Showing papers in "Physical Review D in 2001"

Essentials of k essence

Abstract: We recently introduced the concept of ``k-essence'' as a dynamical solution for explaining naturally why the universe has entered an epoch of accelerated expansion at a late stage of its evolution. The solution avoids fine-tuning of parameters and anthropic arguments. Instead, k-essence is based on the idea of a dynamical attractor solution which causes it to act as a cosmological constant only at the onset of matter domination. Consequently, k-essence overtakes the matter density and induces cosmic acceleration at about the present epoch. In this paper, we present the basic theory of k-essence and dynamical attractors based on evolving scalar fields with nonlinear kinetic energy terms in the action. We present guidelines for constructing concrete examples and show that there are two classes of solutions, one in which cosmic acceleration continues forever and one in which the acceleration has finite duration.

Ekpyrotic universe: Colliding branes and the origin of the hot big bang

Abstract: We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological horizon, flatness and monopole problems and generates a nearly scale-invariant spectrum of density perturbations without invoking superluminal expansion (inflation). The scenario relies, instead, on physical phenomena that arise naturally in theories based on extra dimensions and branes. As an example, we present our scenario predominantly within the context of heterotic M theory. A prediction that distinguishes this scenario from standard inflationary cosmology is a strongly blue gravitational wave spectrum, which has consequences for microwave background polarization experiments and gravitational wave detectors.

An Effective field theory for collinear and soft gluons: Heavy to light decays

Abstract: We construct the Lagrangian for an effective theory of highly energetic quarks with energy Q, interacting with collinear and soft gluons. This theory has two low energy scales, the transverse momentum of the collinear particles, ${p}_{\ensuremath{\perp}},$ and the scale ${p}_{\ensuremath{\perp}}^{2}/Q.$ The heavy to light currents are matched onto operators in the effective theory at one loop and the renormalization group equations for the corresponding Wilson coefficients are solved. This running is used to sum Sudakov logarithms in inclusive $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{s}\ensuremath{\gamma}$ and $\stackrel{\ensuremath{\rightarrow}}{B}{X}_{u}l\overline{\ensuremath{ u}}$ decays. We also show that the interactions with collinear gluons preserve the relations for the soft part of the form factors for heavy-to-light decays found by Charles et al. [Phys. Rev. D 60, 014001 (1999)], establishing these relations in the large energy limit of QCD.

Evidence for neutrino oscillations from the observation of $\bar{\nu}_e$ appearance in a $\bar{\nu}_\mu$ beam

Abstract: A search for ${\overline{\ensuremath{ u}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{ u}}}_{e}$ oscillations was conducted by the Liquid Scintillator Neutrino Detector at the Los Alamos Neutron Science Center using ${\overline{\ensuremath{ u}}}_{\ensuremath{\mu}}$ from ${\ensuremath{\mu}}^{+}$ decay at rest. A total excess of $87.9\ifmmode\pm\else\textpm\fi{}22.4\ifmmode\pm\else\textpm\fi{}6.0$ events consistent with ${\overline{\ensuremath{ u}}}_{e}\stackrel{\ensuremath{\rightarrow}}{p}{e}^{+}n$ scattering was observed above the expected background. This excess corresponds to an oscillation probability of $(0.264\ifmmode\pm\else\textpm\fi{}0.067\ifmmode\pm\else\textpm\fi{}0.045)%,$ which is consistent with an earlier analysis. In conjunction with other known limits on neutrino oscillations, the LSND data suggest that neutrino oscillations occur in the $0.2--10 {\mathrm{eV}}^{2}{/c}^{4} \ensuremath{\Delta}{m}^{2}$ range, indicating a neutrino mass greater than $0.4 \mathrm{eV}{/c}^{2}.$

Bounds on Universal Extra Dimensions

Abstract: We show that the bound from the electroweak data on the size of extra dimensions accessible to all the standard model elds is rather loose. These \universal" extra dimensions could have a compactication scale as low as 300 GeV for one extra dimension. This is because the Kaluza-Klein number is conserved and thus the contributions to the electroweak observables arise only from loops. The main constraint comes from weak-isospin violation eects. We also compute the contributions to the S parameter and the Zb b vertex. The direct bound on the compactication scale is set by CDF and D0 in the few hundred GeV range, and the Run II of the Tevatron will either discover extra dimensions or else it could signicantly raise the bound on the compactication scale. In the case of two universal extra dimensions, the current lower bound on the compactication scale depends logarithmically on the ultra-violet cuto of the higher dimensional theory, but can be estimated to lie between 400 and 800 GeV. With three or more extra dimensions, the cuto dependence may be too strong to allow an estimate.

Acoustic signatures in the primary microwave background bispectrum

Abstract: If the primordial fluctuations are non-Gaussian, then this non-Gaussianity will be apparent in the cosmic microwave background (CMB) sky. With their sensitive all-sky observation, MAP and Planck satellites should be able to detect weak non-Gaussianity in the CMB sky. On a large angular scale, there is a simple relationship between the CMB temperature and the primordial curvature perturbation: $\ensuremath{\Delta}T/T=\ensuremath{-}\ensuremath{\Phi}/3.$ On smaller scales, however, the radiation transfer function becomes more complex. In this paper, we present the angular bispectrum of the primary CMB anisotropy that uses the full transfer function. We find that the bispectrum has a series of acoustic peaks that change a sign and a period of acoustic oscillations is twice as long as that of the angular power spectrum. Using a single non-linear coupling parameter to characterize the amplitude of the bispectrum, we estimate the expected signal-to-noise ratio for COBE, MAP, and Planck experiments. In order to detect the primary CMB bispectrum by each experiment, we find that the coupling parameter should be larger than 600, 20, and 5 for COBE, MAP, and Planck experiments, respectively. Even for the ideal noise-free and infinitesimal thin-beam experiment, the parameter should be larger than 3. We have included effects from the cosmic variance, detector noise, and foreground sources in the signal-to-noise estimation. Since the simple inflationary scenarios predict that the parameter is an order of 0.01, the detection of the primary bispectrum by any kind of experiments should be problematic for those scenarios. We compare the sensitivity of the primary bispectrum to the primary skewness and conclude that, when we can compute the predicted form of the bispectrum, it becomes a ``matched filter'' for detecting the non-Gaussianity in the data and a much more powerful tool than the skewness. For example, we need the coupling parameter of larger than 800, 80, 70, and 60 for each relevant experiment in order to detect the primary skewness. We also show that MAP and Planck can separate the primary bispectrum from various secondary bispectra on the basis of the shape difference. The primary CMB bispectrum is a test of the inflationary scenario and also a probe of the non-linear physics in the very early universe.

Gravity with a dynamical preferred frame

Abstract: We study a generally covariant model in which local Lorentz invariance is broken by a dynamical unit timelike vector field ${u}^{a}$---the ``aether.'' Such a model makes it possible to study the gravitational and cosmological consequences of preferred frame effects, such as ``variable speed of light'' or high frequency dispersion, while preserving a generally covariant metric theory of gravity. In this paper we restrict attention to an action for an effective theory of the aether which involves only the antisymmetrized derivative ${\ensuremath{ abla}}_{[a}{u}_{b]}.$ Without matter this theory is equivalent to a sector of the Einstein-Maxwell-charged dust system. The aether has two massless transverse excitations, and the solutions of the model include all vacuum solutions of general relativity (as well as other solutions). However, the aether generally develops gradient singularities which signal a breakdown of this effective theory. Including the symmetrized derivative in the action for the aether field may cure this problem.

Inelastic dark matter

Abstract: Many observations suggest that much of the matter of the universe is nonbaryonic. Recently, the DAMA NaI dark matter direct detection experiment reported an annual modulation in their event rate consistent with a WIMP relic. However, the Cryogenic Dark Matter Search (CDMS) Ge experiment excludes most of the region preferred by DAMA. We demonstrate that if the dark matter can only scatter by making a transition to a slightly heavier state $(\ensuremath{\Delta}m\ensuremath{\sim}100 \mathrm{keV}),$ the experiments are no longer in conflict. Moreover, differences in the energy spectrum of nuclear recoil events could distinguish such a scenario from the standard WIMP scenario. Finally, we discuss the sneutrino as a candidate for inelastic dark matter in supersymmetric theories.

Trans-Planckian problem of inflationary cosmology

Abstract: In most current models of inflation based on a weakly self-coupled scalar matter field minimally coupled to gravity, the period of inflation lasts so long that, at the beginning of the inflationary period, the physical wavelengths of comoving scales which correspond to the present large-scale structure of the Universe were smaller than the Planck length. Thus, the usual computations of the spectrum of fluctuations in these models involve extrapolating low-energy physics (both in the matter and gravitational sector) into regions where this physics is not applicable. In this article we study the dependence of the usual predictions of inflation for the spectrum of cosmological fluctuations on the hidden assumptions about super-Planck scale physics. We introduce a class of modified dispersion relations to mimic possible effects of super-Planck scale physics, and find that, given an initial state determined by minimizing the energy density, for dispersions relations introduced by Unruh the spectrum is unchanged, whereas for a class of dispersion relations similar to those used by Corley and Jacobson (which involve a more radical departure from the usual linear relation) important deviations from the usual predictions of inflation can be obtained. Some implications of this result for the unification of fundamental physicsmore » and early Universe cosmology are discussed.« less

Softly broken A(4) symmetry for nearly degenerate neutrino masses

Abstract: The leptonic Higgs doublet model of neutrino masses is implemented with an ${A}_{4}$ discrete symmetry (the even permutation of four objects or equivalently the symmetry of the tetrahedron) which has four irreducible representations: $\underset{\ifmmode\bar\else\textasciimacron\fi{}}{1},{\underset{\ifmmode\bar\else\textasciimacron\fi{}}{1}}^{\ensuremath{'}},{\underset{\ifmmode\bar\else\textasciimacron\fi{}}{1}}^{\ensuremath{''}},$ and $\underset{\ifmmode\bar\else\textasciimacron\fi{}}{3}.$ The resulting spontaneous and soft breaking of ${A}_{4}$ provides a realistic model of charged-lepton masses as well as a nearly degenerate neutrino mass matrix. The phenomenological consequences at and below the TeV scale are discussed.

Optimized renormalization group flows

Abstract: We study the optimization of exact renormalization group (ERG) flows. We explain why the convergence of approximate solutions towards the physical theory is optimized by appropriate choices of the regularization. We consider specific optimized regulators for bosonic and fermionic fields and compare the optimized ERG flows with generic ones. This is done up to second order in the derivative expansion at both vanishing and nonvanishing temperature. We find that optimized flows at finite temperature factorize. This corresponds to the disentangling of thermal and quantum fluctuations. A similar factorization is found at second order in the derivative expansion. The corresponding optimized flow for a proper-time renormalization group is also provided to leading order in the derivative expansion. [DOI: 10.1103/PhysRevD.64.105007]

Largest temperature of the radiation era and its cosmological implications

Abstract: The thermal history of the universe before the epoch of nucleosynthesis is unknown. The maximum temperature in the radiation-dominated era, which we will refer to as the reheat temperature, may have been as low as 0.7 MeV. In this paper we show that a low reheat temperature has important implications for many topics in cosmology. We show that weakly interacting massive particles (WIMPs) may be produced even if the reheat temperature is much smaller than the freeze-out temperature of the WIMP, and that the dependence of the present abundance on the mass and the annihilation cross section of the WIMP differs drastically from familiar results. We revisit predictions of the relic abundance and resulting model constraints of supersymmetric dark matter, axions, massive neutrinos, and other dark matter candidates, nucleosynthesis constraints on decaying particles, and leptogenesis by decay of superheavy particles. We find that the allowed parameter space of supersymmetric models is altered, removing the usual bounds on the mass spectrum; the cosmological bound on massive neutrinos is drastically changed, ruling out Dirac (Majorana) neutrino masses $m_ u$ only in the range 33 keV $\simlt m_ u\simlt$ 6 (5) MeV, which is significantly smaller from the the standard disallowed range 94 eV $\simlt m_ u\simlt$ 2 GeV (this implies that massive neutrinos may still play the role of either warm or cold dark matter); the cosmological upper bound on the Peccei-Quinn scale may be significantly increased to $ 10^{16}$GeV from the usually cited limit of about $10^{12}$GeV; and that efficient out-of-equilibrium GUT baryogenesis and/or leptogenesis can take place even if the reheat temperature is much smaller than the mass of the decaying superheavy particle.

Regular magnetic black holes and monopoles from nonlinear electrodynamics

Abstract: It is shown that general relativity coupled to nonlinear electrodynamics (NED) with the Lagrangian $L(F),$ ${F=F}_{\ensuremath{\mu}\ensuremath{ u}}{F}^{\ensuremath{\mu}\ensuremath{ u}}$ having a correct weak field limit, leads to nontrivial spherically symmetric solutions with a globally regular metric if and only if the electric charge is zero and $L(F)$ tends to a finite limit as $\stackrel{\ensuremath{\rightarrow}}{F}\ensuremath{\infty}.$ The properties and examples of such solutions, which include magnetic black holes and solitonlike objects (monopoles), are discussed. Magnetic solutions are compared with their electric counterparts. A duality between solutions of different theories specified in two alternative formulations of NED (called the $\mathrm{FP}$ duality) is used as a tool for this comparison.

Conversion of conventional gravitational-wave interferometers into quantum nondemolition interferometers by modifying their input and/or output optics

Abstract: The LIGO-II gravitational-wave interferometers (ca. 2006–2008) are designed to have sensitivities near the standard quantum limit (SQL) in the vicinity of 100 Hz. This paper describes and analyzes possible designs for subsequent LIGO-III interferometers that can beat the SQL. These designs are identical to a conventional broad band interferometer (without signal recycling), except for new input and/or output optics. Three designs are analyzed: (i) a squeezed-input interferometer (conceived by Unruh based on earlier work of Caves) in which squeezed vacuum with frequency-dependent (FD) squeeze angle is injected into the interferometer’s dark port; (ii) a variational-output interferometer (conceived in a different form by Vyatchanin, Matsko and Zubova), in which homodyne detection with FD homodyne phase is performed on the output light; and (iii) a squeezed-variational interferometer with squeezed input and FD-homodyne output. It is shown that the FD squeezed-input light can be produced by sending ordinary squeezed light through two successive Fabry-Perot filter cavities before injection into the interferometer, and FD-homodyne detection can be achieved by sending the output light through two filter cavities before ordinary homodyne detection. With anticipated technology (power squeeze factor e-2R=0.1 for input squeezed vacuum and net fractional loss of signal power in arm cavities and output optical train e*=0.01) and using an input laser power Io in units of that required to reach the SQL (the planned LIGO-II power, ISQL), the three types of interferometer could beat the amplitude SQL at 100 Hz by the following amounts μ≡sqrt[Sh]/sqrt[ShSQL] and with the following corresponding increase V=1/μ3 in the volume of the universe that can be searched for a given noncosmological source: Squeezed input —μ≃sqrt[e-2R]≃0.3 and V≃1/0.33≃30 using Io/ISQL=1. Variational-output—μ≃e*1/4≃0.3 and V≃30 but only if the optics can handle a ten times larger power: Io/ISQL≃1/sqrt[e*]=10. Squeezed varational —μ=1.3(e-2Re*)1/4≃0.24 and V≃80 using Io/ISQL=1; and μ≃(e-2Re*)1/4≃0.18 and V≃180 using Io/ISQL=sqrt[e-2R/e*]≃3.2.

Flavor symmetry and the static potential with hypercubic blocking

Abstract: We introduce a new smearing transformation, the hypercubic (HYP) fat link. The hypercubic fat link mixes gauge links within hypercubes attached to the original link only. Using quenched lattices at $\ensuremath{\beta}=5.7$ and 6.0 we show that HYP fat links improve flavor symmetry by an order of magnitude relative to the thin link staggered action. The static potential measured on HYP smeared lattices agrees with the thin link potential at distances $r/ag~2$ and has greatly reduced statistical errors. These quenched results will be used in forthcoming dynamical simulations of HYP staggered fermions.

Gravity on a brane in infinite volume extra space

Abstract: We generalize the mechanism proposed in a previous paper and show that a four-dimensional relativistic tensor theory of gravitation can be obtained on a delta-function brane in flat infinite-volume extra space. In particular, we demonstrate that the induced Ricci scalar gives rise to Einstein's gravity on a delta-function type brane if the number of space-time dimensions is bigger than five. The bulk space exhibits the phenomenon of infrared transparency. That is to say, the bulk can be probed by gravitons with vanishing four-dimensional momentum square, while it is unaccessible to higher modes. This provides an attractive framework for solving the cosmological constant problem.

Sterile Neutrino Hot, Warm, and Cold Dark Matter

Abstract: We calculate the incoherent resonant and non-resonant scattering production of sterile neutrinos in the early universe. We find ranges of sterile neutrino masses, vacuum mixing angles, and initial lepton numbers which allow these species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM) candidates which meet observational constraints. The constraints considered here include energy loss in core collapse supernovae, energy density limits at big bang nucleosynthesis, and those stemming from sterile neutrino decay: limits from observed cosmic microwave background anisotropies, diffuse extragalactic background radiation, and ${}^{6}\mathrm{L}\mathrm{i}/\mathrm{D}$ overproduction. Our calculations explicitly include matter effects, both effective mixing angle suppression and enhancement (MSW resonance), as well as quantum damping. We for the first time properly include all finite temperature effects, dilution resulting from the annihilation or disappearance of relativistic degrees of freedom, and the scattering-rate-enhancing effects of particle-antiparticle pairs (muons, tauons, quarks) at high temperature in the early universe.

Gauge unification in higher dimensions

Abstract: A complete 5-dimensional $\mathrm{SU}(5)$ unified theory is constructed which, on compactification on the orbifold with two different ${Z}_{2}$'s ${(Z}_{2}$ and ${Z}_{2}^{\ensuremath{'}}),$ yields the minimal supersymmetric standard model. The orbifold accomplishes $\mathrm{SU}(5)$ gauge symmetry breaking, doublet-triplet splitting, and a vanishing of proton decay from operators of dimension 5. Until 4D supersymmetry is broken, all proton decay from dimension 4 and dimension 5 operators is forced to vanish by an exact ${U(1)}_{R}$ symmetry. Quarks and leptons and their Yukawa interactions are located at the ${Z}_{2}$ orbifold fixed points, where $\mathrm{SU}(5)$ is unbroken. A new mechanism for introducing $\mathrm{SU}(5)$ breaking into the quark and lepton masses is introduced, which originates from the $\mathrm{SU}(5)$ violation in the zero-mode structure of bulk multiplets. Even though $\mathrm{SU}(5)$ is absent at the ${Z}_{2}^{\ensuremath{'}}$ orbifold fixed point, the brane threshold corrections to gauge coupling unification are argued to be negligibly small, while the logarithmic corrections are small and in a direction which improves the agreement with the experimental measurements of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that $\stackrel{\ensuremath{\rightarrow}}{p}{e}^{+}{\ensuremath{\pi}}^{0}$ is expected with a rate within about one order of magnitude of the current limit. Supersymmetry breaking occurs on the ${Z}_{2}^{\ensuremath{'}}$ orbifold fixed point, and is felt directly by the gauge and Higgs sectors, while squarks and sleptons acquire mass via gaugino mediation, solving the supersymmetric flavor problem.

Penguin Enhancement and $B \to K\pi$ decays in perturbative QCD

Abstract: We compute the branching ratios of $\stackrel{\ensuremath{\rightarrow}}{B}K\ensuremath{\pi}$ decays in the framework of the perturbative QCD factorization theorem. Decay amplitudes are classified into the topologies of tree, penguin, and annihilation amplitudes, all of which contain both factorizable and nonfactorizable contributions. These contributions are expressed as the convolutions of hard $b$ quark decay amplitudes with universal meson wave functions. It is shown that (1) matrix elements of penguin operators are dynamically enhanced compared to those employed in the factorization assumption, (2) annihilation diagrams are not negligible, contrary to common belief, (3) annihilation diagrams contribute large strong phases, and (4) the uncertainty of the current data of the ratio $R=\mathrm{Br}{(B}_{d}^{0}\ensuremath{\rightarrow}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}})/\mathrm{Br}{(B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})$ and of $\mathrm{CP}$ asymmetries is too large to give a constraint of the unitarity angle ${\ensuremath{\varphi}}_{3}.$ Assuming ${\ensuremath{\varphi}}_{3}=90\ifmmode^\circ\else\textdegree\fi{}$ which is extracted from the best fit to the data of $R,$ predictions for the branching ratios of the four $\stackrel{\ensuremath{\rightarrow}}{B}K\ensuremath{\pi}$ modes are consistent with data.

Probing dark energy: methods and strategies

Abstract: The presence of dark energy in the Universe is inferred directly from the accelerated expansion of the Universe, and, indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Dark energy contributes about two-thirds of the critical density, is smoothly distributed, has large negative pressure, and is very mysterious. For now, all of its discernible cosmological consequences follow from its effect on the expansion rate of the Universe. Absent a compelling theoretical model (or even a class of models), we describe the dark energy by its equation of state ${w=p}_{X}/{\ensuremath{\rho}}_{X}$ which is allowed to vary with time. We describe and compare different approaches for determining $w(t),$ including a magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy. We focus particular attention on the use of a sample of several thousand type Ia supernova with redshifts $z\ensuremath{\lesssim}1.7,$ as might be gathered by the proposed SNAP satellite. Among other things, we derive optimal strategies for constraining cosmological parameters using type Ia supernovae. The redshift range $z\ensuremath{\simeq}0.2\ensuremath{-}2$ has the most leverage for probing ${w}_{X};$ supernovae and number counts appear to have the most potential to probe dark energy. Because the expansion rate depends upon both $w(t)$ and ${\ensuremath{\Omega}}_{M},$ an independent measurement of the matter density is critical for obtaining the most information about dark energy from cosmological observations.

Neutrino masses from large extra dimensions

Abstract: Recently it was proposed that the standard model (SM) degrees of freedom reside on a (3 + 1)-dimensional wall or ''3-brane'' embedded in a higher-dimensional spacetime. Furthermore, in this picture it is possible for the fundamental Planck mass M* to be as small as the weak scale M* approximate or equal to O(TeV) and the observed weakness of gravity at long distances is due the existence of new sub-millimeter spatial dimensions. We show that in this picture it is natural to expect neutrino masses to occur in the 10{sup {minus}1} - 10{sup {minus}4} eV range, despite the lack of any fundamental scale higher than M*. Such suppressed neutrino masses are not the result of a see-saw, but have intrinsically higher-dimensional explanations. We explore two possibilities. The first mechanism identifies any massless bulk fermions as right-handed neutrinos. These give naturally small Dirac masses for the same reason that gravity is weak at long distances in this framework. The second mechanism takes advantage of the large infrared desert: the space in the extra dimensions. Here, small Majorana neutrino masses are generated by breaking lepton number on distant branes.

Ultraviolet fixed point and generalized flow equation of quantum gravity

Abstract: A new exact renormalization group equation for the effective average action of Euclidean quantum gravity is constructed. It is formulated in terms of the component fields appearing in the transverse-traceless decomposition of the metric. It facilitates both the construction of an appropriate infrared cutoff and the projection of the renormalization group flow onto a large class of truncated parameter spaces. The Einstein-Hilbert truncation is investigated in detail and the fixed point structure of the resulting flow is analyzed. Both a Gaussian and a non-Gaussian fixed point are found. If the non-Gaussian fixed point is present in the exact theory, quantum Einstein gravity is likely to be renormalizable at the nonperturbative level. In order to assess the reliability of the truncation a comprehensive analysis of the scheme dependence of universal quantities is performed. We find strong evidence supporting the hypothesis that 4-dimensional Einstein gravity is asymptotically safe, i.e. nonperturbatively renormalizable. The renormalization group improvement of the graviton propagator suggests a kind of dimensional reduction from 4 to 2 dimensions when spacetime is probed at sub-Planckian length scales.

AdS/CFT and gravity

Abstract: The radiation-dominated k=0 FRW cosmology emerges as the induced metric on a codimension one hypersurface of constant extrinsic curvature in the five-dimensional AdS-Schwarzschild solution. That we should get FRW cosmology in this way is an expected result from AdS/CFT in light of recent comments regarding the coupling of gravity to ''boundary'' conformal field theories. I remark on how this calculation bears on the understanding of the Randall-Sundrum ''alternative to compactification.'' A generalization of the AdS/CFT prescription for computing Green's functions is suggested, and it is shown how gravity emerges from it with a strength G{sub 4}=2G{sub 5}/L. Some upper bounds are set on the radius of curvature L of AdS{sub 5}. One of them comes from estimating the rate of leakage of visible sector energy into the CFT. That rate is connected via a unitarity relation to deviations from Newton's force law at short distances. The best bound on L obtained in this paper comes from a match to the parameters of string theory. It is L{approx}<1nm if the string scale is 1GeV. Higher string scales imply a tighter bound on L.

Stability, causality, and Lorentz and CPT violation

Abstract: Stability and causality are investigated for quantum field theories incorporating Lorentz and $\mathrm{CPT}$ violation. Explicit calculations in the quadratic sector of a general renormalizable Lagrangian for a massive fermion reveal that no difficulty arises for low energies if the parameters controlling the breaking are small, but for high energies either energy positivity or microcausality is violated in some observer frame. However, this can be avoided if the Lagrangian is the sub-Planck limit of a nonlocal theory with spontaneous Lorentz and $\mathrm{CPT}$ violation. Our analysis supports the stability and causality of the Lorentz- and $\mathrm{CPT}$-violating standard-model extension that would emerge at low energies from spontaneous breaking in a realistic string theory.

Coalescence of two spinning black holes: An effective one-body approach

Abstract: We generalize to the case of spinning black holes a recently introduced ``effective one-body'' approach to the general relativistic dynamics of binary systems. We show how to approximately map the conservative part of the third post-Newtonian (3PN) dynamics of two spinning black holes of masses ${m}_{1},$ ${m}_{2}$ and spins ${\mathit{S}}_{1},$ ${\mathit{S}}_{2}$ onto the dynamics of a non-spinning particle of mass $\ensuremath{\mu}\ensuremath{\equiv}{m}_{1}{m}_{2}{/(m}_{1}{+m}_{2})$ in a certain effective metric ${g}_{\ensuremath{\mu}\ensuremath{ u}}^{\mathrm{eff}}{(x}^{\ensuremath{\lambda}};M,\ensuremath{ u},\mathit{a})$ which can be viewed either as a spin deformation [with the deformation parameter $\mathit{a}\ensuremath{\equiv}{\mathit{S}}_{\mathrm{eff}}/M]$ of the recently constructed 3PN effective metric ${g}_{\ensuremath{\mu}\ensuremath{ u}}^{\mathrm{eff}}{(x}^{\ensuremath{\lambda}};M,\ensuremath{ u}),$ or as a $\ensuremath{ u}$ deformation [with the comparable-mass deformation parameter $\ensuremath{ u}\ensuremath{\equiv}{m}_{1}{m}_{2}{/(m}_{1}{+m}_{2}{)}^{2}]$ of a Kerr metric of mass $M\ensuremath{\equiv}{m}_{1}{+m}_{2}$ and (effective) spin ${\mathit{S}}_{\mathrm{eff}}\ensuremath{\equiv}[{1+3m}_{2}{/(4m}_{1})]{\mathit{S}}_{1}+[{1+3m}_{1}{/(4m}_{2})]{\mathit{S}}_{2}.$ The combination of the effective one-body approach, and of a Pad\'e definition of the crucial effective radial functions, is shown to define a dynamics with much improved post-Newtonian convergence properties, even for black hole separations of the order of $6 {GM/c}^{2}.$ The complete (conservative) phase-space evolution equations of binary spinning black hole systems are written down and their exact and approximate first integrals are discussed. This leads to the approximate existence of a two-parameter family of ``spherical orbits'' (with constant radius), and of a corresponding one-parameter family of ``last stable spherical orbits'' (LSSO). These orbits are of special interest for forthcoming LIGO-VIRGO-GEO gravitational wave observations. The binding energy and total angular momentum of LSSO's are studied in some detail. It is argued that for most (but not all) of the parameter space of two spinning holes the approximate (leading-order) effective one-body approach introduced here gives a reliable analytical tool for describing the dynamics of the last orbits before coalescence. This tool predicts, in a quantitative way, how certain spin orientations increase the binding energy of the LSSO. This leads to a detection bias, in LIGO-VIRGO-GEO observations, favoring spinning black hole systems, and makes it urgent to complete the conservative effective one-body dynamics given here by adding (resummed) radiation reaction effects, and by constructing gravitational waveform templates that include spin effects. Finally, our approach predicts that the spin of the final hole formed by the coalescence of two arbitrarily spinning holes never approaches extremality.

Muon anomalous magnetic moment: A harbinger for ''new physics''

Abstract: Standard model loop contributions to the muon anomalous magnetic moment, a{sub {mu}}equivalent to(g{sub {mu}}-2)/2, and their theoretical uncertainties are scrutinized. The status and implications of the recently reported 2.6 sigma experiment versus theory deviation a{sub {mu}}{sup expt}-a{sub {mu}}{sup SM}=426(165) x 10{sup -11} are discussed. Possible explanations due to supersymmetric loop effects with m{sub SUSY}{approx_equal}55{sub -8}{sup +16}tan {beta} GeV, radiative mass mechanisms at the 1--2 TeV scale and other ''new physics'' scenarios are examined.

Radion dynamics and electroweak physics

Abstract: The dynamics of a stabilized radion in the Randall-Sundrum model with two branes is investigated, and the effects of the radion on electroweak precision observables are evaluated The radius is assumed to be stabilized using a bulk scalar field as suggested by Goldberger and Wise First the mass and the wave function of the radion is determined including the back reaction of the bulk stabilization field on the metric, giving a typical radion mass of the order of the weak scale This is demonstrated by a perturbative computation of the radion wave function A consequence of the background configuration for the scalar field is that after including the back reaction the Kaluza-Klein states of the bulk scalars couple directly to the standard model fields on the TeV brane Some cosmological implications are discussed, and in particular it is found that the shift in the radion at late times is in agreement with the four-dimensional effective theory result The effect of the radion on the oblique parameters is evaluated using an effective theory approach In the absence of a curvature-scalar Higgs mixing operator, these corrections are small and give a negative contribution to S In the presence of such a mixingmore » operator, however, the corrections can be sizable due to the modified Higgs and radion couplings« less

Scalar-tensor gravity in an accelerating universe

Abstract: We consider scalar-tensor theories of gravity in an accelerating universe. The equations for the background evolution and the perturbations are given in full generality for any parametrization of the Lagrangian, and we stress that apparent singularities are sometimes artifacts of a pathological choice of variables. Adopting a phenomenological viewpoint, i.e., from the observations back to the theory, we show that knowledge of the luminosity distance as a function of redshift up to $z\ensuremath{\sim}1\ensuremath{-}2,$ which is expected in the near future, severely constrains the viable subclasses of scalar-tensor theories. This is due to the requirement of positive energy for both the graviton and the scalar partner. Assuming a particular form for the Hubble diagram, consistent with present experimental data, we reconstruct the microscopic Lagrangian for various scalar-tensor models, and find that the most reasonable ones are obtained if the universe is (marginally) closed.

Gauge invariant effective Lagrangian for Kaluza-Klein modes

Abstract: We construct a manifestly gauge invariant Lagrangian in $3+1$ dimensions for N Kaluza-Klein modes of an $\mathrm{SU}(m)$ gauge theory in the bulk. For example, if the bulk is $4+1,$ the effective theory is ${\ensuremath{\Pi}}_{i=1}^{N+1}{\mathrm{SU}(m)}_{i}$ with N chiral $(\overline{m},m)$ fields connecting the groups sequentially. This can be viewed as a Wilson action for a transverse lattice in ${x}^{5},$ and is shown explicitly to match the continuum $4+1$ compactified Lagrangian truncated in momentum space. Scale dependence of the gauge couplings is described by the standard renormalization group technique with threshold matching, leading to effective power law running. We also discuss the unitarity constraints, and chiral fermions.

Neutrinos from propagation of ultrahigh energy protons

Abstract: We present a calculation of the production of neutrinos during propagation of ultrahigh energy cosmic rays, as may be produced in astrophysical sources. Photoproduction interactions are modeled with the event generator SOPHIA that represents very well the experimentally measured particle production cross sections at accelerator energies. We give the fluxes expected from different assumptions on cosmic ray source distributions, cosmic ray injection spectra, cosmological evolution of the sources and different cosmologies, and compare them to the Waxman-Bahcall limit on source neutrinos. We estimate rates for detection of neutrino induced showers in a ${\mathrm{km}}^{3}$ water detector. The ratio of the local high energy neutrino flux to the ultrahigh energy cosmic ray flux is a crucial parameter in distinguishing between astrophysical and cosmological (top-down) scenarios of the ultrahigh energy cosmic ray origin.