and the behavior of the saturation scale with rapidity in these modified evolutions are studied and compared with the standard mean-field results. For the large but finite values of rapidity explored, no strong quantitative difference in scaling for transverse momenta around the saturation scale is observed. At larger transverse momenta, the influence of the modifications in the evolution seems most noticeable in the first steps of the evolution. No influence on the rapidity behavior of the saturation scale due to the averaging procedure is found. In the cutoff evolution the rapidity evolution of the saturation scale is slowed down and strongly depends on the value of the cutoff. Our results stress the need to go beyond simple modifications of evolution by developing proper theoretical tools that implement such recently discussed ingredients.

We present Monte Carlo simulations of both the Sivers and the Boer-Mulders effects in the polarized Drell-Yan ${\pi }^{\pm }{p}^{\uparrow }\to {\mu }^{+}{\mu }^{-}X$ process at a kinematics suitable to the COMPASS setup. For the Sivers effect, we adopt two different parametrizations for the Sivers function to explore the statistical accuracy required to extract unambiguous information on this parton density. In particular, we verify the possibility of checking its predicted sign change between semi-inclusive deep-inelastic scattering (SIDIS) and Drell-Yan processes, a crucial test of nonperturbative QCD. For the Boer-Mulders effect, because of the lack of parametrizations we can make only guesses. The goal is to explore the possibility of extracting information on the transversity distribution, the missing piece necessary to complete the knowledge of the nucleon spin structure at leading twist, and the Boer-Mulders function, which is related to the long-standing problem of the violation of the Lam-Tung sum rule in the unpolarized Drell-Yan cross section.

The chiral quark model gives a reasonably good description of many low-energy observables by incorporating the effective degrees carried by the constituent quarks and Goldstone bosons. We calculate the decuplet to octet transition magnetic moments and the decay widths of several excited hyperons using this model. The various radiative decay widths from the chiral quark roughly agree with experimental data including recent JLAB measurement.

We present the results of a search for the production of an excited state of the muon, ${\mu }^{*}$, in proton antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately $380{\mathrm{pb}}^{-1}$. We search for ${\mu }^{*}$ in the process $p\overline{p}\to {\mu }^{*}\mu$, with the ${\mu }^{*}$ subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes ${\mu }^{*}$ production by four-fermion contact interactions and ${\mu }^{*}$ decay via electroweak processes, we set a 95% confidence level production cross section upper limit ranging from 0.057 to 0.112 pb, depending on the mass of the excited muon. Choosing the scale for contact interactions to be $\Lambda =1\mathrm{TeV}$, excited muon masses below 618 GeV are excluded.

We present updated results on time-dependent $CP$ asymmetries in fully reconstructed $B^0\to D^{(*)\pm }{\pi }^{\mp }$ and $B^0\to D^{\pm }{\rho }^{\mp }$ decays in approximately $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ events collected with the BABAR detector at the PEP-II asymmetric-energy $B$ factory at SLAC. From a time-dependent maximum-likelihood fit we obtain for the parameters related to the $CP$ violation angle $2\beta +\gamma$: $a^{D\pi }=-0.010\pm 0.023\pm 0.007$, $c_{\mathrm{lep}}^{D\pi }=-0.033\pm 0.042\pm 0.012$, $a^{D^{*}\pi }=-0.040\pm 0.023\pm 0.010$, $c_{\mathrm{lep}}^{D^{*}\pi }=0.049\pm 0.042\pm 0.015$,$a^{D\rho }=-0.024\pm 0.031\pm 0.009$, $c_{\mathrm{lep}}^{D\rho }=-0.098\pm 0.055\pm 0.018$, where the first error is statistical and the second is systematic. Using other measurements and theoretical assumptions, we interpret the results in terms of the angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle and find $|\sin (2\beta +\gamma )|>0.64(0.40)$ at 68% (90%) confidence level.

Cosmological parameter estimation exercises usually make the approximation that the three standard neutrinos have degenerate mass, which is at odds with recent terrestrial measurements of the difference in the square of neutrino masses. In this paper we examine whether the use of this approximation is justified for the cosmic microwave background (CMB) spectrum, matter power spectrum, and the CMB lensing potential power spectrum. We find that, assuming $\delta m_{23}^2\sim 2.5\times {10}^{-3}{\mathrm{eV}}^2$ in agreement with recent Earth-based measurements of atmospheric neutrino oscillations, the correction due to nondegeneracy is of the order of precision of present numerical codes and undetectable for the foreseeable future for the CMB and matter power spectra. An ambitious experiment that could reconstruct the lensing potential power spectrum to the cosmic variance limit up to $\ell \sim 1000$ will have to take the effect into account in order to avoid biases. The degeneracies with other parameters, however, will make the detection of the neutrino mass difference impossible. We also show that relaxing the bound on the neutrino mass difference will also increase the error bar on the sum of neutrino masses by a factor of up to a few. For exotic models with significantly nondegenerate neutrinos the corrections due to nondegeneracy could become important for all the cosmological probes discussed here.

The details of Super-Kamiokande-I’s solar neutrino analysis are given. Solar neutrino measurement in Super-Kamiokande is a high statistics collection of ${}^8\mathrm{B}$ solar neutrinos via neutrino-electron scattering. The analysis method and results of the 1496 day data sample are presented. The final oscillation results for the data are presented also.

We show that in hybrid inflation it is possible to generate large second-order perturbations in the cosmic microwave background due to the instability of the tachyonic field during preheating. We carefully calculate this effect from the tachyon contribution to the gauge-invariant curvature perturbation, clarifying some confusion in the literature concerning nonlocal terms in the tachyon curvature perturbation; we show explicitly that such terms are absent. We quantitatively compute the non-Gaussianity generated by the tachyon field during the preheating phase and translate the experimental constraints on the nonlinearity parameter $f_{NL}$ into constraints on the parameters of the model. We also show that nonscale-invariant second-order perturbations from the tachyon field with spectral index $n=4$ can become larger than the inflaton-generated first-order perturbations, leading to stronger constraints than those coming from non-Gaussianity. The width of the excluded region in terms of the logarithm of the dimensionless coupling $g$, grows linearly with the log of the ratio of the Planck mass to the tachyon VEV, $\log (M_p/v)$; hence very large regions are ruled out if the inflationary scale $v$ is small. We apply these results to string-theoretic brane-antibrane inflation, and find a stringent upper bound on the string coupling, $g_s<{10}^{-4.5}$.

Motivated by grand unification, we study the properties of domain walls formed in a model with $SU(5)\times Z_2$ symmetry which is spontaneously broken to $SU(3)\times SU(2)\times U(1)/Z_6$, and subsequently to $SU(3)\times U(1)/Z_3$. Even after the first stage of symmetry breaking, the $SU(3)$ symmetry is broken to $SU(2)\times U(1)/Z_2$ on the domain wall. In a certain range of parameters, flux tubes carrying color- and hyper-charge live on the domain wall and appear as “boojums” when viewed from one side of the domain wall. Magnetic monopoles are also formed in the symmetry breaking and those carrying color and hyper-charge can be repelled from the wall due to the Meissner effect, or else their magnetic flux can penetrate the domain wall in quantized units. After the second stage of symmetry breaking, fermions can transmute when they scatter with the domain wall, providing a simpler version of fermion-monopole scattering: for example, neutrinos can scatter into d-quarks, leaving behind electric charge and color which is carried by gauge field excitations living on the domain wall.

In this paper, we extend the analysis of the Lorentz-violating Quantum Electrodynamics to the non-Abelian case: an SO(3) Yang-Mills Lagrangian with the addition of the non-Abelian Chern-Simons-type term. We consider the spontaneous symmetry breaking of the model and inspect its spectrum in order to check if unitarity and causality are respected. An analysis of the topological structure is also carried out and we show that a ’t Hooft-Polyakov solution for monopoles is still present.

It is commonly asserted that the electromagnetic current is conserved and therefore is not renormalized. Within QED we show (a) that this statement is false, (b) how to obtain the renormalization of the current to all orders of perturbation theory, and (c) how to correctly define an electron number operator. The current mixes with the four-divergence of the electromagnetic field-strength tensor. The true electron number operator is the integral of the time component of the electron number density, but only when the current differs from the $\overline{\mathrm{MS}}$-renormalized current by a definite finite renormalization. This happens in such a way that Gauss’s law holds: the charge operator is the surface integral of the electric field at infinity. The theorem extends naturally to any gauge theory.

Radion stabilization is analyzed in 5-dimensional models with branes in the presence of Gauss-Bonnet interactions. The Goldberger-Wise mechanism is considered for static and inflating backgrounds. The necessary and sufficient conditions for stability are given for the static case. The influence of the Gauss-Bonnet term on the radion mass and the interbrane distance is analyzed and illustrated by numerical examples. The interplay between the radion stabilization and the cosmological constant problem is discussed.

Two Fokker actions and corresponding equations of motion are obtained for two point particles in a post-Minkowski framework, in which the field of each particle is given by the half-retarded $+$ half-advanced solution to the linearized Einstein equations. The first action is parametrization invariant, the second a generalization of the affinely parametrized quadratic action for a relativistic particle. Expressions for a conserved 4-momentum and angular momentum tensor are obtained in terms of the particles’ trajectories in this post-Minkowski approximation. A formal solution to the equations of motion is found for a binary system with circular orbits. For a bound system of this kind, the post-Minkowski solution is a toy model that omits nonlinear terms of relevant post-Newtonian order; and we also obtain a Fokker action that is accurate to first post-Newtonian order, by adding to the post-Minkowski action a term cubic in the particle masses. Curiously, the conserved energy and angular momentum associated with the Fokker action are each finite and well-defined for this bound 2-particle system despite the fact that the total energy and angular momentum of the radiation field diverge. Corresponding solutions and conserved quantities are found for two scalar charges (for electromagnetic charges we exhibit the solution found by Schild). For a broad class of parametrization-invariant Fokker actions and for the affinely parametrized action, binary systems with circular orbits satisfy the relation $dE=\Omega dL$ (a form of the first law of thermodynamics), relating the energy, angular velocity and angular momentum of nearby equilibrium configurations.

A new six-parametric, axisymmetric, and asymptotically flat exact solution of Einstein-Maxwell field equations having reflection symmetry is presented. It has arbitrary physical parameters of mass, angular momentum, mass-quadrupole moment, current octupole moment, electric charge, and magnetic dipole, so it can represent the exterior field of a rotating, deformed, magnetized, and charged object; some properties of the closed-form analytic solution such as its multipolar structure, electromagnetic fields, and singularities are also presented. In the vacuum case, this analytic solution is matched to some numerical interior solutions representing neutron stars, calculated by Berti and Stergioulas [E. Berti and N. Stergioulas, Mon. Not. R. Astron. Soc. 350, 1416 (2004)], imposing that the multipole moments be the same. As an independent test of accuracy of the solution to describe exterior fields of neutron stars, we present an extensive comparison of the radii of innermost stable circular orbits (ISCOs) obtained from the Berti and Stergioulas numerical solutions, the Kerr solution [R. P. Kerr, Phys. Rev. Lett. 11, 237 (1963)], the Hartle and Thorne solution [J. B. Hartle and K. S. Thorne, Astrophys. J. 153, 807 (1968)], an analytic series expansion derived by Shibata and Sasaki [M. Shibata and M. Sasaki, Phys. Rev. D 58, 104011 (1998)], and our exact solution. We found that radii of ISCOs from our solution fits better than others with realistic numerical interior solutions.

In models with TeV-scale gravity it is expected that mini black holes will be produced in near-future accelerators. On the other hand, TeV-scale gravity is plagued with many problems like fast proton decay, unacceptably large $n-\overline{n}$ oscillations, flavor changing neutral currents, large mixing between leptons, etc. Most of these problems can be solved if different fermions are localized at different points in the extra dimensions. We study the cross section for the production of black holes and their angular momentum distribution in these models with “split” fermions. We find that, for a fixed value of the fundamental mass scale, the total production cross section is reduced compared with models where all the fermions are localized at the same point in the extra dimensions. Fermion splitting also implies that the bulk component of the black hole angular momentum must be taken into account in studies of the black hole decay via Hawking radiation.