The static and dynamic chiral susceptibilities in the quark-gluon plasma are calculated within lowest order perturbative QCD at finite temperature and the hard thermal loop resummation technique using an effective quark propagator. After regularization of ultraviolet divergences, the hard thermal loop results are compared to QCD lattice simulations.

We study instanton contributions to hadronic decays of the scalar glueball, the pseudoscalar charmonium state ${\eta }_c,$ and the scalar charmonium state ${\chi }_c.$ Hadronic decays of the ${\eta }_c$ are of particular interest. The three main decay channels are $K\overline{K}\pi ,\eta \pi \pi$ and ${\eta }^{\prime }\pi \pi ,$ each with an unusually large branching ratio $\sim 5\%.$ On the quark level, all three decays correspond to an instanton type vertex $\left(\overline{c}c\right)\left(\overline{s}s\right)\left(\overline{d}d\right)\left(ūu\right).\mathrm{}$ We show that the total decay rate into three pseudoscalar mesons can be reproduced using an instanton size distribution consistent with phenomenology and lattice results. Instantons correctly reproduce the ratio $B\left(\pi \pi \eta \right)/B\left(\pi \pi {\eta }^{\prime }\right)$ but overpredict the ratio $B\left(K\overline{K}\pi \right)/B\left[\pi \pi \eta \right({\eta }^{\prime }\left)\right].$ We consider the role of scalar resonances and suggest that the decay mechanism can be studied by measuring the angular distribution of decay products.

Using the information theory approach, in both its extensive and nonextensive versions, we estimate the inelasticity parameter K of hadronic reactions together with its distribution and energy dependence from $p\overline{p}$ and pp data. We find that the inelasticity remains essentially constant in energy except for a variation around $K\sim 0.5,$ as was originally expected.

In this paper we first study various model-independent bounds on lepton flavor violation in processes of $J/\psi ,$ ${\psi }^{\prime },$ and ${\rm Y}$ two-body decays, and then calculate their branching ratios in models of the leptoquark, the R violating minimally supersymmetric standard model, and top-color assisted technicolor models.

We study the model-building conditions under which a sizable $0\nu \beta \beta$-decay signal to the recently reported level of 0.4 eV is due to Kaluza-Klein singlet neutrinos in theories with large extra dimensions. Our analysis is based on 5-dimensional singlet-neutrino models compactified on an $S^1{/Z}_2$ orbifold, where the standard-model fields are localized on a 3-brane. We show that a successful interpretation of a positive signal within the above minimal 5-dimensional framework would require a non-vanishing shift of the 3-brane from the orbifold fixed points by an amount smaller than the typical scale $(100\mathrm{}\mathrm{MeV}{)}^{-1}$ characterizing the Fermi nuclear momentum. The resulting 5-dimensional models predict a sizable effective Majorana-neutrino mass that could be several orders of magnitude larger than the light neutrino masses. Most interestingly, the brane-shifted models with only one bulk sterile neutrino also predict novel trigonometric textures leading to mass scenarios with hierarchical active neutrinos and large ${\nu }_{\mu }-{\nu }_{\tau }$ and ${\nu }_e-{\nu }_{\mu }$ mixings that can fully explain the current atmospheric and solar neutrino data.

We study the duality of quasilocal energy and charges with nonorthogonal boundaries in the (2+1)-dimensional low-energy string theory. Quasilocal quantities shown in previous work and also some new variables arising from considering the nonorthogonal boundaries are presented, and the boost relations between these quantities are discussed. Moreover, we show that the dual properties of quasilocal variables, such as quasilocal energy density, momentum densities, surface stress densities, dilaton pressure densities, and Neveu-Schwarz charge density, are still valid in the moving observer’s frame.

We study the process of relaxation back to thermal equilibrium in $\mathrm{}(1+1)\mathrm{}$-dimensional conformal field theory at finite temperature. When the size of the system is much larger than the inverse temperature, perturbations decay exponentially with time. On the other hand, when the inverse temperature is large, the relaxation is oscillatory with the characteristic period set by the size of the system. We then analyze the intermediate regime in two specific models: namely, free fermions, and a strongly coupled large k conformal field theory which is dual to string theory on $\mathrm{}(2+1)\mathrm{}$-dimensional anti–de Sitter spacetime. In the latter case, there is a sharp transition between the two regimes in the $k=\infty$ limit, which is a manifestation of the gravitational Hawking-Page phase transition. In particular, we establish a direct connection between quasinormal and normal modes of the gravity system, and the decaying and oscillating behavior of the conformal field theory.

Black-hole (BH) binaries with single-BH masses $m=(5\mathrm{}\mathrm{-}{20)M}_{\odot },$ moving on quasicircular orbits, are among the most promising sources for first-generation ground-based gravitational-wave (GW) detectors. Until now, the development of data-analysis techniques to detect GWs from these sources has been focused mostly on nonspinning BHs. The data-analysis problem for the spinning case is complicated by the necessity to model the precession-induced modulations of the GW signal, and by the large number of parameters needed to characterize the system, including the initial directions of the spins, and the position and orientation of the binary with respect to the GW detector. In this paper we consider binaries of maximally spinning BHs, and we work in the adiabatic-inspiral regime to build families of modulated detection templates that (i) are functions of very few physical and phenomenological parameters, (ii) model remarkably well the dynamical and precessional effects on the GW signal, with fitting factors on average $\gtrsim 0.97,$ (iii) but, however, might require increasing the detection thresholds, offsetting at least partially the gains in the fitting factors. Our detection-template families are quite promising also for the case of neutron-star–black-hole binaries, with fitting factors on average $\approx \mathrm{0.93.}$ For these binaries we also suggest (but do not test) a further template family, which would produce essentially exact waveforms written directly in terms of the physical spin parameters.

Brane world models with “large” extra dimensions with radii in the $r_l\sim 10–100\mu \mathrm{m}$ range and smaller ones at $r_s<~(1\mathrm{}\mathrm{TeV}{)}^{-1}$ have the potential to solve the cosmic coincidence problem, i.e., the apparently fortuitous equality between dark matter and dark energy components today. The main ingredient is the assumption of a stabilization mechanism fixing the total volume of the compact submanifold, but allowing for shape deformations. The latter are associated with phenomenologically safe ultralight scalar fields. The bulk field Casimir energy naturally plays the role of dark energy, which decreases in time because of the expanding $r_l.$ Stable Kaluza-Klein states may play the role of dark matter with an increasing, ${O(1/r}_s),$ mass. The cosmological equations exhibit attractor solutions in which the global equation of state is negative, the ratio between dark energy and dark matter is constant, and the observed value of the ratio is obtained for two large extra dimensions. Experimental searches for large extra dimensions should take into account that, due to the strong coupling between dark matter and radii dynamics, the size of the large extra dimensions inside the galactic halo may be smaller than the average value.

In homogeneous universes the propagation of quantum fields gives rise to pair creation of quanta with opposite momenta. When computing expectation values of local operators, the correlations between these quanta are averaged out and no space-time structure is obtained. In this article, by an appropriate use of wave packets, we reveal the space-time structure of these correlations. We show that every pair emerges from vacuum configurations which are torn apart so as to give rise to two semiclassical currents: that carried by the particle and that of its “partner.” During inflation the partner’s current lives behind the Hubble horizon centered around the particle. Hence any measurement performed within a Hubble patch would correspond to an uncorrelated density matrix, as for Hawking radiation. However, when inflation stops, the Hubble radius grows and eventually encompasses the partner. When this is realized the coherence is recovered within a patch. In this paper, we focus on the case of a massive field with rare pair creation events. However, our analysis also applies to cases leading to arbitrary high occupation numbers. Hence it could be applied to primordial gravitational waves and primordial density fluctuations.

We reexamine the upper limits on the abundance of unstable massive relic particles provided by the success of big-bang nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, ${}^3$He, ${}^4$He, ${}^6$Li and ${}^7$Li. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of ${}^4$He and ${}^6$Li exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh $\sim 100\mathrm{GeV},$ their primordial abundance should have been below about ${10}^{-13}$ of the total entropy. This would imply an upper limit on the reheating temperature of a few times ${10}^7\mathrm{GeV},$ which could be a potential difficulty for some models of inflation. We discuss possible ways of evading this problem.

It has recently been proposed by Bastero-Gil, Mersini and co-workers that dark energy could be attributed to the cosmological properties of a scalar field with a nonstandard dispersion relation that decreases exponentially at wave numbers larger than the Planck scale ${(k}_{\mathrm{phys}}>M_{\mathrm{Pl}}).\mathrm{}$ In this scenario, the energy density stored in the modes of trans-Planckian wave numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present paper examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave numbers considered: hence, the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order $\sim M_{\mathrm{Pl}}^4)$ for modes with momenta $\sim M_{\mathrm{Pl}},$ far in excess of the background energy density. We evaluate the amount of fine tuning in the initial data necessary to avoid this back-reaction problem and find it is of order ${H/M}_{\mathrm{Pl}}.$ We also argue that the equation of state of the trans-Planckian modes is not vacuumlike. Therefore this model does not provide a suitable explanation for the dark energy.

Observational evidence suggests that our Universe is presently dominated by a dark energy component and is undergoing accelerated expansion. We recently introduced a model, motivated by string theory for short-distance physics, for explaining dark energy without appealing to any fine tuning. The idea of trans-Planckian dark energy (TDE) was based on the freeze-out mechanism of the ultralow frequency modes, $\omega \mathrm{}\left(k\right),$ of very short distances, by the expansion of the background universe, $\omega \mathrm{}\left(k\right)\mathrm{}<~H.\mathrm{}$ In this paper we address the issue of the stress-energy tensor for nonlinear short-distance physics and explain the need to modify Einstein equations in this regime. From the modified Einstein equations we then derive the equation of state for the TDE model, which has the distinctive feature of being continually time dependent. The explanation of the coincidence puzzle relies entirely on the intrinsic time evolution of the TDE equation of state.

Recent results from linear perturbation theory suggest that first-order cosmological quark-hadron phase transitions occurring as deflagrations may be “borderline” unstable, and those occurring as detonations may give rise to growing modes behind the interface boundary. However, since nonlinear effects can play important roles in the development of perturbations, unstable behavior cannot be asserted entirely by linear analysis, and the uncertainty of these recent studies is compounded further by nonlinearities in the hydrodynamics and self-interaction fields. In this paper we investigate the growth of perturbations and the stability of quark-hadron phase transitions in the early Universe by solving numerically the fully nonlinear relativistic hydrodynamics equations coupled to a scalar field with a quartic self-interaction potential regulating the transitions. We consider single, perturbed, phase transitions propagating either by detonation or deflagration, as well as multiple phase and shock front interactions in 1+2 dimensional spacetimes.

At least one state in the first family of D-wave $b\overline{b}$ quarkonium levels has been discovered near the predicted mass of $10.16\mathrm{GeV}{/c}^2.$ This state is probably the one with $J=2.\mathrm{}$ This state and the ones with $J=1\mathrm{}$ and $J=3\mathrm{}$ may contribute a detectable amount to the decay ${\rm Y}\mathrm{}\left(1D\right)\mathrm{}\to {\rm Y}\mathrm{}\left(1S\right)\mathrm{}\pi \pi ,$ depending on the partial widths for these decays for which predictions vary considerably. The prospects for detection of the chain ${\rm Y}\mathrm{}\left(3S\right)\mathrm{}\to {\rm Y}\mathrm{}\left(1D\right)+\overrightarrow{X}{\rm Y}\pi \pi +X$ are discussed.

The first order correction to the parton fragmentation functions in a thermal medium is derived in the leading logarithmic approximation in the framework of thermal field theory. The medium-modified evolution equations of the parton fragmentation functions are also derived. It is shown that all infrared divergences, both linear and logarithmic, in the real processes are canceled among themselves and by corresponding virtual corrections. The evolution of the quark number and the energy loss (or gain) induced by the thermal medium are investigated.

Electroweak radiative corrections can generate the neutrino $(\mathrm{mass}{)}^2$ difference required for the large mixing angle (LMA) solution to the solar neutrino problem if two of the neutrinos are assumed degenerate at high energy. We study this possibility and (i) derive restrictions on ranges of the high scale mixing matrix elements and (ii) obtain predictions for the low energy parameters required in order to get the LMA solution of the solar neutrino problem picked out by KamLAND. This solution is realized in the case of the standard model when the (degenerate) neutrino masses lie in the range $\left(0.7\mathrm{}-2\right)\mathrm{eV}.$ This is at odds with the cosmological limit $m_{\nu }<0.23\mathrm{}\mathrm{eV}$ (at $95\%\mathrm{C}.\mathrm{L}.\mathrm{})$ established recently using WMAP results. The LMA solution can be obtained in case of the MSSM electroweak corrections with a (almost) degenerate spectrum or with an inverted mass hierarchy for limited ranges in the high scale parameters.

We study the noncommutative version of the extended ADHM construction in eight dimensional $U\left(1\right)\mathrm{}$ Yang-Mills theory. This construction gives rise to the solutions of the BPS equations in Yang-Mills theory, and these solutions preserve at least 3/16 of supersymmetries. In a wide subspace of the extended ADHM data, we show that the integer k which appears in the extended ADHM construction should be interpreted as the $D4\mathrm{}$-brane charge rather than the $D0\mathrm{}$-brane charge by explicitly calculating the topological charges in the case that the noncommutativity parameter is anti-self-dual. We also find the relationship with the solution generating technique and show that the integer k can be interpreted as the charge of the $D0\mathrm{}$-brane bound to the $D8\mathrm{}$-brane with the B field in the case that the noncommutativity parameter is self-dual.

The interaction energy and force between widely separated strings is analyzed in a field theory having applications to superconducting cosmic strings, the SO(5) model of high-temperature superconductivity, and solitons in nonlinear optics. The field theory has two order parameters, one of which is broken in the vacuum (giving rise to strings), the other of which is unbroken in the vacuum but which could nonetheless be broken in the core of the string. If this does occur, there is an effect on the energetics of widely separated strings. This effect is important if the length scale of this second order parameter is longer than that of the other fields in the problem.

The action and the thermodynamics of a rotating black hole in the presence of a positive cosmological constant are analyzed. Since there is no spatial infinity, one must bring in, instead, a platform where the parameters characterizing the thermodynamic ensemble are specified. In the present treatment the platform in question is taken to be one of the two horizons, which is considered as a boundary. If the boundary is taken to be the cosmological horizon one deals with the action and thermodynamics of the black hole horizon. Conversely, if one takes the black hole horizon as the boundary, one deals with the action and thermodynamics of the cosmological horizon. The two systems are different. Their energy and angular momenta are equal in magnitude but have opposite sign. In either case, the energy and the angular momentum are obtained as surface terms on the boundary, according to the standard Hamiltonian procedure. The temperature and the rotational chemical potential are also expressed in terms of magnitudes on the boundary. If, in the resulting expressions, one continues the cosmological constant to negative values, the black hole thermodynamic parameters defined on the cosmological horizon coincide with those calculated at spatial infinity in the asymptotically anti–de Sitter case.