We report the first measurement of the top quark mass using the decay length technique in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV. This technique uses the measured flight distance of the $b$ hadron to infer the mass of the top quark in lepton plus jets events with missing transverse energy. It relies solely on tracking and avoids the jet energy scale uncertainty that is common to all other methods used so far. We apply our novel method to a $695{\mathrm{pb}}^{-1}$ data sample recorded by the CDF II detector at Fermilab and extract a measurement of $m_t={180.7}_{-13.4}^{+15.5}(\mathrm{stat}.)\pm 8.6(\mathrm{syst}.)\mathrm{GeV}/c^2$. While the uncertainty of this result is larger than that of other measurements, the dominant uncertainties in the decay length technique are uncorrelated with those in other methods. This result can help reduce the overall uncertainty when combined with other existing measurements of the top quark mass.

Effects of neutrino free streaming are evaluated on the primordial spectrum of gravitational radiation taking both neutrino chemical potential and masses into account. The former or the lepton asymmetry induces two competitive effects, namely, to increase anisotropic stress, which damps the gravitational wave more, and to delay the matter-radiation equality time, which reduces the damping. The latter effect is more prominent and a large lepton asymmetry would reduce the damping. We may thereby be able to measure the magnitude of lepton asymmetry from the primordial gravitational wave spectrum.

Recently new Einstein-Yang-Mills (EYM) soliton solutions were presented which describe superconducting strings with Kasner asymptotics [D. V. Gal’tsov, E. A. Davydov, and M. S. Volkov, hep-th/0610183.]. Here we study the static cylindrically symmetric SU(2) EYM system in more detail. The ansatz for the gauge field corresponds to superposition of the azimuthal $B_{\phi }$ and the longitudinal $B_z$ components of the color magnetic field. We derive sum rules relating data on the symmetry axis to asymptotic data and show that generic asymptotic structure of regular solutions is Kasner. Solutions starting with vacuum data on the axis generically are divergent. Regular solutions correspond to some bifurcation manifold in the space of parameters which has the low-energy limiting point corresponding to string solutions in flat space (with the divergent total energy) and the high-curvature point where gravity is crucial. Some analytical results are presented for the low-energy limit, and numerical bifurcation curves are constructed in the gravitating case. Depending on the parameters, the solution looks like a straight string or a pair of straight and circular strings. The existence of such nonlinear superposition of two strings becomes possible due to self-interaction terms in the Yang-Mills action which suppress contribution of the circular string near the polar axis.

The dilaton-gravity sector of the two-measures field theory (TMT) is explored in detail in the context of spatially flat Friedman-Robertson-Walker (FRW) cosmology. The model possesses scale invariance which is spontaneously broken due to the intrinsic features of the TMT dynamics. The dilaton $\varphi$ dependence of the effective Lagrangian appears only as a result of the spontaneous breakdown of the scale invariance. If no fine-tuning is made, the effective $\varphi$-Lagrangian $p(\varphi ,X)$ depends quadratically upon the kinetic term $X$. Hence TMT represents an explicit example of the effective $k$-essence resulting from first principles without any exotic term in the underlying action intended for obtaining this result. Depending of the choice of regions in the parameter space (but without fine-tuning), TMT exhibits different possible outputs for cosmological dynamics: (a) Absence of initial singularity of the curvature while its time derivative is singular. This is a sort of sudden singularities studied by Barrow on purely kinematic grounds. (b) Power law inflation in the subsequent stage of evolution. Depending on the region in the parameter space the inflation ends with a graceful exit either into the state with zero cosmological constant (CC) or into the state driven by both a small CC and the field $\varphi$ with a quintessencelike potential. (c) Possibility of resolution of the old CC problem. From the point of view of TMT, it becomes clear why the old CC problem cannot be solved (without fine-tuning) in conventional field theories. (d) TMT enables two ways for achieving small CC without fine-tuning of dimensionful parameters: either by a seesaw type mechanism or due to a correspondence principle between TMT and conventional field theories (i.e. theories with only the measure of integration $\sqrt{-g}$ in the action). (e) There is a wide range of the parameters such that in the late time universe: the equation of state $w=p/\rho <-1$; $w$ asymptotically (as $t\to \infty$) approaches $-1$ from below; $\rho$ approaches a constant, the smallness of which does not require fine-tuning of dimensionful parameters.

The recent observation of the purely leptonic decay $B^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ at the $B$ factories permits a sizable contribution from a charged Higgs boson ($H^{\pm }$). Such a $H^{\pm }$ would also contribute to the decays $D_s^{\pm }\to {\mu }^{\pm }{\nu }_{\mu }$ and $D_s^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$, which are being measured with increasing precision at CLEO-c. We show that the branching ratios of $D_s^{\pm }\to {\mu }^{\pm }{\nu }_{\mu }$ and $D_s^{\pm }\to {\tau }^{\pm }{\nu }_{\tau }$ could be suppressed by up to 10% from the standard model prediction, which is larger than the anticipated precision in the measurements of these decays at forthcoming BES-III.

Time-odd parton distribution functions in a Drell-Yan process are here studied by examining the evolution of the internal statistical properties of the interacting hadrons. Time-odd functions are shown to be a signature of the irreversible process in which a hadronic state characterized by long range correlation properties (hadronic phase) decays to produce a cloud of independent partons (partonic phase) because of initial/final state interactions. The relevant considered variable is the rate of increase of the entropy of the hadronic system. This quantity is shown to be roughly equal to the decay rate of the hadronic state. Conditions for getting a leading twist time-odd effect are established on this basis. Last, the relevant case of a large entropy increase associated with transverse-dominated initial/final state interactions is analyzed.

We study the scaling regime of pion electroproduction in the backward region, $eN\to e^{\prime }{N}^{\prime }\pi$. We compute the leading-twist amplitude in the kinematical region, where it factorises into a short-distance matrix element and long-distance dominated nucleon distribution amplitudes and nucleon to pion transition distribution amplitudes. Using the chiral limit of the latter, we obtain a first estimate of the cross section, which may be experimentally studied at JLab or Hermes.

The process of pair creation by a photon in a strong magnetic field is investigated based on the polarization operator in the field. The total probability of the process is calculated in a relatively simple form using an adequate method. The new results are obtained in the scope of the quasiclassical approach in the case when the magnetic field $B\ll B_0$ ($B_0$ is the critical field). This is the new formulation of the approach which extends its validity to the case when the created particles are not ultrarelativistic. The correction to the standard quasiclassical approximation is found as well, showing the range of applicability of the approach at high photon energy. The very important conclusion is that, for both cases $B\ll B_0$ and $B\ge B_0$, the results of the quasiclassical calculation are very close to averaged probabilities of exact theory in a very wide range of photon energies. The quasiclassical approximation is valid also for the energy distribution if the electron and the positron are created on high enough levels even for $B\ge B_0$.

The same light-front wave functions of the proton are involved in both the anomalous magnetic moment of the nucleon and the Sivers function. Using the diquark model, we derive a simple relation between the anomalous magnetic moment and the Sivers function, which should hold in general with good approximation. This relation can be used to provide constraints on the Sivers single spin asymmetries from the data on anomalous magnetic moments. Moreover, the relation can be viewed as a direct connection between the quark orbital angular momentum and the Sivers function.

Using the general QCD parametrization (GP) we display the magnetic moments of the octet baryons including all flavor breaking terms to any order. The hierarchy of the GP parameters allows to estimate a parameter $g_0$ related to the quark loops contribution of the proton magnetic moment; its magnitude is predicted to be inside a comparatively small interval including the value given recently by Leinweber et al. from a lattice QCD calculation.

Here we respond to the comment by Tsagas on our earlier paper. We show that the results in that comment are flawed and cannot be used for drawing conclusions about the nature of magnetic field amplification by gravitational waves and give further support that the results of our earlier paper are correct.

We consider the amplification of cosmological magnetic fields by gravitational waves as it was recently presented by Betschart et al. That study confined to infinitely conductive environments, arguing that on spatially flat Friedmann backgrounds the gravito-magnetic interaction proceeds always as if the Universe were a perfect conductor. We explain why this claim is not correct and then reexamine the Maxwell-Weyl coupling at the limit of ideal magnetohydrodynamics. We find that the scales of the main results of Betschart et al. were not properly assessed and that the incorrect scale assessment has compromised both the physical and the numerical results of the paper. This comment aims to clarify these issues on the one hand, while on the other it takes a closer look at the gauge invariance and the nonlinearity of the formalism proposed by Betschart et al.

We propose the general scheme of incorporation of the Dirac monopoles into mechanical systems on the three-dimensional conformal flat space. We found that any system (without monopoles) admitting the separation of variables in the elliptic or parabolic coordinates can be extended to the integrable system with the Dirac monopoles located at the foci of the corresponding coordinate systems. Particular cases of this class of system are the two-center MICZ-Kepler system in the Euclidean space, the limiting case when one of the background dyons is located at the infinity as well as the model of particle in parabolic quantum dot in the presence of parallel constant uniform electric and magnetic fields.

In this article we study the influence of magnetic fields on the axial gravitational waves emitted during the collapse of a homogeneous dust sphere. We found that while the energy emitted depends weakly on the initial matter perturbations it has strong dependence on the strength and the distribution of the magnetic field perturbations. The gravitational wave output of such a collapse can be up to an order of magnitude larger or smaller calling for detailed numerical 3D studies of collapsing magnetized configurations.

Corrections are computed to the classical static isotropic solution of general relativity, arising from nonperturbative quantum gravity effects. A slow rise of the effective gravitational coupling with distance is shown to involve a genuinely nonperturbative scale, closely connected with the gravitational vacuum condensate, and thereby related to the observed effective cosmological constant. We argue that in contrast to phenomenological approaches, the underlying functional integral formulation of the theory severely constrains possible scenarios for the renormalization group evolution of couplings. The general analysis is extended here to a set of covariant nonlocal effective field equations, intended to incorporate the full scale dependence of $G$, and examined in the case of the static isotropic metric. We find that the existence of vacuum solutions to the effective field equations in general severely restricts the possible values of the scaling exponent $\nu$.

We obtain two new classes of magnetic solutions in third order Lovelock gravity. The first class of solutions yields an ($n+1$)-dimensional spacetime with a longitudinal magnetic field generated by a static source. We generalize this class of solutions to the case of spinning magnetic strings with one or more rotation parameters. These solutions have no curvature singularity and no horizons, but have a conic geometry. For the spinning string, when one or more rotation parameters are nonzero, the string has a net electric charge which is proportional to the magnitude of the rotation parameters, while the static string has no net electric charge. The second class of solutions yields a spacetime with an angular magnetic field. These solutions have no curvature singularity, no horizon, and no conical singularity. Although the second class of solutions may be made electrically charged by a boost transformation, the transformed solutions do not present new spacetimes. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes.

We derive the conditions under which dark energy models whose Lagrangian densities $f$ are written in terms of the Ricci scalar $R$ are cosmologically viable. We show that the cosmological behavior of $f(R)$ models can be understood by a geometrical approach consisting of studying the $m(r)$ curve on the $(r,m)$ plane, where $m\equiv R{f}_{,RR}/f_{,R}$ and $r\equiv -R{f}_{,R}/f$ with $f_{,R}\equiv \mathrm{d}f/\mathrm{d}R$. This allows us to classify the $f(R)$ models into four general classes, depending on the existence of a standard matter epoch and on the final accelerated stage. The existence of a viable matter-dominated epoch prior to a late-time acceleration requires that the variable $m$ satisfies the conditions $m(r)\approx +0$ and $\mathrm{d}m/\mathrm{d}r>-1$ at $r\approx -1$. For the existence of a viable late-time acceleration we require instead either (i) $m=-r-1$, $(\sqrt{3}-1)/2<m\le 1$ and $\mathrm{d}m/\mathrm{d}r<-1$ or (ii) $0<m\le 1$ at $r=-2$. These conditions identify two regions in the $(r,m)$ space, one for the matter era and the other for the acceleration. Only models with an $m(r)$ curve that connects these regions and satisfies the requirements above lead to an acceptable cosmology. The models of type $f(R)=\alpha R^{-n}$ and $f=R+\alpha R^{-n}$ do not satisfy these conditions for any $n>0$ and $n<-1$ and are thus cosmologically unacceptable. Similar conclusions can be reached for many other examples discussed in the text. In most cases the standard matter era is replaced by a cosmic expansion with scale factor $a\propto t^{1/2}$. We also find that $f(R)$ models can have a strongly phantom attractor but in this case there is no acceptable matter era.

An exactly solvable bounce model in loop quantum cosmology is identified which serves as a perturbative basis for realistic bounce scenarios. Its bouncing solutions are derived analytically, demonstrating why recent numerical simulations robustly led to smooth bounces under the assumption of semiclassicality. Several effects, easily included in a perturbative analysis, can however change this smoothness. The effective theory is not only applicable to such situations where numerical techniques become highly involved but also allows one to discuss conceptual issues. For instance, consequences of the notoriously difficult physical inner product can be implemented at the effective level. This indicates that even physical predictions from full quantum gravity can be obtained from perturbative effective equations.

We give an assessment of the three approaches, undertaken by the D0 experiment, to probe $CP$ violation in $B_s$ mixing without measurement of $B_s\mathrm{\text{−}}{\overline{B}}_s$ oscillations or tagging: dimuon charge asymmetry $A_{SL}$, untagged single muon charge asymmetry $A_{SL}^s$, and lifetime difference in untagged $B_s\to J/\psi \varphi$ decay. The latter two approaches provide an alternative avenue, if not cross-check, to the usual mixing-decay interference study in modes such as $B_s\to J/\psi \varphi$. Prospects at the Tevatron, LHC, and (super) $B$ factories are discussed.

We study Polyakov loop correlations and spatial Wilson loop at finite temperature in two-flavor QCD simulations with the RG-improved gluon action and the clover-improved Wilson quark action on a ${16}^3\times 4$ lattice. From the line of constant physics at $m_{\mathrm{PS}}/m_{\mathrm{V}}=0.65$ and 0.80, we extract the heavy-quark free energies, the effective running coupling $g_{\mathrm{eff}}(T)$ and the Debye screening mass $m_D(T)$ for various color channels of heavy quark-quark and quark-antiquark pairs above the critical temperature. The free energies are well approximated by the screened Coulomb form with the appropriate Casimir factors at high temperature. The magnitude and the temperature dependence of the Debye mass are compared to those of the next-to-leading-order thermal perturbation theory and to a phenomenological formula in terms of $g_{\mathrm{eff}}(T)$. We make a comparison between our results with the Wilson quark action and the previous results with the staggered quark action. The spatial string tension is also studied in the high temperature phase and is compared to the next-to-next-leading-order prediction in an effective theory with dimensional reduction.