We study the spin polarizations of both $\tau$ leptons in the decay $\overrightarrow{b}s{\tau }^{+}{\tau }^{-}.$ In addition to the polarization asymmetries involving a single $\tau ,$ we construct asymmetries for the case where both polarizations are simultaneously measured. We also study forward-backward asymmetries with polarized $\tau$’s. We find that a large number of asymmetries are predicted to be large, $\gtrsim 10\%.$ This permits the measurement of all Wilson coefficients and the b-quark mass, thus allowing the standard model (SM) to be exhaustively tested. Furthermore, there are many unique signals for the presence of new physics. For example, asymmetries involving triple-product correlations are predicted to be tiny within the SM, ${O(10\mathrm{}}^{-2}).\mathrm{}$ Their observation would be a clear signal of new physics.

The path integral formulation is given to obtain quark and antiquark distribution functions in the nucleon within the flavor SU(3) version of the chiral quark soliton model. The basic model action is a straightforward generalization of the corresponding SU(2) one, except for one distinguishable feature, i.e., the presence of the SU(3) symmetry breaking term arising from the sizably large mass difference $\Delta m_s$ between the strange and nonstrange quarks. We treat this SU(3) symmetry breaking effect by relying upon the first-order perturbation theory in the mass parameter $\Delta m_s.$ We also address the problem of the ordering ambiguity of the relevant collective space operators, which arises in the evaluation of the parton distribution functions at the subleading order of the ${1/N}_c$ expansion.

Theoretical predictions are given for the light-flavor sea-quark distributions in the nucleon including the strange quark ones on the basis of the flavor SU(3) version of the chiral quark soliton model. Careful account is taken of the SU(3) symmetry breaking effects due to the mass difference $\Delta m_s$ between the strange and nonstrange quarks, which is the only one parameter necessary for the flavor SU(3) generalization of the model. A particular emphasis of study is put on the light-flavor sea-quark asymmetry as exemplified by the observables $\overline{d}\mathrm{}\left(x\right)\mathrm{}-ū\mathrm{}\left(x\right),\overline{d}\mathrm{}\left(x\right)/ū\mathrm{}\left(x\right),\Delta ū\mathrm{}\left(x\right)\mathrm{}-\Delta \overline{d}\mathrm{}\left(x\right)\mathrm{}$ as well as on the particle-antiparticle asymmetry of the strange quark distributions represented by $s\left(x\right)\mathrm{}-\overline{s}\mathrm{}\left(x\right),s\left(x\right)/\overline{s}\mathrm{}\left(x\right),\Delta s\left(x\right)\mathrm{}-\Delta \overline{s}\mathrm{}\left(x\right)\mathrm{}$ etc. As for the unpolarized sea-quark distributions, the predictions of the model seem qualitatively consistent with the available phenomenological information provided by the NMC data for $\overline{d}\mathrm{}\left(x\right)\mathrm{}-ū\mathrm{}\left(x\right),$ the E866 data for $\overline{d}\mathrm{}\left(x\right)/ū\mathrm{}\left(x\right),$ the CCFR data and the fit of Barone et al. for $s\left(x\right)/\overline{s}\mathrm{}\left(x\right),$ etc. The model is shown to give several unique predictions also for the spin-dependent sea-quark distribution, such that $\Delta s\left(x\right)\mathrm{}\ll \Delta \overline{s}\mathrm{}\left(x\right)\mathrm{}\lesssim 0$ and $\Delta \overline{d}\mathrm{}\left(x\right)<0<\Delta ū\mathrm{}\left(x\right),$ although the verification of these predictions must await more elaborate experimental investigations in the near future.

We calculate the conversion rate of high-energy neutrinos propagating in a constant magnetic field into an electron-$W$ pair $(\overrightarrow{\nu }W+e)$ from the imaginary part of the neutrino self-energy. Using the exact propagators in a constant magnetic field, the neutrino self-energy has been calculated to all orders in the field within the Weinberg-Salam model. We obtain a compact formula in the limit of $B\ll B_{\mathrm{cr}}\equiv m^2/e.\mathrm{}$ We find that above the process threshold $E^{\mathrm{}\left(\mathrm{th}\right)\mathrm{}}\approx 2.2\times {10}^{16}\mathrm{eV}\times {(B}_{\mathrm{cr}}/B)$ this contribution to the absorption of neutrinos yields an asymptotic absorption length $\approx 1.1\mathrm{m}\mathrm{}\times {(B}_{\mathrm{cr}}{/B)}^2\times {(10\mathrm{}}^{16}\mathrm{eV}/E).\mathrm{}$

The statics and dynamics of a surface separating two phases of a relativistic quantum field theory at or near the critical temperature typically make use of a free energy as a functional of an order parameter. This free energy functional also affords an economical description of states away from equilibrium. The similarities and differences between using a scalar field as the order parameter versus the energy density are examined, and a peculiarity is noted. We also point out several conceptual errors in the literature dealing with the dynamical prefactor in the nucleation rate.

Ori and Thorne have discussed the duration and observability (with LISA) of the transition from circular, equatorial inspiral to plunge for stellar-mass objects into supermassive ${(10\mathrm{}}^5-{10}^8{M}_{\odot })$ Kerr black holes. We extend their computation to eccentric Kerr equatorial orbits. Even with orbital parameters near exactly determined, we find that there is no universal length for the transition; rather, the length of the transition depends sensitively—essentially randomly—on initial conditions. Still, the Ori-Thorne zero-eccentricity results are essentially an upper bound on the length of eccentric transitions involving similar bodies (e.g., a fixed). Hence the implications for observations are no better: if the massive body is ${M=10\mathrm{}}^6{M}_{\odot },$ the captured body has a mass m, and the process occurs at distance d from LISA, then $S/N\lesssim {(m/10M}_{\odot }\left)\right(1\mathrm{}\mathrm{Gpc}/d)\times O(1),$ with the precise constant depending on the black hole spin. For low-mass bodies $(m\lesssim {7M}_{\odot })$ for which the event rate is at least vaguely understood, we expect little chance (probably [much] less than $10\%,$ depending strongly on the astrophysical assumptions) of LISA detecting a transition event with $S/N>\mathrm{}5\mathrm{}$ during its run; however, even a small infusion of higher-mass bodies or a slight improvement in LISA’s noise curve could potentially produce $S/N>\mathrm{}5\mathrm{}$ transition events during LISA’s lifetime.

For the quantized, massless, minimally coupled real scalar field in four-dimensional Minkowski space, we show (by an explicit construction) that weighted averages of the null-contracted stress-energy tensor along null geodesics are unbounded from below on the class of Hadamard states. Thus there are no quantum inequalities along null geodesics in four-dimensional Minkowski spacetime. This is in contrast with the case for two-dimensional flat spacetime, where such inequalities do exist. We discuss in detail the properties of the quantum states used in our analysis, and also show that the renormalized expectation value of the stress energy tensor evaluated in these states satisfies the averaged null energy condition (as expected), despite the nonexistence of a null-averaged quantum inequality. However, we also show that in any globally hyperbolic spacetime the null-contracted stress energy averaged over a timelike worldline does satisfy a quantum inequality bound (for both massive and massless fields). We comment briefly on the implications of our results for singularity theorems.

We present a new model for generalized parton distributions (GPDs), based on the aligned jet model, which successfully describes the deeply virtual Compton scattering (DVCS) data from H1, ZEUS, HERMES and CLAS. We also present an easily implementable and flexible algorithm for their construction. This new model is necessary since the most widely used models for GPDs, which are based on factorized double distributions, cannot, in their current form, describe the DVCS data when employed in a full QCD analysis. We demonstrate explicitly the reason for the shortcoming in the data description. We also highlight several nonperturbative input parameters which could be used to tune the GPDs, and the t dependence, to the DVCS data using a fitting procedure.

We show that the rigidly rotating quantum thermal distribution on flat space-time suffers from a global pathology which can be cured by introducing a cylindrical mirror if and only if it has a radius smaller than that of the speed-of-light cylinder. When this condition is met, we demonstrate numerically that the renormalized expectation value of the energy-momentum stress tensor corresponds to a rigidly rotating thermal bath up to a finite correction except on the mirror where there are the usual Casimir divergences.

We construct spherically and axially symmetric monopoles in SU(5) Yang-Mills-Higgs theory both in flat and curved space as well as spherical and axial non-Abelian, “hairy” black holes. We find that, in analogy with the SU(2) case, the flat space monopoles are either noninteracting (in the BPS limit) or repelling. In curved space, however, gravity is able to overcome the repulsion for suitable choices of the Higgs coupling constants and the gravitational coupling. In addition, we confirm that indeed all qualitative features of (gravitating) SU(2) monopoles are found as well in the SU(5) case. For the non-Abelian black holes, we compare the behavior of the solutions in the BPS limit with that for nonvanishing Higgs self-coupling constants.

The standard electroweak theory admits a string solution, the Z string, in which only the electrically neutral Higgs fields are excited. This solution is unstable at zero temperature: Z strings decay by exciting charged Higgs modes. In the early Universe, however, there was a long period during which the Higgs particles were out of equilibrium but the photon field was in thermal equilibrium. We show that in this phase Z strings are stabilized by interactions of the charged Higgs modes with the photons. In a first temperature range immediately below the electroweak symmetry breaking scale, the stabilized embedded defects are symmetric in internal space (the charged scalar fields are not excited). There is a second critical temperature below which the stabilized embedded strings undergo a core phase transition and the charged scalar fields take on a nonvanishing value in the core of the strings. We show that stabilized embedded defects with an asymmetric core persist to very low temperatures. The stabilization mechanism discussed in this paper is a prototypical example of a process which will apply to a wider class of embedded defects in gauge theories.

In the context of models where the dark energy density ${\rho }_D$ is a random variable, anthropic selection effects may explain both the “old” cosmological constant problem and the “time coincidence.” We argue that this type of solution to both cosmological constant problems entails a number of definite predictions, which can be checked against upcoming observations. In particular, the anthropic approach predicts that the dark energy equation of state is $p_D=-{\rho }_D$ with a very high accuracy, and that the dark energy density is greater than the currently favored value ${\Omega }_D\approx \mathrm{0.7.}$ Another prediction, which may be testable with an improved understanding of galactic properties, is that the conditions for civilizations to emerge arise mostly in galaxies completing their formation at low redshift, $z\approx 1.$ Finally, there is a prediction which is not likely to be tested observationally: our part of the universe is going to recollapse eventually, but it will take more than a trillion years of accelerated expansion before this happens.

We investigate observational constraints from present and future supernova data on a large class of decaying vacuum cosmologies. In such scenarios the present value of the vacuum energy density is quantified by a positive $\beta$ parameter smaller than unity. By assuming a Gaussian prior on the matter density parameter $({\Omega }_{\mathrm{m}}=0.35\mathrm{}\pm 0.07)$ we find ${\Omega }_{\mathrm{m}}{=0.34\mathrm{}}_{-0.12}^{+0.14\mathrm{}}$ and $\beta {=0.62\mathrm{}}_{-0.24}^{+0.12\mathrm{}}$ (95% C.L.) as the best fit values for the present data. We show that, while the current data cannot provide restrictive constraints on the ${\Omega }_{\mathrm{m}}-\beta$ plane, the future SNe data will limit considerably the allowed parameter space. A brief discussion about the equivalence between dynamical $\Lambda$ scenarios and scalar field cosmologies is also included.

In the two Higgs doublet model type III and in several other extensions of the standard model, there are no discrete symmetries that suppress flavor changing couplings at the tree level. The experimental observation of the ${\nu }_{\mu }–{\nu }_{\tau }$ flavor oscillation may suggest the non-conservation of the lepton number. This would lead to the decay of the type $A^0{/H}^0\to {\tau }^{\pm }{\mu }^{\mp }.$ We determine the present low energy limit on lepton flavor violating (LFV) couplings from the muon $g-2$ measurement and discuss the prospects for detecting lepton flavor violating decays at the Fermilab Tevatron and at the CERN Large Hadron Collider. The achievable bounds on the LFV coupling parameter ${\lambda }_{\tau \mu }$ are presented.

We investigate the quark sector of quenched QCD for $1.5<~{T/T}_c<~3$ in the continuum limit, using two different lattice discretizations of quarks and extrapolating from lattice spacings between $1/4T$ and $1/14T.$ At these temperatures, the flavor off-diagonal susceptibility ${\chi }_{\mathrm{ud}}{/T}^2$ is compatible with zero at each lattice spacing, and hence also in the continuum limit. In the continuum limit, the light quark susceptibilities are about 10% less than the ideal gas results even at the highest T, in agreement with hard thermal loop predictions but marginally below a resummed perturbative computation. For the mass range appropriate to the strange quark, the flavor diagonal susceptibility is significantly smaller. Our estimate of the Wroblewski parameter is compatible with observations at BNL RHIC and CERN SPS. The continuum limit of screening masses in all (local) quark bilinears is very close to the ideal gas results.

A new model for monopole catalysis of nucleon decay is proposed. Unlike in the earlier one, the only light fields in this model are the photon and Skyrme (pion) field. The model admits the ’t Hooft–Polyakov monopole and Skyrmion as classical solutions, while baryon number nonconservation occurs through an anomaly involving an intermediate mass axial vector field resembling W and Z bosons. By considering spherically symmetric monopole-Skyrmion configurations, we find that the Skyrmion loses essentially all its mass when interacting with the monopole, which is phenomenologically identical to the monopole catalysis of nucleon decay. Short-distance monopole-Skyrmion physics in this model is interesting too, as there exist almost degenerate metastable monopole-Skyrmion bound states separated by substantial energy barriers. Yet the height of the latter is much smaller than the physical nucleon mass, so the complete disappearance of the normal undeformed Skyrmion remains perfectly possible in Skyrmion-monopole scattering.

The spectrum of two-gluon glueballs below 3 GeV is investigated in a potential model with a dynamical gluon mass using the variational method. The short-distance potential is approximated by one-gluon exchange, while the long-distance part is taken as a breakable string. The mass and size of the radial as well as orbital excitations up to a principle quantum number $n=3\mathrm{}$ are evaluated. The predicted mass ratios are compared with experimental candidates and lattice results.

We analyze the form factors for the $\overrightarrow{B}\gamma l^{+}{l}^{-}$ weak transition. We show that making use of the gauge invariance of the $\overrightarrow{B}\gamma l^{+}{l}^{-}$ amplitude, the structure of the form factors in the resonance region, and their relations at large values of the photon energy results in efficient constraints on the behavior of the form factors. Based on these constraints, we propose a simple parametrization of the form factors and apply it to the lepton forward-backward (FB) asymmetry in the $\overrightarrow{B}\gamma l^{+}{l}^{-}$ decay. We find that the behavior of the FB asymmetry as a function of the photon energy, as well as the location of its zero, depend only weakly on the $\overrightarrow{B}\gamma$ form factors, and thus constitutes a powerful tool for testing the standard model.

We point out some intriguing analogies between field-theoretic solitons (topological defects) and D-branes. Annihilating soliton-antisoliton pairs can produce stable solitons of lower dimensionality. Solitons that localize massless gauge fields in their world-volume automatically imply the existence of open flux tubes ending on them and closed flux tubes propagating in the bulk. We discuss some aspects of this localization on explicit examples of unstable wall-antiwall systems. The annihilation of these walls can be described in terms of tachyon condensation which renders the world-volume gauge field nondynamical. During this condensation the world-volume gauge fields (open string states) are resonantly excited. These can later decay into closed strings, or get squeezed into a network of flux tubes similar to a network of cosmic strings formed at a cosmological phase transition. Although, as in the D-brane case, perturbatively one can find exact time-dependent solutions, when the energy of the system stays localized in the plane of the original soliton, such solutions are unstable with respect to decay into open and closed string states. Thus, when a pair of such walls annihilates, the energy is carried away (at least) by closed string excitations (“glueballs”), which are the lowest-energy excitations about the bulk vacuum. Suggested analogies can be useful for the understanding of the complicated D-brane dynamics and of the production of topological defects and reheating during brane collision in the early universe.

We propose a possible scheme for getting the known QCD scaling laws within string theory. In particular, we consider amplitudes for exclusive scattering of hadrons at large momentum transfer, hadronic form factors, and distribution functions.