Using the WKBJ approximation and the Unruh method, we obtain semi-analytic expressions for the absorption probability (in all energy regimes) for Dirac fermions on a higher dimensional Schwarzschild background. We then present an analytic expression relating the absorption probability to the absorption cross section, and then use these results to plot the emission rates to third order in the WKBJ approximation. The setup we use is sufficiently general such that it could also easily be applied to any spherically symmetric background in $d$ dimensions. Our results lead to the interesting conclusion that for $d>5$ bulk fermion emission dominates brane-localized emission. This is an example contrary to the conjecture that black holes radiate mainly on the brane.

A mechanism for the enhancement for proton lifetime in supersymmetric/supergravity (SUSY/SUGRA) grand unified theories and in string theory models is discussed where Higgsino mediated proton decay arising from color triplets (antitriplets) with charges $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ is suppressed by an internal cancellation due to contributions from different sources. We exhibit the mechanism for an $SU(5)$ model with ${45}_H+{\overline{45}}_H$ Higgs multiplets in addition to the usual Higgs structure of the minimal model. This model contains both $Q=-1/3(1/3)$ and $Q=-4/3(4/3)$ Higgs color triplets (antitriplets) and simple constraints allow for a complete suppression of Higgsino mediated proton decay. Suppression of proton decay in an $SU(5)$ model with Planck scale contributions is also considered. The suppression mechanism is then exhibited for an $SO(10)$ model with a unified Higgs structure involving ${144}_H+{\overline{144}}_H$ representations. The $SU(5)$ decomposition of ${144}_H+{\overline{144}}_H$ contains $5_H+{\overline{5}}_H$ and ${45}_H+{\overline{45}}_H$ and the cancellation mechanism arises among these contributions which mirror the $SU(5)$ case. The cancellation mechanism appears to be more generally valid for a larger class of unification models. Specifically the cancellation mechanism may play a role in string model constructions to suppress proton decay from dimension five operators. The mechanism allows for the suppression of proton decay consistent with current data allowing for the possibility that proton decay may be visible in the next round of nucleon stability experiment.

We present the near light cone Hamiltonian $H$ in lattice QCD depending on the parameter $\eta$, which gives the distance to the light cone. Since the vacuum has zero momentum we can derive an effective Hamiltonian $H_{\mathrm{eff}}$ from $H$ which is only quadratic in the momenta and therefore solvable by standard methods. An approximate ground state wave functional is determined variationally in the limit $\eta \to 0$.

We consider the response of the QCD ground state at finite baryon density to a strong magnetic field $B$. We point out the dominant role played by the coupling of neutral Goldstone bosons, such as ${\pi }^0$, to the magnetic field via the axial triangle anomaly. We show that, in vacuum, above a value of $B\sim m_{\pi }^2/e$, a metastable object appears—the ${\pi }^0$ domain wall. Because of the axial anomaly, the wall carries a baryon number surface density proportional to $B$. As a result, for $B\gtrsim {10}^{19}\mathrm{G}$ a stack of parallel ${\pi }^0$ domain walls is energetically more favorable than nuclear matter at the same density. Similarly, at higher densities, somewhat weaker magnetic fields of order $B\gtrsim {10}^{17}–{10}^{18}\mathrm{G}$ transform the color-superconducting ground state of QCD into new phases containing stacks of axial isoscalar ($\eta$ or ${\eta }^{\prime }$) domain walls. We also show that a quark-matter state known as “Goldstone current state,” in which a gradient of a Goldstone field is spontaneously generated, is ferromagnetic due to the axial anomaly. We estimate the size of the fields created by such a state in a typical neutron star to be of order ${10}^{14}–{10}^{15}\mathrm{G}$.

In this work we investigate the weak ${\Lambda }_b\to {\Lambda }_c$ semileptonic and nonleptonic decays. The light-front quark model and diquark picture for heavy baryons are adopted to evaluate the ${\Lambda }_b\to {\Lambda }_c$ transition form factors. In the heavy quark limit we study the Isgur-Wise function. The transition form factors are obtained in the whole physical momentum regions. The numerical predictions on the branching ratios of nonleptonic decay modes ${\Lambda }_b\to {\Lambda }_{c}M$ and various polarization asymmetries are made. A comparison with other approaches is discussed.

We present a measurement of the muon charge asymmetry from $W$ boson decays using $0.3{\mathrm{fb}}^{-1}$ of data collected at $\sqrt{s}=1.96\mathrm{GeV}$ between 2002 and 2004 with the D0 detector at the Fermilab Tevatron $p\overline{p}$ Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.

An algorithm recently presented by Lake to obtain all static spherically symmetric perfect fluid solutions is extended to the case of locally anisotropic fluids (principal stresses unequal). As expected, the new formalism requires the knowledge of two functions (instead of one) to generate all possible solutions. To illustrate the method some known cases are recovered.

We construct generalized 11D supergravity solutions of fully localized intersecting D2/D4 brane systems. These solutions are obtained by embedding six-dimensional resolved Eguchi-Hanson conifolds lifted to M-theory. We reduce these solutions to ten dimensions, obtaining new D-brane systems in type IIA supergravity. We discuss the limits in which the dynamics of the D2 brane decouples from the bulk for these solutions.

Twisted quantum field theories on the Groenewold-Moyal plane are known to be nonlocal. Despite this nonlocality, it is possible to define a generalized notion of causality. We show that interacting quantum field theories that involve only couplings between matter fields, or between matter fields and minimally coupled $U(1)$ gauge fields are causal in this sense. On the other hand, interactions between matter fields and non-Abelian gauge fields violate this generalized causality. We derive the modified Feynman rules emergent from these features. They imply that interactions of matter with non-Abelian gauge fields are not Lorentz- and $CPT$-invariant.

We present techniques for long-term, stable, and accurate evolutions of multiple-black-hole spacetimes using the “moving puncture” approach with fourth- and eighth-order finite-difference stencils. We use these techniques to explore configurations of three black holes in a hierarchical system consisting of a third black hole approaching a quasicircular black-hole binary, and find that, depending on the size of the binary, the resulting encounter may lead to a prompt merger of all three black holes, production of a highly elliptical binary (with the third black hole remaining unbound), or disruption of the binary (leading to three free black holes). We also analyze the classical Burrau three-body problem using full numerical evolutions. In both cases, we find behaviors distinctly different from Newtonian predictions, which has important implications for N-body black-hole simulations. For our simulations we use approximate analytic initial data. We find that the eighth-order stencils significantly reduce the numerical errors for our choice of grid sizes, and that the approximate initial data produces the expected waveforms for black-hole binaries with modest initial separations.

It has long been known that there is a relation between boundary sine-Gordon theory and thermodynamics of charge neutral two-component Coulomb plasma on a unit circle. On the other hand, recently it was found that open string world sheet description of brane decay can be related to a sequence of points of thermodynamic equilibrium of one-component plasma. Here we consider a different decay process which is specifically described by the timelike boundary sine-Gordon theory. We find time evolution to be mapped to a one-dimensional curve in the space of points of thermal equilibrium of a non-neutral two-component Coulomb plasma. We compute the free energy of the system and find that along the curve it is monotonically decreasing, defining a thermodynamic arrow of time.

We explore the stability properties of multifield solutions of assisted inflation type, where several fields collectively evolve to the same configuration. In the case of noninteracting fields, we show that the condition for such solutions to be stable is less restrictive than that required for tracking in quintessence models. Our results, which do not rely on the slow-roll approximation, further indicate that to linear order in homogeneous perturbations the fields are in fact unaware of each other’s existence. We end by generalizing our results to some cases of interacting fields and to other background solutions and dynamics, including the high-energy braneworld.

Ground-based gravitational wave detectors may be able to constrain the nuclear equation of state using the early, low frequency portion of the signal of detected neutron star–neutron star inspirals. In this early adiabatic regime, the influence of a neutron star’s internal structure on the phase of the waveform depends only on a single parameter $\lambda$ of the star related to its tidal Love number, namely, the ratio of the induced quadrupole moment to the perturbing tidal gravitational field. We analyze the information obtainable from gravitational wave frequencies smaller than a cutoff frequency of 400 Hz, where corrections to the internal-structure signal are less than 10%. For an inspiral of two nonspinning $1.4M_{\odot }$ neutron stars at a distance of 50 Megaparsecs, LIGO II detectors will be able to constrain $\lambda$ to $\lambda \le 2.0\times {10}^{37}\mathrm{g}{\mathrm{cm}}^2{\mathrm{s}}^2$ with 90% confidence. Fully relativistic stellar models show that the corresponding constraint on radius $R$ for $1.4M_{\odot }$ neutron stars would be $R\le 13.6\mathrm{km}$ (15.3 km) for a $n=0.5$ ($n=1.0$) polytrope with equation of state $p\propto {\rho }^{1+1/n}$.

It is proposed that fragmentation functions should be used to identify exotic hadrons. As an example, fragmentation functions of the scalar meson $f_0(980)$ are investigated. It is pointed out that the second moments and functional forms of the $u$- and $s$-quark fragmentation functions can distinguish the tetraquark structure from $q\overline{q}$. By the global analysis of $f_0(980)$ production data in electron-positron annihilation, its fragmentation functions and their uncertainties are determined. It is found that the current available data are not sufficient to determine its internal structure, while precise data in the future should be able to identify exotic quark configurations.

It has been argued by Pisarski and Wilczek that finite temperature restoration of $\mathrm{SU}(N_f)\times \mathrm{SU}(N_f)$ chiral symmetry is first order for $N_f\ge 3$. This type of chiral symmetry with large $N_f$ may appear in the Higgs sector if one considers models such as walking technicolor theories. We examine the first-order restoration of chiral symmetry from the point of view of the electroweak phase transition. The strength of the transition is estimated in a $\mathrm{SU}(2)\times \mathrm{U}(1)$ gauged linear sigma model by means of the finite temperature effective potential at one loop with the ring improvement. Even if the mass of the neutral scalar boson corresponding to the Higgs boson is larger than 114 GeV, the first-order transition can be strong enough for electroweak baryogenesis, as long as the extra massive scalar bosons (required for the linear realization) are kept heavier than the neutral scalar boson. Explicit symmetry breaking terms reduce the strength of the first-order transition, but the transition can remain strongly first order even when the masses of pseudo Nambu-Goldstone bosons become as large as the current lower bound of direct search experiments.

We study scenarios in the minimal and next-to-minimal supersymmetric models in which the lightest $CP$-even Higgs boson can have mass below the 114 GeV standard model LEP limit by virtue of reduced $ZZ$ coupling due to substantial mixing among the Higgs bosons. We pay particular attention to the size of corrections from superpartners needed for these scenarios to be viable and point to boundary conditions at large scales which lead to these scenarios while at the same time keeping electroweak fine-tuning modest in size. We find that naturalness of electroweak symmetry breaking in the mixed-Higgs scenarios of both models points to the same region of soft supersymmetry breaking terms as in the decoupled scenarios with mass of the $CP$ even Higgs boson above 114 GeV, namely those leading to large mixing in the stop sector at the electroweak scale, especially if we also require that the lightest $CP$-even Higgs explains the Higgs-like LEP events at $\sim 98\mathrm{GeV}$.

We present results on the equation of state in QCD with two light quark flavors and a heavier strange quark. Calculations with improved staggered fermions have been performed on lattices with temporal extent $N_{\tau }=4$ and 6 on a line of constant physics with almost physical quark mass values; the pion mass is about 220 MeV, and the strange quark mass is adjusted to its physical value. High statistics results on large lattices are obtained for bulk thermodynamic observables, i.e. pressure, energy and entropy density, at vanishing quark chemical potential for a wide range of temperatures, $140\mathrm{MeV}\le T\le 800\mathrm{MeV}$. We present a detailed discussion of finite cutoff effects which become particularly significant for temperatures larger than about twice the transition temperature. At these high temperatures we also performed calculations of the trace anomaly on lattices with temporal extent $N_{\tau }=8$. Furthermore, we have performed an extensive analysis of zero temperature observables including the light and strange quark condensates and the static quark potential at zero temperature. These are used to set the temperature scale for thermodynamic observables and to calculate renormalized observables that are sensitive to deconfinement and chiral symmetry restoration and become order parameters in the infinite and zero quark mass limits, respectively.

We analyze the determination of volume effects for correlation functions that depend on an external momentum. As a specific example, we consider finite volume nucleon current correlators, and focus on the nucleon magnetic moment. Because the multipole decomposition relies on $SO(3)$ rotational invariance, the structure of such finite volume corrections is unrelated to infinite volume multipole form factors. One can deduce volume corrections to the magnetic moment only when a zero-mode photon coupling vanishes, as occurs at next-to-leading order in heavy baryon chiral perturbation theory. To deduce such finite volume corrections, however, one must assume continuous momentum transfer. In practice, volume corrections with momentum transfer dependence are required to address the extraction of the magnetic moment, or other observables that arise in momentum-dependent correlation functions. Additionally, we shed some light on a puzzle concerning differences in lattice form factor data at equal values of momentum transfer squared.

We present results for the dependence of the residual mass of domain wall fermions on the size of the fifth dimension and its relation to the density and localization properties of low-lying eigenvectors of the corresponding Hermitian Wilson Dirac operator in three flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate ensembles of configurations with a ${16}^3\times 32$ space-time volume and an extent of 8 in the fifth dimension for the sea quarks. We demonstrate the existence of a regime where the degree of locality, the size of chiral symmetry breaking, and the rate of topology change can be acceptable for inverse lattice spacings $a^{-1}\ge 1.6\mathrm{GeV}$, enabling a programme of simulations of $2+1$ flavor QCD to be conducted safely in this region of parameter space.

The small-$x$ deep inelastic scattering in the saturation region is governed by the nonlinear evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the Balitsky-Kovchegov equation for the evolution of color dipoles. In the next-to-leading order the Balitsky-Kovchegov equation gets contributions from quark and gluon loops as well as from the tree gluon diagrams with quadratic and cubic nonlinearities. We calculate the gluon contribution to the small-$x$ evolution of Wilson lines (the quark part was obtained earlier).