The problem of black hole production in trans-Planckian particle collisions is revisited, in the context of large extra dimensions scenarios of TeV-scale gravity. The validity of the standard description of this process (two colliding Aichelburg–Sexl shock waves in classical Einstein gravity) is questioned. It is observed that the classical spacetime has large curvature along the transverse collision plane, as signaled by the curvature invariant ${(R}_{\mu \nu \lambda \sigma }{)}^2.$ Thus quantum gravity effects, and in particular higher curvature corrections to the Einstein gravity, cannot be ignored. To give a specific example of what may happen, the collision is reanalyzed in the Einstein–Lanczos–Lovelock gravity theory, which modifies the Einstein–Hilbert Lagrangian by adding a particular “Gauss–Bonnet” combination of curvature squared terms. The analysis uses a series of approximations, which reduce the field equations to a tractable second order nonlinear PDE of the Monge–Ampère type. It is found that the resulting spacetime is significantly different from the pure Einstein case in the future of the transverse collision plane. These considerations cast serious doubts on the geometric cross section estimate, which is based on the classical Einstein gravity description of the black hole production process.

We propose a criterion for the validity of semiclassical gravity (SCG) which is based on the stability of the solutions of SCG with respect to quantum metric fluctuations. We pay special attention to the two-point quantum correlation functions for the metric perturbations, which contain both intrinsic and induced fluctuations. These fluctuations can be described by the Einstein-Langevin equation obtained in the framework of stochastic gravity. Specifically, the Einstein-Langevin equation yields stochastic correlation functions for the metric perturbations which agree, to leading order in the large N limit, with the quantum correlation functions of the theory of gravity interacting with N matter fields. The homogeneous solutions of the Einstein-Langevin equation are equivalent to the solutions of the perturbed semiclassical equation, which describe the evolution of the expectation value of the quantum metric perturbations. The information on the intrinsic fluctuations, which are connected to the initial fluctuations of the metric perturbations, can also be retrieved entirely from the homogeneous solutions. However, the induced metric fluctuations proportional to the noise kernel can only be obtained from the Einstein-Langevin equation (the inhomogeneous term). These equations exhibit runaway solutions with exponential instabilities. A detailed discussion about different methods to deal with these instabilities is given. We illustrate our criterion by showing explicitly that flat space is stable and a description based on SCG is a valid approximation in that case.

In an alternative mechanism recently proposed, adiabatic cosmological perturbations are generated at the decay of the inflaton field due to small fluctuations of its coupling to matter. This happens whenever the coupling is governed by the vacuum expectation value of another field, which acquires fluctuations during inflation. We discuss generalization and various possible implementations of this mechanism, and present some specific particle physics examples. In many cases the second field can start oscillating before perturbations are imprinted, or survive long enough so to dominate over the decay products of the inflaton. The primordial perturbations will then be modified accordingly in each case.

We study models in which the universe exits reheating at temperatures in the MeV regime. By combining light element abundance measurements with cosmic microwave background and large scale structure data we find a fairly robust lower limit on the reheating temperature of $T_{\mathrm{RH}}\gtrsim 4\mathrm{MeV}$ at 95% C.L. However, if the heavy particle whose decay reheats the universe has a direct decay mode to neutrinos, there are some small islands left in parameter space where a reheating temperature as low as 1 MeV is allowed. The derived lower bound on the reheating temperature also leads to very stringent bounds on models with n large extra dimensions. For $n=2\mathrm{}$ the bound on the compactification scale is $M\gtrsim 2000\mathrm{TeV},$ and for $n=3\mathrm{}$ it is 100 TeV. These are currently the strongest available bounds on such models.

Recently D. Vollick [Phys. Rev. D 68, 063510 (2003)] has shown that the inclusion of the $1/R$ curvature terms in the gravitational action and the use of the Palatini formalism offer an alternative explanation for cosmological acceleration. In this work we show not only that this model of Vollick does not have a good Newtonian limit, but also that any $f\left(R\right)\mathrm{}$ theory with a pole of order n in $R=0\mathrm{}$ and ${(d}^2{f/d}^2{R\left)\right(R}_0)\ne 0,$ where $R_0$ is the scalar curvature of background, does not have a good Newtonian limit.

The B modes generated by the lensing of cosmic microwave background (CMB) polarization are a primary target for the upcoming generation of experiments and can potentially constrain quantities such as the neutrino mass and dark energy equation of state. The net sample variance on the small scale B modes out to $l=2000\mathrm{}$ exceeds Gaussian expectations by a factor of 10 reflecting the variance of the larger scale lenses that generate them. It manifests itself as highly correlated band powers with correlation coefficients approaching 70% for wide bands of $\Delta l/l\sim \mathrm{0.25.}$ It will double the total variance for experiments that achieve a sensitivity of approximately $4\mu \mathrm{K}$ arcmin and a beam of several arcminutes or better. This non-Gaussianity must be taken into account in the analysis of experiments that go beyond first detection.

The topological approach to baryon-antibaryon production in the chiral phase transition is numerically simulated for rapidly expanding hadronic systems. For that purpose the dynamics of the effective chiral field is implemented on a space-rapidity lattice. The essential features of evolutions from initial “hot” configurations into final ensembles of (anti-)baryons embedded in the chiral condensate are studied in proper time of comoving frames. Typical times for onset and completion of the roll-down and exponents for the growth of correlations are extracted. Meson and baryon-antibaryon yields are estimated. For standard assumptions about initial coherence lengths they are compatible with experimental results.

We present an $E_6$ grand unified model with a realistic pattern of fermion masses. All standard model fermions are unified in three fundamental 27-plets (i.e., supersymmetry is not invoked), which involve in addition right-handed neutrinos and three families of vectorlike heavy quarks and leptons. The lightest of those can lie in the low-TeV range, being accessible to future collider experiments. As a result of the high symmetry, the masses and mixings of all fermions are closely related. The new heavy fermions play a crucial role for the quark and lepton mass matrices and the bilarge neutrino oscillations. In all channels generation mixing and $\mathcal{C}P$ violation arise from a single antisymmetric matrix. The $E_6$ breaking proceeds via an intermediate-energy region with ${\mathrm{SU}\left(3\right)\mathrm{}}_L\times {\mathrm{SU}\left(3\right)\mathrm{}}_R\times {\mathrm{SU}\left(3\right)\mathrm{}}_C$ gauge symmetry and a discrete left-right symmetry. This breaking pattern leads in a straightforward way to the unification of the three gauge coupling constants at high scales, providing for a long proton lifetime. The model also provides for the unification of the top, bottom, and tau Yukawa couplings and for new interesting relations in flavor and generation space.

We calculate the mean link in Landau gauge for Wilson and improved $\mathrm{SU}\left(3\right)\mathrm{}$ anisotropic gauge actions, using two loop perturbation theory and Monte Carlo simulation employing an accelerated Langevin algorithm. Twisted boundary conditions are employed, with a twist in all four lattice directions considerably improving the (Fourier accelerated) convergence to an improved lattice Landau gauge. Two loop perturbation theory is seen to predict the mean link extremely well even into the region of commonly simulated gauge couplings and so can be used to remove the need for numerical tuning of self-consistent tadpole improvement factors. A three loop perturbative coefficient is inferred from the simulations and is found to be small. We show that finite size effects are small and argue likewise for (lattice) Gribov copies and double Dirac sheets.

We discuss entropy bounds for two-dimensional gravity models. While the Bekenstein bound can be proved to hold in general for weakly gravitating matter, the analogous situation of the holographic bound is not universal, but depends on the specific model considered. We give a proof of the Bekenstein bound which is independent of the dimension of spacetime and of the gravity action.

We consider the entropy bounds recently conjectured by Fischler, Susskind, and Bousso, and proven in certain cases by Flanagan, Marolf, and Wald (FMW). One of the FMW derivations supposes a covariant form of the Bekenstein entropy bound, the consequences of which we explore. The derivation also suggests that the entropy contained in a vacuum spacetime, e.g., Schwarzschild spacetime, may be related to the shear on congruences of null rays. We find evidence for this intuition, but in a surprising way. We compare the covariant entropy bound to certain earlier discussions of black hole entropy, and comment on the separate roles of quantum mechanics and gravity in the entropy bound.

Cluster number counts can constrain the properties of dark energy if and only if the evolution in the relationship between observable quantities and the cluster mass can be calibrated. Next generation surveys with $\sim {10}^4$ clusters will have sufficient statistics to enable some degree of self-calibration. The excess variance of counts due to the clustering of clusters provides such an opportunity and can be measured from the survey without additional observational cost. It can minimize the degradation in dark energy constraints due to an unknown power-law evolution in the mass-observable relation improving constraints on the dark energy equation of state by a factor of 2 or more to $\sigma \mathrm{}\left(w\right)=0.06\mathrm{}$ for a deep $4000{\mathrm{deg}}^2$ survey.

Possible indirect detection of neutralino, through its $\gamma$-ray annihilation product, by the forthcoming GLAST satellite from our galactic halo, M31, M87, and the dwarf galaxies Draco and Sagittarius is studied. $\gamma$-ray fluxes are evaluated for two representative energy thresholds, 0.1 and 1.0 GeV, at which the spatial resolution of GLAST varies considerably. Apart from dwarfs, which are described either by a modified Plummer profile or by a tidally truncated King profile, fluxes are compared for halos with central cusps and cores. It is demonstrated that substructures, irrespective of their profiles, enhance the $\gamma$-ray emission only marginally. The expected $\gamma$-ray intensity above 1 GeV at high galactic latitudes is consistent with the residual emission derived from EGRET data if the density profile has a central core and $m_{\chi }<~50\mathrm{GeV},$ whereas for a central cusp only a substantial enhancement would explain the observations. From M31, the flux can be detected above 0.1 and 1.0 GeV by GLAST only if $m_{\chi }<~300\mathrm{GeV}$ and if the density profile has a central cusp, a case in which a significant boost in the $\gamma$-ray emission is produced by the central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the fluxes are always below the sensitivity limit of GLAST.

We consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles. We delineate the decay channels in which most of the decay energy ionizes and heats the intergalactic medium gas [and thus affects the cosmic microwave background (CMB)], and those in which most of the energy is carried away—e.g. photons with energies $100\mathrm{keV}\lesssim E\lesssim 1\mathrm{TeV}$—and thus appears as a contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to the decay-particle parameters from the CMB power spectrum thus complement those from the cosmic x-ray and γ-ray backgrounds. Although decaying particles can indeed produce an optical depth consistent with that reported by WMAP, in so doing they produce new fluctuations in the CMB temperature and polarization power spectra. For decay lifetimes less than the age of the Universe, the induced power spectra generally violate current constraints, while the power spectra are usually consistent if the lifetime is longer than the age of the Universe.

The count rate of weakly interacting massive particle (WIMP) dark matter candidates in direct detection experiments experiences an annual modulation due to the Earth’s motion around the Sun. In the standard isothermal halo model, the signal peaks near June 2nd at high recoil energies; however, the signal experiences a phase reversal and peaks in December at low energy recoils. We show that this phase reversal may be used to determine the WIMP mass. If an annual modulation were observed with the usual phase (i.e., peaking on June 2nd) in the lowest accessible energy recoil bins of the DAMA, CDMS-II, CRESST-II, EDELWEISS-II, GENIUS-TF, ZEPLIN-II, XENON, or ZEPLIN-IV detectors, one could immediately place upper bounds on the WIMP mass of 103, 48, 6, 97, 10, 52, 29, and 29 GeV, respectively. In addition, detectors with adequate energy resolution and sufficiently low recoil energy thresholds may determine the crossover recoil energy at which the phase reverses, thereby obtaining an independent measurement of the WIMP mass. We study the capabilities of various detectors, and find that CRESST-II, ZEPLIN-II, and GENIUS-TF should be able to observe the phase reversal in a few years of runtime, and can thus determine the mass of the WIMP if it is $O\left(100\mathrm{}\mathrm{GeV}\right).\mathrm{}$ Xenon based detectors with 1000 kg (XENON and ZEPLIN-IV) and with energy recoil thresholds of a few keV require 25 kg yr exposure, which will be readily attained in upcoming experiments.

We discuss a mixture of interacting neutral and charged Bose condensates, which is supposed being realized in the interior of neutron stars in the form of a coexistent neutron superfluid and protonic superconductor. We show that in this system, besides ordinary vortices of the $S^1\to S^1$ map, the neutron condensate also allows for (meta)stable finite-length knotted solitons, which are characterized by a nontrivial Hopf invariant and in some circumstances may be stabilized by a Faddeev-Skyrme term induced by the drag effect. We also consider a helical protonic flux tube in this system and show that, in contrast, it does not induce a Faddeev-Skyrme term.

By combining the recent WMAP measurements of the cosmic microwave background anisotropies and the results of the recent luminosity distance measurements to type-Ia supernovae, we find that the normalization of the matter power spectrum on cluster scales, ${\sigma }_8,$ can be used to discriminate between dynamical models of dark energy (quintessence models) and a conventional cosmological constant model $\left(\Lambda \mathrm{CDM}\right).\mathrm{}$

Anomaly mediation solves the supersymmetric flavor and CP problems. This is because the superconformal anomaly dictates that supersymmetry breaking is transmitted through nearly flavor-blind infrared physics that is highly predictive and UV insensitive. Slepton mass squareds, however, are predicted to be negative. This can be solved by adding D-terms for $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_Y$ and $\mathrm{U}{\mathrm{}\left(1\right)\mathrm{}}_{B-L}$ while retaining the UV insensitivity. In this paper we consider electroweak symmetry breaking via UV insensitive anomaly mediation in several models. For the minimal supersymmetric standard model we find a stable vacuum when $\tan \beta <1,$ but in this region the top Yukawa coupling blows up only slightly above the supersymmetry breaking scale. For the next-to-minimal supersymmetric standard model (NMSSM), we find a stable electroweak breaking vacuum but with a chargino that is too light. Replacing the cubic singlet term in the NMSSM superpotential with a term linear in the singlet we find a stable vacuum and viable spectrum. Most of the parameter region with correct vacua requires a large superpotential coupling, precisely what is expected in the “Fat Higgs” model in which the superpotential is generated dynamically. We have therefore found the first viable UV complete, UV insensitive supersymmetry breaking model that solves the flavor and CP problems automatically: the Fat Higgs model with UV insensitive anomaly mediation. Moreover, the cosmological gravitino problem is naturally solved, opening up the possibility of realistic thermal leptogenesis.

The high-energy behavior of string scattering in warped spacetimes is studied to all orders in perturbation theory. If one assumes that the theory is finite, the amplitudes exactly fall as powers of momentum.

We further investigate the procedure for computing tree-level amplitudes in Yang-Mills theory from connected instantons in the B model on $P^{3|4},$ emphasizing that the problem of calculating Feynman diagrams is recast into the problem of finding solutions to a certain set of algebraic equations. We show that the B model correctly reproduces all 6-particle amplitudes, including non-MHV amplitudes with three negative and three positive helicity gluons. As a further check, we also show that n-particle amplitudes obtained from the B model obey a number of properties required of gauge theory, such as parity symmetry (which relates an integral over degree d curves to one over degree $n-d-2$ curves) and the soft and collinear gluon poles.