Showing papers in "Physical Review D in 2005"

Properties of singularities in the (phantom) dark energy universe

Abstract: The properties of future singularities are investigated in the universe dominated by dark energy including the phantom-type fluid. We classify the finite-time singularities into four classes and explicitly present the models which give rise to these singularities by assuming the form of the equation of state of dark energy. We show the existence of a stable fixed point with an equation of state $wl\ensuremath{-}1$ and numerically confirm that this is actually a late-time attractor in the phantom-dominated universe. We also construct a phantom dark energy scenario coupled to dark matter that reproduces singular behaviors of the Big Rip type for the energy density and the curvature of the universe. The effect of quantum corrections coming from conformal anomaly can be important when the curvature grows large, which typically moderates the finite-time singularities.

Constraints on the redshift dependence of the dark energy potential

Abstract: We develop a formalism to characterize the shape and the redshift evolution of the dark energy potential. Our formalism makes use of quantities similar to the horizon-flow parameters in inflation and is general enough that can deal with multiscalar quintessence scenarios, exotic matter components, and higher-order curvature corrections to General Relativity. We show how the shape of the dark energy potential can be recovered nonparametrically using this formalism and we present approximations analogous to the ones relevant to slow-roll inflation. Since presently available data do not allow a nonparametric and exact reconstruction of the potential, we consider a general parametric description. This reconstruction can also be used in other approaches followed in the literature (e.g., the reconstruction of the redshift evolution of the dark energy equation of state $w(z)$). Using observations of passively evolving galaxies and supernova data we derive constraints on the dark energy potential shape in the redshift range $0.1lzl1.8$. Our findings show that at the $1\ensuremath{\sigma}$ level the potential is consistent with being constant, although at the same level of confidence variations cannot be excluded with current data. We forecast constraints achievable with future data from the Atacama Cosmology Telescope.

Cosmological parameter analysis including SDSS Lyα forest and galaxy bias: Constraints on the primordial spectrum of fluctuations, neutrino mass, and dark energy

Abstract: We combine the constraints from the recent Ly$\ensuremath{\alpha}$ forest analysis of the Sloan Digital Sky Survey (SDSS) and the SDSS galaxy bias analysis with previous constraints from SDSS galaxy clustering, the latest supernovae, and 1st year WMAP cosmic microwave background anisotropies. We find significant improvements on all of the cosmological parameters compared to previous constraints, which highlights the importance of combining Ly$\ensuremath{\alpha}$ forest constraints with other probes. Combining WMAP and the Ly$\ensuremath{\alpha}$ forest we find for the primordial slope ${n}_{s}=0.98\ifmmode\pm\else\textpm\fi{}0.02$. We see no evidence of running, $dn/d\mathrm{ln} k=\ensuremath{-}0.003\ifmmode\pm\else\textpm\fi{}0.010$, a factor of $3$ improvement over previous constraints. We also find no evidence of tensors, $rl0.36$ ($95%$ c.l.). Inflationary models predict the absence of running and many among them satisfy these constraints, particularly negative curvature models such as those based on spontaneous symmetry breaking. A positive correlation between tensors and primordial slope disfavors chaotic inflation-type models with steep slopes: while the $V\ensuremath{\propto}{\ensuremath{\phi}}^{2}$ model is within the 2-sigma contour, $V\ensuremath{\propto}{\ensuremath{\phi}}^{4}$ is outside the 3-sigma contour. For the amplitude we find ${\ensuremath{\sigma}}_{8}=0.90\ifmmode\pm\else\textpm\fi{}0.03$ from the Ly$\ensuremath{\alpha}$ forest and WMAP alone. We find no evidence of neutrino mass: for the case of $3$ massive neutrino families with an inflationary prior, $\ensuremath{\sum}_{}^{}{m}_{\ensuremath{ u}}l0.42$ eV and the mass of lightest neutrino is ${m}_{1}l0.13$ eV at $95%$ c.l. For the 3 massless $+1$ massive neutrino case we find ${m}_{\ensuremath{ u}}l0.79$ eV for the massive neutrino, excluding at $95%$ c.l. all neutrino mass solutions compatible with the LSND results. We explore dark energy constraints in models with a fairly general time dependence of dark energy equation of state, finding ${\ensuremath{\Omega}}_{\ensuremath{\lambda}}=0.72\ifmmode\pm\else\textpm\fi{}0.02$, $\mathrm{w}(z=0.3)=\ensuremath{-}{0.98}_{\ensuremath{-}0.12}^{+0.10}$, the latter changing to $\mathrm{w}(z=0.3)=\ensuremath{-}{0.92}_{\ensuremath{-}0.10}^{+0.09}$ if tensors are allowed. We find no evidence for variation of the equation of state with redshift, $\mathrm{w}(z=1)=\ensuremath{-}{1.03}_{\ensuremath{-}0.28}^{+0.21}$. These results rely on the current understanding of the Ly$\ensuremath{\alpha}$ forest and other probes, which need to be explored further both observationally and theoretically, but extensive tests reveal no evidence of inconsistency among different data sets used here.

Iteration of planar amplitudes in maximally supersymmetric Yang-Mills theory at three loops and beyond

Abstract: We compute the leading-color (planar) three-loop four-point amplitude of N = 4 supersymmetric Yang-Mills theory in 4 - 2{epsilon} dimensions, as a Laurent expansion about {epsilon} = 0 including the finite terms. The amplitude was constructed previously via the unitarity method, in terms of two Feynman loop integrals, one of which has been evaluated already. Here we use the Mellin-Barnes integration technique to evaluate the Laurent expansion of the second integral. Strikingly, the amplitude is expressible, through the finite terms, in terms of the corresponding one- and two-loop amplitudes, which provides strong evidence for a previous conjecture that higher-loop planar N = 4 amplitudes have an iterative structure. The infrared singularities of the amplitude agree with the predictions of Sterman and Tejeda-Yeomans based on resummation. Based on the four-point result and the exponentiation of infrared singularities, we give an exponentiated ansatz for the maximally helicity-violating n-point amplitudes to all loop orders. The 1/{epsilon}{sup 2} pole in the four-point amplitude determines the soft, or cusp, anomalous dimension at three loops in N = 4 supersymmetric Yang-Mills theory. The result confirms a prediction by Kotikov, Lipatov, Onishchenko and Velizhanin, which utilizes the leading-twist anomalous dimensions in QCD computed by Moch, Vermaseren and Vogt. Following similar logic, we are able to predict a term in the three-loop quark and gluon form factors in QCD.

Quantum contributions to cosmological correlations

Abstract: The ``in-in'' formalism is reviewed and extended, and applied to the calculation of higher-order Gaussian and non-Gaussian correlations in cosmology. Previous calculations of these correlations amounted to the evaluation of tree graphs in the in-in formalism; here we also consider loop graphs. It turns out that for some though not all theories, the contributions of loop graphs as well as tree graphs depend only on the behavior of the inflaton potential near the time of horizon exit. A sample one-loop calculation is presented.

Constraining warm dark matter candidates including sterile neutrinos and light gravitinos with WMAP and the Lyman-{alpha} forest

Abstract: The matter power spectrum at comoving scales of $(1\ensuremath{-}40){h}^{\ensuremath{-}1}\text{ }\text{ }\mathrm{Mpc}$ is very sensitive to the presence of Warm Dark Matter (WDM) particles with large free-streaming lengths. We present constraints on the mass of WDM particles from a combined analysis of the matter power spectrum inferred from the large samples of high-resolution high signal-to-noise Lyman-$\ensuremath{\alpha}$ forest data of Kim et al. (2004) and Croft et al. (2002) and the cosmic microwave background data of WMAP. We obtain a lower limit of ${m}_{\mathrm{WDM}}\ensuremath{\gtrsim}550\text{ }\text{ }\mathrm{eV}$ ($2\ensuremath{\sigma}$) for early decoupled thermal relics and ${m}_{\mathrm{WDM}}\ensuremath{\gtrsim}2.0\text{ }\text{ }\mathrm{keV}$ ($2\ensuremath{\sigma}$) for sterile neutrinos. We also investigate the case where in addition to cold dark matter a light thermal gravitino with fixed effective temperature contributes significantly to the matter density. In that case the gravitino density is proportional to its mass, and we find an upper limit ${m}_{3/2}\ensuremath{\lesssim}16\text{ }\text{ }\mathrm{eV}$ ($2\ensuremath{\sigma}$). This translates into a bound on the scale of supersymmetry breaking, ${\ensuremath{\Lambda}}_{\mathrm{susy}}\ensuremath{\lesssim}260\text{ }\text{ }\mathrm{TeV}$, for models of supersymmetric gauge mediation in which the gravitino is the lightest supersymmetric particle.

Big-Bang nucleosynthesis and hadronic decay of long-lived massive particles

Abstract: We study the big-bang nucleosynthesis (BBN) with the long-lived exotic particle, called X. If the lifetime of X is longer than \sim 0.1 sec, its decay may cause non-thermal nuclear reactions during or after the BBN, altering the predictions of the standard BBN scenario. We pay particular attention to its hadronic decay modes and calculate the primordial abundances of the light elements. Using the result, we derive constraints on the primordial abundance of X. Compared to the previous studies, we have improved the following points in our analysis: The JETSET 7.4 Monte Carlo event generator is used to calculate the spectrum of hadrons produced by the decay of X; The evolution of the hadronic shower is studied taking account of the details of the energy-loss processes of the nuclei in the thermal bath; We have used the most recent observational constraints on the primordial abundances of the light elements; In order to estimate the uncertainties, we have performed the Monte Carlo simulation which includes the experimental errors of the cross sections and transfered energies. We will see that the non-thermal productions of D, He3, He4 and Li6 provide stringent upper bounds on the primordial abundance of late-decaying particle, in particular when the hadronic branching ratio of X is sizable. We apply our results to the gravitino problem, and obtain upper bound on the reheating temperature after inflation.

Inhomogeneous equation of state of the universe: Phantom era, future singularity and crossing the phantom barrier

Abstract: The dark energy universe equation of state (EOS) with inhomogeneous, Hubble parameter dependent term is considered. The motivation to introduce such a term comes from time-dependent viscosity considerations and modifications of general relativity. For several explicit examples of such EOS it is demonstrated how the type of future singularity changes, how the phantom epoch emerges and how the crossing of a phantom barrier occurs. Similar cosmological regimes are considered for the universe with two interacting fluids and for the universe with implicit EOS. For instance, the crossing of the phantom barrier is realized in an easier way, thanks to the presence of inhomogeneous term. The thermodynamical dark energy model is presented where the universe entropy may be positive even at the phantom era as a result of the crossing of the $w=\ensuremath{-}1$ barrier.

Quasinormal modes and holography

Abstract: Quasinormal frequencies of electromagnetic and gravitational perturbations in asymptotically anti-de Sitter spacetime can be identified with poles of the corresponding real-time Green's functions in a holographically dual finite temperature field theory. The quasinormal modes are defined for gauge-invariant quantities which obey an incoming-wave boundary condition at the horizon and a Dirichlet condition at the boundary. As an application, we explicitly find poles of retarded correlation functions of R-symmetry currents and the energy-momentum tensor in strongly coupled finite temperature N=4 supersymmetric SU(Nc) Yang-Mills theory in the limit of large Nc.

Cosmic growth history and expansion history

Abstract: The cosmic expansion history tests the dynamics of the global evolution of the universe and its energy density contents, while the cosmic growth history tests the evolution of the inhomogeneous part of the energy density. Precision comparison of the two histories can distinguish the nature of the physics responsible for the accelerating cosmic expansion: an additional smooth component---dark energy---or a modification of the gravitational field equations. With the aid of a new fitting formula for linear perturbation growth accurate to 0.05%--0.2%, we separate out the growth dependence on the expansion history and introduce a new growth index parameter $\ensuremath{\gamma}$ that quantifies the gravitational modification.

Gauss-Bonnet dark energy

Abstract: We propose the Gauss-Bonnet dark energy model inspired by string/M-theory where standard gravity with scalar contains additional scalar-dependent coupling with a Gauss-Bonnet invariant. It is demonstrated that the effective phantom (or quintessence) phase of the late universe may occur in the presence of such a term when the scalar is phantom or for nonzero potential (for canonical scalar). However, with the increase of the curvature, the Gauss-Bonnet term may become dominant so that the phantom phase is transient and the $w=\ensuremath{-}1$ barrier may be passed. Hence, the current acceleration of the universe may be caused by a mixture of scalar phantom and/or potential or stringy effects. It is remarkable that scalar-Gauss-Bonnet coupling acts against the big rip occurrence also in phantom cosmology.

Measurement of atmospheric neutrino oscillation parameters by Super-Kamiokande I

Abstract: We present a combined analysis of fully-contained, partially-contained and upward-going muon atmospheric neutrino data from a 1489 d exposure of the Super-Kamiokande detector. The data samples span roughly five decades in neutrino energy, from 100 MeV to 10 TeV. A detailed Monte Carlo comparison is described and presented. The data is fit to the Monte Carlo expectation, and is found to be consistent with neutrino oscillations of {nu}{sub {mu}}{r_reversible}{nu}{sub {tau}} with sin{sup 2}2{theta}>0.92 and 1.5x10{sup -3}<{delta}m{sup 2}<3.4x10{sup -3} eV{sup 2} at 90% confidence level.

Cosmology of generalized modified gravity models

Abstract: We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the Universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.

Diquark-antidiquark states with hidden or open charm and the nature of X(3872)

Abstract: Heavy-light diquarks can be the building blocks of a rich spectrum of states which can accommodate some of the newly observed charmoniumlike resonances not fitting a pure $c\overline{c}$ assignment. We examine this possibility for hidden and open charm diquark-antidiquark states deducing spectra from constituent quark masses and spin-spin interactions. Taking the $X(3872)$ as input we predict the existence of a ${2}^{++}$ state that can be associated to the $X(3940)$ observed by Belle and reexamine the state claimed by SELEX, $X(2632)$. The possible assignment of the previously discovered states ${D}_{s}(2317)$ and ${D}_{s}(2457)$ is discussed. We predict $X(3872)$ to be made of two components with a mass difference related to ${m}_{u}\ensuremath{-}{m}_{d}$ and discuss the production of $X(3872)$ and of its charged partner ${X}^{\ifmmode\pm\else\textpm\fi{}}$ in the weak decays of ${B}^{+,0}$.

Nonperturbative effect on dark matter annihilation and gamma ray signature from the galactic center

Abstract: Detection of gamma rays from dark matter annihilation in the galactic center is one of the feasible techniques to search for dark matter. We evaluate the gamma ray flux in the case that the dark matter has an electroweak SU(2)_L charge. Such dark matter is realized in the minimal supersymmetric standard model (MSSM) when the lightest SUSY particle is the Higgsino- or Wino-like neutralino. When the dark matter is heavy compared to the weak gauge bosons, the leading-order calculation of the annihilation cross sections in perturbation breaks down due to a threshold singularity. We take into account non-perturbative effects by using the non-relativistic effective theory for the two-body states of the dark matter and its SU(2)_L partner(s), and evaluate precise cross sections relevant to the gamma ray fluxes. We find that the annihilation cross sections may be enhanced by several orders of magnitude due to resonances when the dark matter mass is larger than 1 TeV. Furthermore, the annihilation cross sections in the MSSM may be changed by factors even when the mass is about 500 GeV. We also discuss sensitivities to gamma ray signals from the galactic center in the GLAST satellite detector and the large Air Cerenkov Telescope arrays.

Can dark energy evolve to the Phantom

Abstract: Dark energy with the equation of state $w(z)$ rapidly evolving from the dustlike ($w\ensuremath{\simeq}0$ at $z\ensuremath{\sim}1$) to the phantomlike ($\ensuremath{-}1.2\ensuremath{\lesssim}w\ensuremath{\lesssim}\ensuremath{-}1$ at $z\ensuremath{\simeq}0$) has been recently proposed as the best fit for the supernovae Ia data. Assuming that a dark energy component with an arbitrary scalar-field Lagrangian $p(\ensuremath{\varphi},{\ensuremath{ abla}}_{\ensuremath{\mu}}\ensuremath{\varphi})$ dominates in the flat Friedmann universe, we analyze the possibility of a dynamical transition from the states $(\ensuremath{\varphi},\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{\ensuremath{\varphi}})$ with $w\ensuremath{\ge}\ensuremath{-}1$ to those with $wl\ensuremath{-}1$ or vice versa. We have found that generally such transitions are physically implausible because they are either realized by a discrete set of trajectories in the phase space or are unstable with respect to the cosmological perturbations. This conclusion is confirmed by a comparison of the analytic results with numerical solutions obtained for simple models. Without the assumption of the dark energy domination, this result still holds for a certain class of dark energy Lagrangians, in particular, for Lagrangians quadratic in ${\ensuremath{ abla}}_{\ensuremath{\mu}}\ensuremath{\varphi}$. The result is insensitive to topology of the Friedmann universe as well.

New results on B→π,K,η decay form factors from light-cone sum rules

Abstract: We present an improved calculation of $B\ensuremath{\rightarrow}$ light pseudoscalar form factors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading-order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is 10 to 13% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters, in particular, those describing the twist-2 distribution amplitudes of the $\ensuremath{\pi}$, $K$, and $\ensuremath{\eta}$. We present our results in a way which details the dependence of the form factors on these parameters and facilitates the incorporation of future updates of their values from, e.g., lattice calculations.

Higher Charmonia

Abstract: This paper gives results for the spectrum, all allowed E1 radiative partial widths (and some important M1 widths) and all open-charm strong decay amplitudes of all 40 c-cbar states expected up to the mass of the 4S multiplet, just above 44 GeV The spectrum and radiative widths are evaluated using two models, the relativized Godfrey-Isgur model and a nonrelativistic potential model The electromagnetic transitions are evaluated using Coulomb plus linear plus smeared hyperfine wavefunctions, both in a nonrelativistic potential model and in the Godfrey-Isgur model The open-flavor strong decay amplitudes are determined assuming harmonic oscillator wavefunctions and the 3P0 decay model This work is intended to motivate future experimental studies of higher-mass charmonia, and may be useful for the analysis of high-statistics data sets to be accumulated by the BES, CLEO and GSI facilities

Reconciling dark energy models with f(R) theories

Abstract: Higher-order theories of gravity have recently attracted a lot of interest as alternative candidates to explain the observed cosmic acceleration without the need of introducing any scalar field. A critical ingredient is the choice of the function $f(R)$ of the Ricci scalar curvature entering the gravity Lagrangian and determining the dynamics of the Universe. We describe an efficient procedure to reconstruct $f(R)$ from the Hubble parameter $H$ depending on the redshift $z$. Using the metric formulation of $f(R)$ theories, we derive a third order linear differential equation for $f[R(z)]$ which can be numerically solved after setting the boundary conditions on the basis of physical considerations. Since $H(z)$ can be reconstructed from the astrophysical data, the method we present makes it possible to determine, in principle, what is the $f(R)$ theory which best reproduces the observed cosmological dynamics. Moreover, the method allows to reconcile dark energy models with $f(R)$ theories finding out what is the expression of $f(R)$ which leads to the same $H(z)$ of the given quintessence model. As interesting examples, we consider ``quiessence'' (dark energy with constant equation of state) and the Chaplygin gas.

Flavor Structure of Warped Extra Dimension Models

Abstract: We recently showed, in hep-ph/0406101, that warped extra dimensional models with bulk custodial symmetry and few TeV KK masses lead to striking signals at B-factories. In this paper, using a spurion analysis, we systematically study the flavor structure of models that belong to the above class. In particular we find that the profiles of the zero modes, which are similar in all these models, essentially control the underlying flavor structure. This implies that our results are robust and model independent in this class of models. We discuss in detail the origin of the signals in B-physics. We also briefly study other NP signatures that arise in rare K decays (K {yields} {pi}{nu}{nu}), in rare top decays [t {yields} c{gamma}(Z, gluon)] and the possibility of CP asymmetries in D{sup 0} decays to CP eigenstates such as K{sub s}{pi}{sup 0} and others. Finally we demonstrate that with light KK masses, {approx} 3 TeV, the above class of models with anarchic 5D Yukawas has a ''CP problem'' since contributions to the neutron electric dipole moment are roughly 20 times larger than the current experimental bound. Using AdS/CFT correspondence, these extra-dimensional models are dual to a purely 4D strongly coupled conformal Higgs sector thus enhancing their appeal.

Constraints on holographic dark energy from type Ia supernova observations

Abstract: In this paper, we use the type Ia supernovae data to constrain the holographic dark energy model proposed by Li. We also apply a cosmic age test to this analysis. We consider in this paper a spatially flat Friedmann-Robertson-Walker universe with a matter component and a holographic dark energy component. The fit result shows that the case $cl1$ ($c=0.21$) is favored, which implies that the holographic dark energy behaves as a quintom-type dark energy. Furthermore, we also perform a joint analysis of $\mathrm{SNe}+\mathrm{CMB}+\mathrm{LSS}$ to this model; the result is well improved and still upholds the quintom dark energy conclusion. The best fit results in our analysis are $c=0.81$, ${\ensuremath{\Omega}}_{m}^{0}=0.28$, and $h=0.65$, which lead to the present equation of state of dark energy ${w}_{0}=\ensuremath{-}1.03$ and the deceleration/acceleration transition redshift ${z}_{T}=0.63$. Finally, an expected supernova/acceleration probe simulation using $\ensuremath{\Lambda}\mathrm{CDM}$ as a fiducial model is performed on this model, and the result shows that the holographic dark energy model takes on $cl1$ ($c=0.92$) even though the dark energy is indeed a cosmological constant.

Beyond LISA: Exploring future gravitational wave missions

Abstract: The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer (BBO) have been proposed as follow on missions to the Laser Interferometer Space Antenna (LISA). Here we study the capabilities of these observatories, and how they relate to the science goals of the missions. We find that the Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension to the ALIA mission, will go considerably further toward meeting ALIA's main scientific goal of studying intermediate mass black holes. We also compare the capabilities of LISA to a related extension of the LISA mission, the Laser Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the initial deployment phase of the BBO would be sufficient to address the BBO's key scientific goal of detecting the Gravitational Wave Background, while still providing detailed information about foreground sources.

QCD factorization for semi-inclusive deep-inelastic scattering at low transverse momentum

Abstract: We argue a factorization formula for semi-inclusive deep-inelastic scattering with hadrons in the current fragmentation region detected at low transverse momentum. To facilitate the factorization, we introduce the transverse-momentum dependent parton distributions and fragmentation functions with gauge links slightly off the light cone, and with soft-gluon radiations subtracted. We verify the factorization to one-loop order in perturbative quantum chromodynamics and argue that it is valid to all orders in perturbation theory.

Phantom energy traversable wormholes

Abstract: It has been suggested that a possible candidate for the present accelerated expansion of the Universe is ``phantom energy''. The latter possesses an equation of state of the form $\ensuremath{\omega}\ensuremath{\equiv}p/\ensuremath{\rho}l\ensuremath{-}1$, consequently violating the null energy condition. As this is the fundamental ingredient to sustain traversable wormholes, this cosmic fluid presents us with a natural scenario for the existence of these exotic geometries. 'Note, however, that the notion of phantom energy is that of a homogeneously distributed fluid. Nevertheless, it can be extended to inhomogeneous spherically symmetric spacetimes, and it is shown that traversable wormholes may be supported by phantom energy. Because of the fact of the accelerating Universe, macroscopic wormholes could naturally be grown from the submicroscopic constructions that originally pervaded the quantum foam. One could also imagine an advanced civilization mining the cosmic fluid for phantom energy necessary to construct and sustain a traversable wormhole. In this context, we investigate the physical properties and characteristics of traversable wormholes constructed using the equation of state $p=\ensuremath{\omega}\ensuremath{\rho}$, with $\ensuremath{\omega}l\ensuremath{-}1$. We analyze specific wormhole geometries, considering asymptotically flat spacetimes and imposing an isotropic pressure. We also construct a thin shell around the interior wormhole solution, by imposing the phantom energy equation of state on the surface stresses. Using the ``volume integral quantifier'' we verify that it is theoretically possible to construct these geometries with vanishing amounts of averaged null energy condition violating phantom energy. Specific wormhole dimensions and the traversal velocity and time are also deduced from the traversability conditions for a particular wormhole geometry. These phantom energy traversable wormholes have far-reaching physical and cosmological implications. For instance, an advanced civilization may use these geometries to induce closed timelike curves, consequently violating causality.

Information loss in black holes

Abstract: The question of whether information is lost in black holes is investigated using Euclidean path integrals. The formation and evaporation of black holes is regarded as a scattering problem with all measurements being made at infinity. This seems to be well formulated only in asymptotically AdS spacetimes. The path integral over metrics with trivial topology is unitary and information preserving. On the other hand, the path integral over metrics with nontrivial topologies leads to correlation functions that decay to zero. Thus at late times only the unitary information preserving path integrals over trivial topologies will contribute. Elementary quantum gravity interactions do not lose information or quantum coherence.

B d , s → ρ , ω , K * , ϕ decay form factors from light-cone sum rules reexamined

Abstract: We present an improved calculation of $B\ensuremath{\rightarrow}$ light vector form factors from light-cone sum rules, including one-loop radiative corrections to twist-2 and twist-3 contributions, and leading order twist-4 corrections. The total theoretical uncertainty of our results at zero momentum transfer is typically 10% and can be improved, at least in part, by reducing the uncertainty of hadronic input parameters. We present our results in a way which details the dependence of the form factors on these parameters and facilitates the incorporation of future updates of their values from, e.g., lattice calculations. We also give simple and easy-to-implement parametrizations of the ${q}^{2}$ dependence of the form factors which are valid in the full kinematical regime of ${q}^{2}$.

Gravitational radiation from cosmic (super)strings: Bursts, stochastic background, and observational windows

Abstract: The gravitational wave (GW) signals emitted by a network of cosmic strings are reexamined in view of the possible formation of a network of cosmic superstrings at the end of brane inflation. The reconnection probability p of intersecting fundamental or Dirichlet strings might be much smaller than 1, and the properties of the resulting string network may differ significantly from those of ordinary strings (which have p=1). In addition, it has been recently suggested that the typical length of newly formed loops may differ by a factor {epsilon}<<1 from its standard estimate. Here, we analyze the effects of the two parameters p and {epsilon} on the GW signatures of strings. We consider both the GW bursts emitted from cusps of oscillating string loops, which have been suggested as candidate sources for the LIGO/VIRGO and LISA interferometers, and the stochastic GW background, which may be detectable by pulsar-timing observations. In both cases we find that previously obtained results are quite robust, at least when the loop sizes are not suppressed by many orders of magnitude relative to the standard scenario. We urge pulsar observers to reanalyze a recently obtained 17-yr combined data set to see whether the large scatter exhibited bymore » a fraction of the data might be due to a transient GW burst activity of some sort, e.g., to a near cusp event.« less

Dark energy: Vacuum fluctuations, the effective phantom phase, and holography

Abstract: We aim at the construction of dark energy models without exotic matter but with a phantomlike equation of state (an effective phantom phase) The first model we consider is decaying vacuum cosmology where the fluctuations of the vacuum are taken into account In this case, the phantom cosmology (with an effective, observational $\ensuremath{\omega}$ being less than $\ensuremath{-}1$ ) emerges even for the case of a real dark energy with a physical equation of state parameter $\ensuremath{\omega}$ larger than $\ensuremath{-}1$ The second proposal is a generalized holographic model, which is produced by the presence of an infrared cutoff It also leads to an effective phantom phase, which is not a transient one as in the first model However, we show that quantum effects are able to prevent its evolution towards a big rip singularity

Reconstructing the universe

Abstract: We provide detailed evidence for the claim that nonperturbative quantum gravity, defined through state sums of causal triangulated geometries, possesses a large-scale limit in which the dimension of spacetime is four and the dynamics of the volume of the universe behaves semiclassically. This is a first step in reconstructing the universe from a dynamical principle at the Planck scale, and at the same time provides a nontrivial consistency check of the method of causal dynamical triangulations. A closer look at the quantum geometry reveals a number of highly nonclassical aspects, including a dynamical reduction of spacetime to two dimensions on short scales and a fractal structure of slices of constant time.

Electroweak-scale resonant leptogenesis

Abstract: We study minimal scenarios of resonant leptogenesis near the electroweak phase transition. These models offer a number of testable phenomenological signatures for low-energy experiments and future high-energy colliders. Our study extends previous analyses of the relevant network of Boltzmann equations, consistently taking into account effects from out of equilibrium sphalerons and single lepton flavors. We show that the effects from single lepton flavors become very important in variants of resonant leptogenesis, where the observed baryon asymmetry in the Universe is created by lepton-to-baryon conversion of an individual lepton number, for example, that of the {tau}-lepton. The predictions of such resonant {tau}-leptogenesis models for the final baryon asymmetry are almost independent of the initial lepton-number and heavy neutrino abundances. These models accommodate the current neutrino data and have a number of testable phenomenological implications. They contain electroweak-scale heavy Majorana neutrinos with appreciable couplings to electrons and muons, which can be probed at future e{sup +}e{sup -} and {mu}{sup +}{mu}{sup -} high-energy colliders. In particular, resonant {tau}-leptogenesis models predict sizable 0{nu}{beta}{beta} decay, as well as e- and {mu}-number-violating processes, such as {mu}{yields}e{gamma} and {mu}{yields}e conversion in nuclei, with rates that are within reach of the experiments proposed by the MEG and MECOmore » collaborations.« less