Expectations for the momentum distribution of nonperturbative charm and bottom quarks in the proton are derived from a variety of models for the Fock space wave function on the light cone.

We describe a measurement of the top quark mass from events produced in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV, using the Collider Detector at Fermilab. We identify $t\overline{t}$ candidates where both $W$ bosons from the top quarks decay into leptons ($e\nu$, $\mu \nu$, or $\tau \nu$) from a data sample of $360{\mathrm{pb}}^{-1}$. The top quark mass is reconstructed in each event separately by three different methods, which draw upon simulated distributions of the neutrino pseudorapidity, $t\overline{t}$ longitudinal momentum, or neutrino azimuthal angle in order to extract probability distributions for the top quark mass. For each method, representative mass distributions, or templates, are constructed from simulated samples of signal and background events, and parametrized to form continuous probability density functions. A likelihood fit incorporating these parametrized templates is then performed on the data sample masses in order to derive a final top quark mass. Combining the three template methods, taking into account correlations in their statistical and systematic uncertainties, results in a top quark mass measurement of $170.1\pm 6.0(\mathrm{stat}.)\pm 4.1(\mathrm{syst}.)\mathrm{GeV}/c^2$.

We consider a benchmark bulk theory in four dimensions: $\mathcal{N}=2$ supersymmetric QCD with the gauge group $\mathrm{U}(N)$ and $N_f$ flavors of fundamental matter hypermultiplets (quarks). The nature of the Bogomol’nyi-Prasad-Sommerfield (BPS) strings in this benchmark theory crucially depends on $N_f$. If $N_f\ge N$ and all quark masses are equal, it supports non-Abelian BPS strings which have internal (orientational) moduli. If $N_f>N$ these strings become semilocal, developing additional moduli $\rho$ related to (unlimited) variations of their transverse size. Using the U(2) gauge group with $N_f=3$, 4 as an example, we derive an effective low-energy theory on the (two-dimensional) string world sheet. Our derivation is field theoretic, direct and explicit: we first analyze the Bogomol’nyi equations for string-geometry solitons, suggest an ansatz, and solve it at large $\rho$. Then we use this solution to obtain the world-sheet theory. In the semiclassical limit our result confirms the Hanany-Tong conjecture, which rests on brane-based arguments, that the world-sheet theory is an $\mathcal{N}=2$ supersymmetric U(1) gauge theory with $N$ positively and $N_e=N_f-N$ negatively charged matter multiplets and the Fayet-Iliopoulos term determined by the four-dimensional coupling constant. We conclude that the Higgs branch of this model is not lifted by quantum effects. As a result, such strings cannot confine. Our analysis of infrared effects, not seen in the Hanany-Tong consideration, shows that, in fact, the derivative expansion can make sense only provided that the theory under consideration is regularized in the infrared, e.g. by the quark mass differences. The world-sheet action discussed in this paper becomes a bona fide low-energy effective action only if $\Delta m_{AB}\ne 0$.

We consider a braneworld model in which an anisotropic brane is embedded in a dilatonic background. We find the background solutions and study the behavior of the perturbations when the universe evolves from an inflationary Kasner phase to a Minkowski phase. We calculate the massless mode spectrum, and find that it does not differ from what expected in standard four-dimensional cosmological models. We then evaluate the spectrum of both light (ultrarelativistic) and heavy (nonrelativistic) massive modes, and find that, at high energies, there can be a strong enhancement of the Kaluza-Klein spectral amplitude, which can become dominant in the total spectrum. The presence of the dilaton, on the contrary, decrease the relative importance of the massive modes.

As gravitational wave astronomy becomes a reality, issues of how to best combine and expand the global network of observatories will come to the fore. We have constructed several models to determine optimal additions to an existing global network of observatories for certain gravitational wave source populations and detection strategies.

It has recently been suggested that, in a brane-world scenario with large extra dimensions, short-distance gravitational interactions can enhance the dark matter scattering cross section in a velocity-dependent way. Such a modification may then help to address possible problems with noninteracting cold dark matter on galactic and subgalactic scales. We argue that, considering the singular character of the higher-dimensional Newtonian potential, the scattering cross section is UV dependent, depending ultimately on the underlying quantum gravity theory considered. We demonstrate that, for a wide class of unitary short-distance regularizations, the actual cross section is velocity independent and does not significantly affect the dark matter substructure. We comment on the problem of thermalization of ultralight cold dark matter by gravitational interactions in the early universe.

We show that the energy density spectrum of the primordial gravitational waves has characteristic features due to the successive changes in the relativistic degrees of freedom during the radiation era. These changes make the evolution of radiation energy density deviate from the conventional adiabatic evolution, ${\rho }_r\propto a^{-4}$, and thus cause the expansion rate of the universe to change suddenly at each transition which, in turn, modifies the spectrum of primordial gravitational waves. We take into account all the particles in the standard model of elementary particles. In addition, free-streaming of neutrinos damps the amplitude of gravitational waves, leaving characteristic features in the energy density spectrum. Our calculations are solely based on the standard model of cosmology and particle physics, and therefore these features must exist. Our calculations significantly improve the previous ones which ignored these effects and predicted a smooth, featureless spectrum.

We give a numerical analysis of long-wavelength modes in the WKB approximation of cosmological scalar fields coupled to gravity via $\xi {\varphi }^{2}R$. Massless fields are coupled conformally at $\xi =1/6$. Conformality can be preserved for fields of nonzero mass by shifting $\xi$. We discuss implications for density perturbations.

A fifth force, of technicolor type, responsible for breaking the electroweak theory is an intriguing extension of the standard model. Recently new theories have been shown to feature walking dynamics for a very low number of techniflavors and are not ruled out by electroweak precision measurements. We identify the light degrees of freedom and construct the associated low energy effective theories. These can be used to study signatures and relevant processes in current and future experiments. In our theory the technibaryons are pseudo Goldstone bosons and their masses arise via extended technicolor interactions. There are hypercharge assignments for the techniquarks which renders one of the technibaryons electrically neutral. We investigate the cosmological implications of this scenario and provide a component of dark matter.

We discuss the extraction of the electromagnetic and spin polarizabilities of nucleons from lattice QCD. We show that the external field method can be used to measure all the electromagnetic and spin polarizabilities including those of charged particles. We then turn to the extrapolations required to connect such calculations to experiment in the context of finite volume chiral perturbation theory. We derive results relevant for lattice simulations of QCD, partially-quenched QCD and quenched QCD. Our results for the polarizabilities show a strong dependence on the lattice volume and quark masses, typically differing from the infinite volume limit by $\sim 10\%$ for current lattice volumes and quark masses.

We apply twisted boundary conditions to lattice QCD simulations of three-point correlation functions in order to access spatial components of hadronic momenta different from the integer multiples of $2\pi /L$. We calculate the vector and scalar form factors relevant to the $K\to \pi$ semileptonic decay and consider all the possible ways of twisting one of the quark lines in the three-point functions. We show that the momentum shift produced by the twisted boundary conditions does not introduce any additional noise and easily allows us to determine within a few percent of statistical accuracy the form factors at quite small values of the four-momentum transfer, which are not accessible when periodic boundary conditions are considered. The use of twisted boundary conditions turns out to be crucial for a precise determination of the form factor at zero-momentum transfer, when a precise lattice point sufficiently close to zero-momentum transfer is not accessible with periodic boundary conditions.

We point out that the $B\to \rho \rho$ data have seriously constrained the possibility of resolving the $B\to \pi \pi$ puzzle from the large observed $B^0\to {\pi }^0{\pi }^0$ branching ratio in the available theoretical approaches. The next-to-leading-order (NLO) contributions from the vertex corrections, the quark loops, and the magnetic penguin evaluated in the perturbative QCD (PQCD) approach have saturated the experimental upper bound of the $B^0\to {\rho }^0{\rho }^0$ branching ratio and do not help. The NLO PQCD predictions for the $B^0\to {\rho }^{\mp }{\rho }^{\pm }$ and $B^{\pm }\to {\rho }^{\pm }{\rho }^0$ branching ratios are consistent with the data. The inclusion of the NLO jet function from the soft-collinear effective theory into the QCD-improved factorization approach, though enhancing the $B^0\to {\pi }^0{\pi }^0$ branching ratio sufficiently, overshoots the bound of the $B^0\to {\rho }^0{\rho }^0$ branching ratio and deteriorates the predictions for the $B^{\pm }\to {\pi }^0{K}^{\pm }$ and $B^0\to {\pi }^{\mp }{K}^{\pm }$ direct $CP$ asymmetries.

We discuss the higher Fock-state ($q\overline{q}g$) contributions to the nonzero value of the pion generalized parton distribution (GPD) at the crossover point $x=\zeta$ between the DGLAP and ERBL regions. Using the phenomenological light-front constituent quark model, we confirm that the higher Fock-state contributions indeed give a nonzero value of the GPD at the crossover point. Iterating the light-front quark model wave function of the lowest $q\overline{q}$ Fock state with the Bethe-Salpeter kernel corresponding to the one-gluon exchange, we include all possible time-ordered $q\overline{q}g$ Fock-state contributions and obtain the pion GPD satisfying necessary sum rules and continuity conditions.

We analyze the constraints on neutrino mass spectra with extra sterile neutrinos as implied by the LSND experiment. The various mass related observables in neutrinoless double beta decay, tritium beta decay and cosmology are discussed. Both neutrino oscillation results as well as recent cosmological neutrino mass bounds are taken into account. We find that some of the allowed mass patterns are severely restricted by the current constraints, in particular, by the cosmological constraints on the total sum of neutrino masses and by the nonmaximality of the solar neutrino mixing angle. Furthermore, we estimate the form of the four neutrino mass matrices and also comment on the situation in scenarios with two additional sterile neutrinos.

We study the geometry of M5-branes wrapping a 2-cycle which is special Lagrangian with respect to a specific complex structure in a Calabi-Yau 2-fold. Using methods recently applied to the 3-fold case, we are again able to find a characterization of the geometry, in terms of a nonintegrable almost complex structure and a (2,0) form. This time, however, due to the hyper-Kähler nature of the underlying 2-fold, we also have the freedom of choosing a different almost complex structure with respect to which the wrapped 2-cycle is holomorphic. We show that this latter almost complex structure is integrable. We then relate our geometry to previously found geometries of M5-branes wrapping holomorphic cycles and go further to prove some previously unknown results for M5-branes on holomorphic cycles.

We address two distinct but related issues: (i) the impact of (two-dimensional) axions in a two-dimensional theory known to model confinement, the $CP(N-1)$ model; (ii) bulk axions in four-dimensional Yang-Mills theory supporting non-Abelian strings. In the first case $n$, $\overline{n}$ kinks play the role of “quarks.” They are known to be confined. We show that introduction of axions leads to deconfinement (at very large distances). This is akin to the phenomenon of wall liberation in four-dimensional Yang-Mills theory. In the second case we demonstrate that the bulk axion does not liberate confined (anti)monopoles, in contradistinction with the two-dimensional model. A novel physical effect which we observe is the axion radiation caused by monopole-antimonopole pairs attached to the non-Abelian strings.

A holographic model of QCD at finite temperature is proposed and thermal properties for light mesons are examined in terms of this model. We find interesting temperature dependences of masses and decay constants for several mesons, and the Nambu-Goldstone theorem for the chiral symmetry breaking and the generalized Gell-Mann-Oakes-Renner relation are assured at finite temperature. In the chiral limit, the speed of a pion in the thermal medium is found to decrease as temperature increases to the critical temperature of quark confinement-deconfinement transition.

We investigate how classical predictability of the coarse-grained evolution of the quantum baker’s map depends on the character of the coarse-graining. Our analysis extends earlier work by Brun and Hartle [Phys. Rev. D 60, 123503 (1999)] to the case of a chaotic map. To quantify predictability, we compare the rate of entropy increase for a family of coarse-grainings in the decoherent histories formalism. We find that the rate of entropy increase is dominated by the number of scales characterizing the coarse-graining.

A systematic method to obtain the effective Lagrangian on the Bogomol’nyi-Prasad-Sommerfield background in supersymmetric gauge theories is worked out, taking domain walls and vortices as concrete examples. The Lagrangian in terms of the superfields with four preserved supercharges is expanded in powers of the slow-movement parameter $\lambda$. The expansion gives the superfield form of the Bogomol’nyi-Prasad-Sommerfield equations at $\mathcal{O}({\lambda }^0)$, and all the fluctuation fields at $\mathcal{O}({\lambda }^1)$. The density of the Kähler potential for the effective Lagrangian follows as an automatic consequence of the $\lambda$ expansion making (four preserved) supercharges manifest.

The Mathisson-Papapetrou method is originally used for derivation of the particle world line equation from the covariant conservation of its stress-energy tensor. We generalize this method to extended objects, such as a string. Without specifying the type of matter the string is made of, we obtain both the equations of motion and boundary conditions of the string. The world sheet equations turn out to be more general than the familiar minimal surface equations. In particular, they depend on the internal structure of the string. The relevant cases are classified by examining canonical forms of the effective 2-dimensional stress-energy tensor. The case of homogeneously distributed matter with the tension that equals its mass density is shown to define the familiar Nambu-Goto dynamics. The other three cases include physically relevant massive and massless strings, and unphysical tachyonic strings.