In this paper we derive a bound using data from cosmic rays physics on a model recently proposed to solve the hierarchy problem by lowering the Planck scale to the TeV region without the introduction of extra dimensions. We show that the nonobservation of small black holes by AGASA implies a model independent limit for the four-dimensional reduced Planck mass of roughly 488 GeV.

We analyze the constraints obtained from new atomic clock data on the possible time variation of the fine structure “constant” and the electron-proton mass ratio, and show how they are strengthened when the seasonal variation of the Sun’s gravitational field at the Earth’s surface is taken into account. We compare these bounds with those obtainable from tests of the weak equivalence principle and high redshift observations of quasar absorption spectra.

This paper continues the investigation of the modified Sakai-Sugimoto model proposed previously [J. High Energy Phys. 01 (2008) 055]. Here we discuss in detail numerical solutions to the classical equations for the brane profile and the tachyon condensate. An ultraviolet cutoff turns out to be essential because the numerical solutions tend to rapidly diverge from the desired asymptotic solutions, beyond a sufficiently large value of the holographic coordinate. The required cutoff is determined by the non-normalizable part of the tachyon and is parametrically far smaller than that dictated by consistency of a description in terms of ten-dimensional bulk gravity. We had argued [J. High Energy Phys. 01 (2008) 055] that the solution in which the tachyon field goes to infinity at the point where the brane and antibrane meet has only one free parameter, which may be taken to be the asymptotic brane-antibrane separation. Here we present numerical evidence in favor of this observation. We also present evidence that the non-normalizable part of the asymptotic tachyon solution, which is identified with quark mass in the QCD-like boundary theory, is determined by this parameter. We show that the normalizable part of the asymptotic tachyon solution determines the quark condensate, but this requires holographic renormalization of the on-shell boundary brane action because of the presence of infinite cutoff-dependent terms. Our renormalization scheme gives an exponential dependence on the cutoff to the quark mass. We also discuss meson spectra in detail and show that the pion mass is nonzero and satisfies the Gell-Mann-Oakes-Renner relation when a small quark mass is switched on.

We consider the phase transition of a string with tension ${\epsilon }_1$ to a string with a smaller tension ${\epsilon }_2$. The transition proceeds through quantum tunneling, and we calculate in arbitrary number of dimensions the preexponential factor multiplying the leading semiclassical exponential expression for the rate of the process. At ${\epsilon }_2=0$ the found formula for the decay rate also describes a breakup of a metastable string into two pieces.

In this paper, with an appropriate combination of three Liouville-type dilaton potentials, we obtain the higher dimensional charged slowly rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime. The angular momentum and the gyromagnetic ratio of such a black hole are determined for the arbitrary values of the dilaton coupling constant. It is shown that the dilaton field modifies the gyromagnetic ratio of the rotating dilaton black holes.

In loop quantum cosmology, the quantum dynamics is well understood. We approximate the full quantum dynamics in the infinite dimensional Hilbert space by projecting it on a finite dimensional submanifold thereof, spanned by suitably chosen semiclassical states. This submanifold is isomorphic with the classical phase space and the projected dynamical flow provides effective equations incorporating the leading quantum corrections to the classical equations of motion. Numerical work has been done using quantum states which are semiclassical at late times. These states follow the classical trajectory until the density is on the order of 1% of the Planck density then deviate strongly from the classical trajectory. The effective equations we obtain reproduce this behavior to surprising accuracy.

We discuss rotating wormholes in general relativity with a scalar field with negative kinetic energy. To solve the problem, we use the assumption about slow rotation. The role of a small dimensionless parameter plays the ratio of the linear velocity of rotation of the wormhole’s throat and the velocity of light. We construct the rotating wormhole solution in the second-order approximation with respect to the small parameter. The analysis shows that the asymptotical mass of the rotating wormhole is greater than that of the nonrotating one, and the null energy condition violation in the rotating wormhole spacetime is weaker than that in the nonrotating one.

We consider a loop-quantum gravity inspired modification of general relativity, where the Holst action is generalized by making the Barbero-Immirzi (BI) parameter a scalar field, whose value could be dynamically determined. The modified theory leads to a nonzero torsion tensor that corrects the field equations through quadratic first derivatives of the BI field. Such a correction is equivalent to general relativity in the presence of a scalar field with nontrivial kinetic energy. This stress energy of this field is automatically covariantly conserved by its own dynamical equations of motion, thus satisfying the strong equivalence principle. Every general relativistic solution remains a solution to the modified theory for any constant value of the BI field. For arbitrary time-varying BI fields, a study of cosmological solutions reduces the scalar-field stress energy to that of a pressureless perfect fluid in a comoving reference frame, forcing the scale-factor dynamics to be equivalent to those of a stiff equation of state. Upon ultraviolet completion, this model could provide a natural mechanism for $k$ inflation, where the role of the inflaton is played by the BI field and inflation is driven by its nontrivial kinetic energy instead of a potential.

A fully consistent linear perturbation theory for cosmology is derived in the presence of quantum corrections as they are suggested by properties of inverse volume operators in loop quantum gravity. The underlying constraints present a consistent deformation of the classical system, which shows that the discreteness in loop quantum gravity can be implemented in effective equations without spoiling space-time covariance. Nevertheless, nontrivial quantum corrections do arise in the constraint algebra. Since correction terms must appear in tightly controlled forms to avoid anomalies, detailed insights for the correct implementation of constraint operators can be gained. The procedures of this article thus provide a clear link between fundamental quantum gravity and phenomenology.

The transfer function $T(k)$ of dark matter (DM) perturbations during matter domination is obtained by solving the linearized collisionless Boltzmann-Vlasov equation. We provide an exact expression for $T(k)$ for arbitrary distribution functions of decoupled particles and initial conditions, which can be systematically expanded in a Fredholm series. An exhaustive numerical study of thermal relics for different initial conditions reveals that the first two terms in the expansion of $T(k)$ provide a remarkably accurate and simple approximation valid on all scales of cosmological relevance for structure formation in the linear regime. The natural scale of suppression is the free-streaming wave vector at matter-radiation equality, $k_{fs}(t_{\mathrm{eq}})=[4\pi {\rho }_{0M}/[⟨{\overrightarrow{V}}^2⟩(1+z_{\mathrm{eq}})]{]}^{1/2}$. An important ingredient is a nonlocal kernel determined by the distribution functions of the decoupled particles which describes the memory of the initial conditions and gravitational clustering and yields a correction to the fluid description. This correction is negligible at large scales $k\ll k_{fs}(t_{\mathrm{eq}})$ but it becomes important at small scales $k\ge k_{fs}(t_{\mathrm{eq}})$. Distribution functions that favor the small momentum region yield longer-range memory kernels and lead to an enhancement of power at small scales $k>k_{fs}(t_{\mathrm{eq}})$. Fermi-Dirac and Bose-Einstein statistics lead to long-range memory kernels, with longer-range for bosons, both resulting in enhancement of $T(k)$ at small scales. For DM thermal relics that decoupled while ultrarelativistic we find $k_{fs}(t_{\mathrm{eq}})\simeq 0.003(g_d/2{)}^{1/3}(m/\mathrm{keV})[\mathrm{kpc}{]}^{-1}$, where $g_d$ is the number of degrees of freedom at decoupling. For WIMPS we obtain $k_{fs}(t_{\mathrm{eq}})=5.88(g_d/2{)}^{1/3}(m/100\mathrm{GeV}{)}^{1/2}(T_d/10\mathrm{MeV}{)}^{1/2}[\mathrm{pc}{]}^{-1}$. For $k\ll k_{fs}(t_{\mathrm{eq}})$, $T(k)\sim 1-\mathrm{C}[k/k_{fs}(t_{\mathrm{eq}}){]}^2$ where $C=\mathrm{O}(1)$ and independent of statistics for thermal relics. We provide simple and accurate fits for $T(k)$ in a wide range of small scales $k>k_{fs}(t_{\mathrm{eq}})$ for thermal relics and different initial conditions. The numerical and analytic results for arbitrary distribution functions and initial conditions allow an assessment of DM candidates through their impact on structure formation.

The need to regularize loop integrals in a manner that preserves gauge invariance, for example, using the Pauli-Villars method, requires a subtraction that in the large mass limit hides its high momentum origin. This gives rise to the illusion that only nonrelativistic kaon loop momenta are relevant, when in fact this is not the case, as we show.

In this manuscript we comment on the criticism raised recently by Achasov and Kiselev [Phys. Rev. D 76, 077501 (2007)] on our work on the radiative decays $\varphi \to \gamma a_0/f_0$ [Eur. Phys. J. A 24, 437 (2005)]. Specifically, we demonstrate that their criticism relies on results that violate gauge invariance and is therefore invalid.

New experiments designed to discover a weakly interacting dark matter (DM) particle via spin dependent scattering can distinguish models of electroweak symmetry breaking. The plane of spin dependent versus spin-independent DM scattering cross sections is a powerful model diagnostic. We detail representative predictions of the minimal supergravity (mSUGRA) singlet extended standard model and minimal supersymmetric standard model, a new Dirac neutrino, littlest Higgs with $T$-parity (LHT), and minimal universal extra dimensions (mUED) models. Of these models, the nearly minimal supersymmetric standard model (nMSSM) has the largest spin dependent (SD) cross section. It has a very light neutralino which would give lower energy nuclear recoils. The focus point region of mSUGRA, mUED, and the right-handed neutrino also predict a very large SD cross section and predict a large signal of high energy neutrinos in the IceCube experiment from annihilations of dark matter in the Sun. We also describe a model-independent treatment of the scattering of DM particles of different intrinsic spins.

We show that the Loss-Yau zero modes of the 3d-Abelian-Dirac operator may be interpreted in a simple manner in terms of a stereographic projection from a 4d-Dirac operator with a constant field strength of definite helicity. This is an alternative to the conventional viewpoint involving Hopf maps from $S^3$ to $S^2$. Furthermore, our construction generalizes in a straightforward way to any odd dimension. The number of zero modes is related to the Chern-Simons number in a nonlinear manner.

We examine phantom dark energy models produced by a field with a negative kinetic term and a potential that satisfies the slow-roll conditions: $[(1/V)(dV/d\varphi ){]}^2\ll 1$ and $(1/V)(d^{2}V/d{\varphi }^2)\ll 1$. Such models provide a natural mechanism to produce an equation of state parameter, $w$, slightly less than $-1$ at present. Using techniques previously applied to quintessence, we show that in this limit, all such phantom models converge to a single expression for $w(a)$, which is a function only of the present-day values of ${\Omega }_{\varphi }$ and $w$. This expression is identical to the corresponding behavior of $w(a)$ for quintessence models in the same limit. At redshifts $z\lesssim 1$, this limiting behavior is well fit by the linear parametrization, $w=w_0+w_a(1-a)$, with $w_a\approx -1.5(1+w_0)$.

The spacetime physics of bulk closed string tachyon condensation is studied at the level of a two-derivative effective action. We derive the unique perturbative tachyon potential consistent with a full class of linearized tachyonic deformations of supercritical string theory. The solutions of interest deform a general linear dilaton background by the insertion of purely exponential tachyon vertex operators. In spacetime, the evolution of the tachyon drives an accelerated contraction of the universe and, absent higher-order corrections, the theory collapses to a cosmological singularity in finite time, at arbitrarily weak string coupling. When the tachyon exhibits a null symmetry, the worldsheet dynamics is known to be exact and well defined at tree level. We prove that if the two-derivative effective action is free of nongravitational singularities, higher-order corrections always resolve the spacetime curvature singularity of the null tachyon. The resulting theory provides an explicit mechanism by which tachyon condensation can generate or terminate the flow of cosmological time in string theory. Additional particular solutions can resolve an initial singularity with a tachyonic phase at weak coupling, or yield solitonic configurations that localize the universe along spatial directions.

Recent lattice data have reported an infrared suppressed, positivity violating gluon propagator which is nonvanishing at zero momentum and a ghost propagator which is no longer enhanced. This paper discusses how to obtain analytical results which are in qualitative agreement with these lattice data within the Gribov-Zwanziger framework. This framework allows one to take into account effects related to the existence of gauge copies, by restricting the domain of integration in the path integral to the Gribov region. We elaborate to great extent on a previous short paper by presenting additional results, also confirmed by the numerical simulations. A detailed discussion on the soft breaking of the Becchi-Rouet-Stora-Tyutin symmetry arising in the Gribov-Zwanziger approach is provided.

The thermodynamics of a scalar field with a quartic interaction is studied within the linear $\delta$ expansion (LDE) method. Using the imaginary-time formalism the free energy is evaluated up to second order in the LDE. The method generates nonperturbative results that are then used to obtain thermodynamic quantities like the pressure. The phase transition pattern of the model is fully studied, from the broken to the symmetry restored phase. The results are compared with those obtained with other nonperturbative methods and also with ordinary perturbation theory. The results coming from the two main optimization procedures used in conjunction with the LDE method, the principle of minimal sensitivity (PMS) and the fastest apparent convergence (FAC) are also compared with each other and studied in which cases they are applicable or not. The optimization procedures are applied directly to the free energy.

We study the transition from inspiral to plunge in general relativity by computing gravitational waveforms of nonspinning, equal-mass black-hole binaries. We consider three sequences of simulations, starting with a quasicircular inspiral completing 1.5, 2.3 and 9.6 orbits, respectively, prior to coalescence of the holes. For each sequence, the binding energy of the system is kept constant and the orbital angular momentum is progressively reduced, producing orbits of increasing eccentricity and eventually a head-on collision. We analyze in detail the radiation of energy and angular momentum in gravitational waves, the contribution of different multipolar components and the final spin of the remnant, comparing numerical predictions with the post-Newtonian approximation and with extrapolations of point-particle results. We find that the motion transitions from inspiral to plunge when the orbital angular momentum $L=L_{\mathrm{crit}}\simeq 0.8M^2$. For $L<L_{\mathrm{crit}}$ the radiated energy drops very rapidly. Orbits with $L\simeq L_{\mathrm{crit}}$ produce our largest dimensionless Kerr parameter for the remnant, $j=J/M^2\simeq 0.724\pm 0.13$ (to be compared with the Kerr parameter $j\simeq 0.69$ resulting from quasicircular inspirals). This value is in good agreement with the value of 0.72 reported in [I. Hinder, B. Vaishnav, F. Herrmann, D. Shoemaker, and P. Laguna, Phys. Rev. D 77, 081502 (2008).]. These conclusions are quite insensitive to the initial separation of the holes, and they can be understood by extrapolating point-particle results. Generalizing a model recently proposed by Buonanno, Kidder and Lehner [A. Buonanno, L. E. Kidder, and L. Lehner, Phys. Rev. D 77, 026004 (2008).] to eccentric binaries, we conjecture that (1) $j\simeq 0.724$ is close to the maximal Kerr parameter that can be obtained by any merger of nonspinning holes, and (2) no binary merger (even if the binary members are extremal Kerr black holes with spins aligned to the orbital angular momentum, and the inspiral is highly eccentric) can violate the cosmic censorship conjecture.

We investigate non-Gaussianity in the modulated reheating scenario where fluctuations of the decay rate of the inflaton generate adiabatic perturbations, paying particular attention to the nonlinearity (NL) parameters $f_{\mathrm{NL}}$, ${\tau }_{\mathrm{NL}}$, and $g_{\mathrm{NL}}$ as well as the scalar spectral index and tensor-to-scalar ratio which characterize the nature of the primordial power spectrum. We also take into account the preexisting adiabatic perturbations produced from the inflaton fluctuations. It has been known that the nonlinearity between the curvature perturbations and the fluctuations of the decay rate can yield non-Gaussianity at the level of $f_{\mathrm{NL}}\sim \mathcal{O}(1)$, but we find that the nonlinearity between the decay rate and the modulus field which determines the decay rate can generate much greater non-Gaussianity. We also discuss a consistency relation among nonlinearity parameters which holds in the scenario and find that the modulated reheating yields a different one from that of the curvaton model. In particular, they both can yield a large positive $f_{\mathrm{NL}}$ but with a different sign of $g_{\mathrm{NL}}$. This provides a possibility to discriminate these two competitive models by looking at the sign of $g_{\mathrm{NL}}$. Furthermore, we work on some concrete inflation models and investigate in what cases models predict the spectral index and the tensor-to-scalar ratio allowed by the current data while generating large non-Gaussianity, which may have many implications for model buildings of the inflationary universe.