Neutrinos from far-away sources annihilating at the Z-resonance on relic neutrinos may give origin to the extreme-energy cosmic rays (EECR). If “Z-bursts” are responsible for the EECR events, then we show that the nonobservation of cosmic ray events at energies above $2\times {10}^{20}\mathrm{e}\mathrm{V}$ by the AGASA Collaboration implies a lower bound $\sim 0.3\mathrm{e}\mathrm{V}$ on the relic neutrino mass. Since this mass exceeds the mass-squared differences inferred from oscillation physics, the bound in fact applies to all three neutrino masses. Together with the upper bound provided by comparisons of the CMB anisotropy with large-scale structure, this bound leaves only a small interval for neutrino masses around 0.3 eV, if Z-bursts are to explain the existing EECR events.

In the context of three-flavor neutrino mixing, we present a thorough study of the phenomenological constraints applicable to three observables sensitive to absolute neutrino masses: The effective neutrino mass in Tritium beta-decay $(m_{\beta })$; the effective Majorana neutrino mass in neutrinoless double beta-decay $(m_{\beta \beta })$; and the sum of neutrino masses in cosmology $(\Sigma )$. We discuss the correlations among these variables which arise from the combination of all the available neutrino oscillation data, in both normal and inverse neutrino mass hierarchy. We set upper limits on $m_{\beta }$ by combining updated results from the Mainz and Troitsk experiments. We also consider the latest results on $m_{\beta \beta }$ from the Heidelberg-Moscow experiment, both with and without the lower bound claimed by such experiment. We derive upper limits on $\Sigma$ from an updated combination of data from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite and the two degrees Fields (2dF) Galaxy Redshifts Survey, with and without Lyman-$\alpha$ forest data from the Sloan Digital Sky Survey (SDSS), in models with a nonzero running of the spectral index of primordial inflationary perturbations. The results are discussed in terms of two-dimensional projections of the globally allowed region in the $(m_{\beta },m_{\beta \beta },\Sigma )$ parameter space, which neatly show the relative impact of each data set. In particular, the (in)compatibility between $\Sigma$ and $m_{\beta \beta }$ constraints is highlighted for various combinations of data. We also briefly discuss how future neutrino data (both oscillatory and nonoscillatory) can further probe the currently allowed regions.

The cosmology in the Hubble expansion era of the Horava-Witten M theory compactified on a Calabi-Yau threefold is studied in the reduction to five-dimensions where the effects of the Calabi-Yau manifold are summarized by the volume modulus, and all perturbative potentials are included. Matter on the branes are treated as first order perturbations of the static vacuum solution, and all equations in the bulk and all boundary conditions on both end branes are imposed. It is found that for a static volume modulus and a static fifth dimension, $y$, one can recover the four-dimensional Robertson Friedmann Walker cosmology for relativistic matter on the branes, but not for nonrelativistic matter. In this case, the Hubble parameter $H$ becomes independent of $y$ to first order in matter density. This result holds also when an arbitrary number of 5-branes are included in the bulk. The five-dimensional Horava-Witten model is compared with the Randall-Sundrum phenomenology with a scalar field in the bulk where a bulk and brane potential are used so that the vacuum solutions can be rigorously obtained. (In the Appendix, the difficulty of obtaining approximate vacuum solutions for other potentials is discussed.) In this case nonrelativistic matter is accommodated by allowing the distance between the branes to vary. It is suggested that nonperturbative potentials for the vacuum solution of Horava-Witten theory are needed to remove the inconsistency that nonrelativistic matter creates.

The $1/N$ expansion of the two-particle irreducible (2PI) effective action is employed to compute universal properties at the 2nd order phase transition of an $O(N)$-symmetric $N$-vector model directly in three-dimensions. At next-to-leading-order the approach cures the spurious small-$N$ divergence of the standard (1PI) $1/N$ expansion for a computation of the critical anomalous dimension $\eta (N)$, and leads to improved estimates already for moderate values of $N$.

An impressive amount of different astrophysical data converges towards the picture of a spatially flat Universe undergoing today a phase of accelerated expansion. The nature of the dark energy dominating the energy content of the Universe is still unknown, and a lot of different scenarios are viable candidates to explain cosmic acceleration. Most of the methods employed to test these cosmological models are essentially based on distance measurements to a particular class of objects. A different method, based on the lookback time to galaxy clusters and the age of the Universe, is used here. In particular, we constrain the characterizing parameters of three classes of dark energy cosmological models to see whether they are in agreement with this kind of data, based on time measurements rather than distance observations.

Most active galactic nuclei (AGN) lack prominent jets, and show modest radio emission and significant x-ray emission which arises mainly from the galactic core, very near the central black hole. We use a quantitative scenario of such core-dominated radio-quiet AGN, which attributes a substantial fraction of the x-ray emission to the presence of abortive jets involving the collision of gas blobs in the core. Here we investigate the consequences of the acceleration of protons in the shocks from such collisions. We find that protons will be accelerated up to energies above the pion photoproduction threshold on both the x rays and the UV photons from the accretion disk. The secondary charged pions decay, producing neutrinos. We predict significant fluxes of TeV-PeV neutrinos, and show that the AMANDA II detector is already constraining several important astrophysical parameters of these sources. Larger cubic kilometer detectors such as IceCube will be able to detect such neutrinos in less than one year of operation, or otherwise rule out this scenario.

In this note we show that vector perturbations exhibit growing mode solutions in a contracting Universe, such as the contracting phase of the pre big bang or the cyclic/ekpyrotic models of the Universe. This is not a gauge artifact and will in general lead to the breakdown of perturbation theory—a severe problem that has to be addressed in any bouncing model. We also comment on the possibility of explaining, by means of primordial vector perturbations, the existence of the observed large-scale magnetic fields. This is possible since they can be seeded by vorticity.

We present a revised interpretation of recent analysis of supernovae data. We evaluate the effect of the priors on the extraction of the dark energy equation of state. We find that the conclusions depend strongly on the ${\Omega }_M$ prior value and on its uncertainty and show that a biased fitting procedure applied on non concordant simulated data can converge to the “concordance model.” Relaxing the prior on ${\Omega }_M$ points to other sets of solutions, which are not excluded by observational data.

Starting from very high-energy inelastic electron-nucleon scattering with a production of a hadronic state $X$ to be moved closely to the direction of the initial nucleon, then utilizing analytic properties of parts of forward virtual Compton scattering amplitudes on proton and neutron, one obtains the relation between nucleon form factors and a difference of proton and neutron differential electroproduction cross sections. In particular, for the case of small transferred momenta, one finally derives sum rule, relating Dirac proton mean square radius and anomalous magnetic moments of proton and neutron to the integral over a difference of the total proton and neutron photoproduction cross sections.

We extend the earlier suggested QCD-motivated model for the $Q^2$ dependence of the generalized Gerasimov-Drell-Hearn (GDH) sum rule which assumes the smooth dependence of the structure function $g_T$, while the sharp dependence is due to the $g_2$ contribution and is described by the elastic part of the Burkhardt-Cottingham sum rule. The model successfully predicts the low crossing point for the proton GDH integral, but is at variance with the recent very accurate JLAB data. We show that, at this level of accuracy, one should include the previously neglected radiative and power QCD corrections, as boundary values for the model. We stress that the GDH integral, when measured with such a high accuracy achieved by the recent JLAB data, is very sensitive to QCD power corrections. We estimate the value of these power corrections from the JLAB data at $Q^2\sim 1{\mathrm{G}\mathrm{e}\mathrm{V}}^2$. The inclusion of all QCD corrections leads to a good description of proton, neutron, and deuteron data at all $Q^2$.

The shadowing and antishadowing of nuclear structure functions in the Gribov-Glauber picture is due, respectively, to the destructive and constructive interference of amplitudes arising from the multiple scattering of quarks in the nucleus. The effective quark-nucleon scattering amplitude includes Pomeron and Odderon contributions from multigluon exchange as well as Reggeon quark-exchange contributions. We show that the coherence of these multiscattering nuclear processes leads to shadowing and antishadowing of the electromagnetic nuclear structure functions in agreement with measurements. This picture leads to substantially different antishadowing for charged and neutral current reactions, thus affecting the extraction of the weak-mixing angle ${\theta }_W$. We find that part of the anomalous NuTeV result for ${\theta }_W$ could be due to the nonuniversality of nuclear antishadowing for charged and neutral currents. Detailed measurements of the nuclear dependence of individual quark structure functions are thus needed to establish the distinctive phenomenology of shadowing and antishadowing and to make the NuTeV results definitive.

We study the $B\to \varphi K_S$ decay in a supersymmetric (SUSY) SO(10) grand unified theory (GUT). We calculate the mass spectrum of sparticles for a given set of parameters at the grand unified theory (GUT) scale. We complete the calculations of the Wilson coefficients of operators including the new operators which are induced by neutral Higgs boson (NHB) penguins at LO using the mass insertion approximation (MIA) with double insertions. It is shown that the recent experimental results on the time-dependent CP asymmetry $S_{\varphi K}$ in $B\to \varphi K_S$, which is negative and cannot be explained in the standard model (SM), can be explained in the model where there are flavor nondiagonal right-handed down squark mass matrix elements of second and third generations whose size satisfies all relevant constraints from known experiments ($\tau \to \mu \gamma$, $B\to X_S\gamma$, $B_s\to {\mu }^{+}{\mu }^{-}$, $B\to X_s{\mu }^{+}{\mu }^{-}$, $B\to X_{s}g$, $\Delta M_s$, etc.). At the same time, the branching ratio for the decay can also be in agreement with experimental measurements.

A predictive framework for supersymmetry at the TeV scale is presented, which incorporates the Ciafaloni-Pomarol mechanism for the dynamical determination of the $\mu$ parameter. The $\mu$ parameter of the minimal supersymmetric standard model (MSSM) is replaced by $\lambda S$, where $S$ is a singlet field, leading to a Peccei-Quinn (PQ) symmetry. The axion becomes a heavy pseudoscalar, $G$, by adding a mass, $m_G$, by hand. The explicit breaking of PQ symmetry is assumed to be sufficiently weak at the TeV scale that the only observable consequence is the mass $m_G$. Three models for the explicit PQ breaking are given; but the utility of this framework is that the predictions for all physics at the electroweak scale are independent of the particular model for PQ breaking. This framework leads to a theory similar to the MSSM, except that $\mu$ is predicted by the Ciafaloni-Pomarol relation, and there are light, weakly-coupled states that lie dominantly in the superfield $S$. The production and cascade decay of superpartners at colliders occurs as in the MSSM, except that there is one extra stage of the cascade chain, with the next-to-LSP decaying to its superpartner and $\tilde{s}$, dramatically altering the collider signatures for supersymmetry. The framework is compatible with terrestrial experiments and astrophysical observations for a wide range of $m_G$ and $⟨s⟩$. If $G$ is as light as possible, $300\mathrm{k}\mathrm{e}\mathrm{V}<m_G<3\mathrm{M}\mathrm{e}\mathrm{V}$, it can have interesting effects on the radiation energy density during the cosmological eras of nucleosynthesis and acoustic oscillations, leading to predictions for $N_{\nu \mathrm{B}\mathrm{B}\mathrm{N}}$ and $N_{\nu \mathrm{C}\mathrm{M}\mathrm{B}}$ different from 3.

In previous studies we found that models with flavor-universal suppression of the neutrino-gauge couplings are compatible with NuTeV and $Z$-pole data. In this paper we expand our analysis to obtain constraints on flavor-dependent coupling suppression by including lepton universality data from $W$, $\tau$, $\pi$ and $K$ decays in fits to model parameters. We find that the data are consistent with a variety of patterns of coupling suppression. In particular, in scenarios in which the suppression arises from the mixing of light neutrinos with heavy gauge singlet states (neutrissimos), we find patterns of flavor-dependent coupling suppression which are also consistent with constraints from $\mu \to e\gamma$.

We have completed the evaluation of all mass-dependent ${\alpha }^4$ QED contributions to the muon $g-2$, or $a_{\mu }$, in two or more different formulations. Their numerical values have been greatly improved by an extensive computer calculation. The new value of the dominant ${\alpha }^4$ term $A_2^{(8)}(m_{\mu }/m_e)$ is 132.6823 (72), which supersedes the old value 127.50 (41). The new value of the three-mass term $A_3^{(8)}(m_{\mu }/m_e,m_{\mu }/m_{\tau })$ is 0.0376 (1). The term $A_2^{(8)}(m_{\mu }/m_{\tau })$ is crudely estimated to be about 0.005 and may be ignored for now. The total QED contribution to $a_{\mu }$ is $116584719.58(0.02)(1.15)(0.85)\times {10}^{-11}$, where 0.02 and 1.15 are uncertainties in the ${\alpha }^4$ and ${\alpha }^5$ terms and 0.85 is from the uncertainty in $\alpha$ measured by atom interferometry. This raises the standard model prediction by $13.9\times {10}^{-11}$, or about 1/5 of the measurement uncertainty of $a_{\mu }$. It is within the noise of current uncertainty ($\sim 100\times {10}^{-11}$) in the estimated hadronic contributions to $a_{\mu }$.

We present a quenched lattice QCD calculation of the $\alpha$ and $\beta$ parameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range $a\approx 0.1-0.064\mathrm{f}\mathrm{m}$ to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit, $|\alpha (\mathrm{N}\mathrm{D}\mathrm{R},2\mathrm{G}\mathrm{e}\mathrm{V})|=0.0090(09)(+5-19){\mathrm{G}\mathrm{e}\mathrm{V}}^3$ and $|\beta (\mathrm{N}\mathrm{D}\mathrm{R},2\mathrm{G}\mathrm{e}\mathrm{V})|=0.0096(09)(+6-20){\mathrm{G}\mathrm{e}\mathrm{V}}^3$ with $\alpha$ and $\beta$ in a relatively opposite sign, where the first error is statistical and the second is due to the uncertainty in the determination of the physical scale.

We derive the kinetic equation for fermions and antifermions interacting with a planar Higgs bubble wall during the electroweak phase transition using the “evenization” procedure. Equations of motion in a relativistic quantum theory do not mirror classical relations unless one uses evenized operators. We give a brief introduction to evenization and then use the evenized Heisenberg equations of motion to obtain the velocity and force for the particles in the presence of the Higgs bubble wall. Keeping quantum contributions to $O(\hslash )$ in the equations of motion, we obtain the semiclassical force obtained earlier by other techniques.

In this paper we study the question of residual gauge fixing in the path integral approach for a general class of axial-type gauges including the light-cone gauge. We show that the two cases—axial-type gauges and the light-cone gauge—lead to very different structures for the explicit forms of the propagator. In the case of the axial-type gauges, fixing the residual symmetry determines the propagator of the theory completely. On the other hand, in the light-cone gauge there is still a prescription dependence even after fixing the residual gauge symmetry, which is related to the existence of an underlying global as well as local symmetry.

We have recently argued that if one introduces a relational time in quantum mechanics and quantum gravity, the resulting quantum theory is such that pure states evolve into mixed states. The rate at which states decohere depends on the energy of the states. There is therefore the question of how this can be reconciled with Galilean invariance. More generally, since the relational description is based on objects that are not Dirac observables, the issue of covariance is of importance in the formalism as a whole. In this note we work out an explicit example of a totally constrained, generally covariant system of nonrelativistic particles that shows that the formula for the relational conditional probability is a Galilean scalar and therefore the decoherence rate is invariant.