We study the coevolution of Yang-Mills fields and perfect fluids in Bianchi type I universes. We investigate numerically the evolution of the universe and the Yang-Mills fields during the radiation and dust eras of a universe that is almost isotropic. The Yang-Mills field undergoes small amplitude chaotic oscillations, as do the three expansion scale factors which are also displayed by the expansion scale factors of the universe. The results of the numerical simulations are interpreted analytically and compared with past studies of the cosmological evolution of magnetic fields in radiation and dust universes. We find that, whereas magnetic universes are strongly constrained by the microwave background anisotropy, Yang-Mills universes are principally constrained by primordial nucleosynthesis but the bound is comparatively weak with ${\Omega }_{\mathrm{YM}}<0.105{\Omega }_{\mathrm{rad}}$.

In certain string inspired higher dimensional cosmological models it has been conjectured that there is generic, chaotic oscillating behavior near the initial singularity—the Kasner parameters which characterize the asymptotic form of the metric jump between different, locally constant values and exhibit a never-ending oscillation as one approaches the singularity. In this paper we investigate a class of cosmological solutions with form fields and diagonal metrics which have a maximal number of composite electric $S$ branes. We look at two explicit examples in $D=4$ and $D=5$ dimensions that do not have chaotic oscillating behavior near the singularity. When the composite branes are replaced by noncomposite branes chaotic oscillating behavior again occurs.

The evolution of a scalar field is explored taking into account the presence of a background fluid in a positively curved universe in the framework of loop quantum cosmology. Though the mechanism that provides the initial conditions for inflation extensively studied in the literature is still available in this setup, it demands that the initial kinetic energy of the field be comparable to the energy density of the background fluid if the field is initially situated at the minimum of the potential. It is found, however, that for potentials with a minimum such as the chaotic inflation model, there is an additional mechanism that can provide the correct initial conditions for successful inflation even if initially the kinetic energy of the field is subdominant by many orders of magnitude. In this latter mechanism the field switches direction when the Universe is still in the expanding phase. The kinetic energy gained while the field rolls down the potential is subsequently enhanced when the Universe enters the collapsing phase pushing the field one step up the potential. This behavior is repeated on every cycle of contraction and expansion of the Universe until the field becomes dominant and inflation follows.

We investigate the possibility of generating initial conditions for cosmological N-body simulations by simulating a system whose correlations at thermal equilibrium approximate well those of cosmological density perturbations. The system is an appropriately modified version of the standard “one component plasma” (OCP). We show first how a well-known semianalytic method can be used to determine the potential required to produce the desired correlations, and then verify our results for some cosmological type spectra with simulations of the full molecular dynamics. The advantage of the method, compared to the standard one, is that it gives by construction an accurate representation of both the real and reciprocal space correlation properties of the theoretical model. Furthermore the distributions are also statistically homogeneous and isotropic. We discuss briefly the modifications needed to implement the method to produce configurations appropriate for large N-body simulations in cosmology, and also the generation of initial velocities in this context.

We point out that the QCD corrections to the gluon-fusion Higgs boson production cross section at the LHC are very similar to the corrections to the Higgs decay rate into two gluons. Consequently, the ratio of these two quantities has a theoretical uncertainty smaller than the uncertainty in the cross section alone by a factor of 2. We note that since this ratio is the theoretical input to analyses of Higgs coupling extractions at the LHC, the reduced uncertainty should be used; in previous studies, the full cross section uncertainty was employed.

When relating the strong coupling ${\alpha }_s$, measured at the scale of the $Z$ boson mass, to its numerical value at some higher energy, for example, the scale of grand unification, it is important to include higher order corrections both in the running of ${\alpha }_s$ and the decoupling of the heavy particles. We compute the two-loop matching coefficients for ${\alpha }_s$ within the minimal supersymmetric standard model which are necessary for a consistent three-loop evolution of the strong coupling constant. Different scenarios for the hierarchy of the supersymmetric scales are considered and the numerical effects are discussed. We find that the three-loop effects can be as large as and sometimes even larger than the uncertainty induced by the current experimental accuracy of ${\alpha }_s(M_Z)$.

The compatibility of producing the observed amount of dark matter, as indicated by the Wilkinson Microwave Anisotropy Probe (WMAP) data, through the relic abundance of neutralinos with Yukawa unification and with the measured rate of $b\to s\gamma$ is analyzed in mSUGRA and extended SUGRA unified models with the inclusion of $CP$ phases. The $CP$ phases affect the analysis in several ways, e.g., through the threshold corrections to the $b$-quark mass, via their effects on the neutralino relic density and through the supersymmetry (SUSY) contribution to the $\mathrm{BR}(b\to s\gamma )$ which is sensitive to the $CP$ phases. We present some specific models with large SUSY phases, which can accommodate the fermion electric dipole moment constraints and give a neutralino relic density in agreement with observations as well as with the $b\mathrm{\text{−}}\tau$ unification constraint. The possibility of achieving WMAP relic density constraints with full Yukawa unification is also explored.

We investigate the sensitivity of future photon-photon colliders to low scale gravity scenarios via the process $\gamma \gamma \to ZZ$ where the Kaluza-Klein boson exchange contributes only when the initial state photons have opposite helicity. We contrast this with the situation for the process $\gamma \gamma \to \gamma \gamma$ where the $t$ and $u$ channels also contribute. We include the one-loop standard model background whose interference with the graviton exchange determines the experimental reach in measuring any deviation from the standard model expectations and explore how polarization can be exploited to enhance the signal over background. We find that a 1 TeV linear collider has an experimental reach to mass scale of about 4 TeV in this channel.

We perform a phenomenological analysis of the decays $\overline{B}\to D^{**}\pi$, where $D^{**}$ is a $P$-wave excited meson with total angular momentum $j=\frac{1}{2}$ or $\frac{3}{2}$ for the light cloud, recently measured by the Belle Collaboration in the modes ${\overline{B}}^0\to D^{**+}{\pi }^{-}$ (Class I) and $B^{-}\to D^{**0}{\pi }^{-}$ (Class III). Making the reasonable assumption of naive factorization, that we test in $B\to D(D^{*})\pi$ decays, Class I decays allow to extract the Isgur-Wise form factors ${\tau }_{1/2}(w)$, ${\tau }_{3/2}(w)$ at $w\cong w_{\max }$ ($q^2\cong 0$). We obtain ${\tau }_{1/2}(w_{\max })<0.20$, ${\tau }_{3/2}(w_{\max })=0.31\pm 0.12$. We discuss the question of the $w$ dependence of these IW functions. We find agreement with the Bakamjian-Thomas quark model of form factors and, extrapolating at $w=1$, with Bjorken and Uraltsev sum rules. We discuss also Class III decays, where the $D^{**0}$ $(j=\frac{1}{2})$ emission diagram contributes. We extract the corresponding $f_{D_{1/2}}$ decay constant, that is in agreement with theoretical estimates at finite mass. Finally, we must warn that $1/m_Q$ corrections could be large and upset the results of the present stage of this analysis. On the other hand, we confront present data on the semileptonic rate of $B$ mesons to excited states with theoretical expectations.

We calculate the inclusive single-gluon production cross section in high energy onium-onium scattering including pomeron loop effects. The resulting inclusive cross section is given by the $k_T$-factorization formula with one of the unintegrated gluon distribution functions depending on the total onium-onium scattering cross section, which includes all pomeron loops and has to be found independently. We discuss the limits of applicability of our result and argue that they are given by the limits of applicability of the pomeron loop resummation approach. Since the obtained $k_T$-factorization formula is infrared divergent we conclude that, in order to consistently calculate the (infrared-finite) gluon production cross section in onium-onium scattering, one has to include corrections going beyond the pomeron loop approximation.

The standard model explanations of the anomalously-large transverse polarization fraction $f_T$ in $B\to \varphi K^{*}$ can be tested by measuring the polarizations of the two decays $B^{+}\to {\rho }^{+}{K}^{*0}$ and $B^{+}\to {\rho }^0{K}^{*+}$. For the scenario in which the transverse polarizations of both $B\to \rho K^{*}$ decays are predicted to be large, we derive a simple relation between the $f_T$’s of these decays. If this relation is not confirmed experimentally, this would yield an unambiguous signal for new physics. The new-physics operators which can account for the discrepancy in $B\to \pi K$ decays will also contribute to the polarization states of $B\to \rho K^{*}$. We compute these contributions and show that there are only two operators which can simultaneously account for the present $B\to \pi K$ and $B\to \rho K^{*}$ data. If the new physics obeys an approximate U-spin symmetry, the $B\to \varphi K^{*}$ measurements can also be explained.

A simple and well-motivated explanation for the origin of dark matter is that it consists of thermal relic particles that get their mass entirely through electroweak symmetry breaking. Furthermore, this possibility suggests an environmental explanation of the hierarchy between the weak and Planck scales and of the small value of the cosmological constant relative to the weak scale. In simple models with these features, the dark matter is a mixture of two Dirac neutrinos with opposite isospin, and so has suppressed coupling to the $Z$. Other minimal models of this form are also consistent with gauge coupling unification. We predict a dark matter (DM) mass of $m_{\mathrm{DM}}\approx 45\mathrm{GeV}$ or $m_{\mathrm{DM}}\approx 90–95\mathrm{GeV}$ and DM-neutron spin-independent cross sections ${\sigma }_{\mathrm{DM}\mathrm{\text{−}}n}\sim {10}^{-6}–{10}^{-8}\mathrm{pb}$. An enhancement of the galactic halo gamma ray and positron flux coming from annihilations of these particles is also expected across the $\sim 1–100\mathrm{GeV}$ range.

We study phenomenological predictions in the scenario with the quasidegenerate relation among neutrino Dirac masses, $m_{D1}\simeq m_{D2}<m_{D3}$, assuming the bimaximal mixing at the grand unification scale in supersymmetric standard models with right-handed neutrinos. A sufficient lepton number asymmetry can be produced for successful leptogenesis. The lepton flavor violating process $\mu \to e\gamma$ can be enhanced due to the Majorana phase, so that it can be detectable at forthcoming experiments. The processes $\tau \to e\gamma$ and $\tau \to \mu \gamma$ are suppressed because of the structure of neutrino Dirac masses, and their branching ratios are smaller than that of $\mu \to e\gamma$.

We calculate the Cherenkov radiation from an $e^{+}{e}^{-}$ pair at small separations, as occurs shortly after a pair conversion. The radiation is reduced (compared to that from two independent particles) when the pair separation is smaller than the wavelength of the emitted light. We estimate the reduction in light in large electromagnetic showers, and discuss the implications for detectors that observe Cherenkov radiation from showers in the Earth’s atmosphere, as well as in oceans and Antarctic ice.

A sample of kinematically identified $K^{+}\to {\pi }^{+}{\pi }^0$ decays obtained with the E949 detector was used to search for the helicity-suppressed decay ${\pi }^0\to \nu \overline{\nu }$ resulting in an upper limit of $2.7\times {10}^{-7}$ at $90\%$ confidence level. The upper limit is also applicable to ${\pi }^0$ decays into unknown weakly-interacting particles.

We introduce a class of models in which statistical isotropy is broken spontaneously in the CMB by a nonlinear response to long-wavelength fluctuations in a mediating field. These fluctuations appear as a gradient locally and pick out a single preferred direction. The nonlinear response imprints this direction in a range of multipole moments. We consider two manifestations of isotropy breaking: additive contributions and multiplicative modulation of the intrinsic anisotropy. Since the Wilkinson microwave anisotropy probe (WMAP) exhibits an alignment of power deficits, an additive contribution is less likely to produce the observed alignments than the usual isotropic fluctuations, a fact which we illustrate with an explicit cosmological model of long-wavelength quintessence fluctuations. This problem applies to other models involving foregrounds or background anisotropy that seek to restore power to the CMB. Additive models that account directly for the observed power exacerbate the low power of the intrinsic fluctuations. Multiplicative models can overcome these difficulties. We construct a proof of principle model that significantly improves the likelihood and generates stronger alignments than WMAP in 30%–45% of realizations.

The overlap of the nucleons in nuclei plays an important role in understanding the nuclear dependence of deep inelastic scattering data. It is shown that the nuclear modification of the higher twist scale can be essentially determined by the overlapping volume per nucleon and this effect gives a large contribution to nuclear shadowing for small $x$ and low $Q^2$. In this kinematical region there is also a moderate enhancement of the longitudinal structure function in nuclei.

We study resonant $CP$ violation in the Higgsstrahlung process $e^{+}{e}^{-}\to H_{1,2,3}(Z\to e^{+}{e}^{-},{\mu }^{+}{\mu }^{-})$ and subsequent decays $H_{1,2,3}\to b\overline{b},{\tau }^{-}{\tau }^{+}$, in the minimal supersymmetric extension of the standard model (MSSM) with Higgs-sector $CP$ violation induced by radiative corrections. At a high-energy $e^{+}{e}^{-}$ linear collider, the recoil-mass method enables one to determine the invariant mass of a fermion pair produced by Higgs decays with a precision as good as 1 GeV. Assuming an integrated luminosity of $100{\mathrm{fb}}^{-1}$, we show that the production line shape of a coupled system of neutral Higgs bosons decaying into $b\overline{b}$ quarks is sensitive to the $CP$-violating parameters. When the Higgs bosons decay into ${\tau }^{-}{\tau }^{+}$, two $CP$ asymmetries can be defined using the longitudinal and transverse polarizations of the $\tau$ leptons. Taking into account the constraints from electric dipole moments, we find that these $CP$ asymmetries can be as large as 80%, in a trimixing scenario where all three neutral Higgs states of the MSSM are nearly degenerate and mix significantly.

The most recent data on the weighted transverse single spin asymmetry $A_{UT}^{\sin ({\varphi }_h-{\varphi }_S)}$ from HERMES and COMPASS Collaborations are analyzed within the LO parton model with unintegrated parton distribution and fragmentation functions; all transverse motions are taken into account, with exact kinematics, in the elementary interactions. The overall quality of the data is such that, for the first time, a rather well constrained extraction of the Sivers function for $u$ and $d$ quarks is possible and is performed. Comparisons with models are made. Based on the extracted Sivers functions, predictions for $A_{UT}^{\sin ({\varphi }_h-{\varphi }_S)}$ asymmetries at JLab are given; suggestions for further measurements at COMPASS, with a transversely polarized hydrogen target and selecting favorable kinematical ranges, are discussed. Predictions are also presented for single spin asymmetries in Drell-Yan processes at the Relativistic Heavy Ion Collider and the Facility for Antiproton and Ion Research at GSI-Darmstadt.