In this paper we report on a major theoretical observation in cosmology. We present a concrete cosmological model for which inflation has a natural beginning and natural ending. Inflation is driven by a cosine-form potential, $V(\varphi )={\mathrm{\Lambda }}^4(1-\cos (\varphi /f))$, which begins at $\varphi \lesssim \pi f$ and ends at $\varphi ={\varphi }_{\text{end}}\lesssim 5f/3$. The distance traversed by the inflaton field $\varphi$ is sub-Planckian. The Gauss-Bonnet term ${\mathcal{R}}^2$ arising as leading curvature corrections in the action $S=\int d^{5}x\sqrt{-g_5}{M}^3(-6\lambda M^2+R+\alpha M^{-2}{\mathcal{R}}^2)+\int d^{4}x\sqrt{-g_4}({\dot{\varphi }}^2/2-V(\varphi )-\sigma +{\mathcal{L}}_{\text{matter}})$ (where $\alpha$ and $\lambda$ are constants and $M$ is the five-dimensional Planck mass) plays a key role to terminate inflation. The model generates appropriate tensor-to-scalar ratio $r$ and inflationary perturbations that are consistent with Planck and BICEP2 data. For example, for $N_{*}=50–60$ and $n_s\sim 0.960\pm 0.005$, the model predicts that $M\sim 5.64\times 10^{16}\mathrm{GeV}$ and $r\sim (0.14–0.21)$ [$N_{*}$ is the number of $e$-folds of inflation and $n_s$ ($n_t$) is the scalar (tensor) spectrum spectral index]. The ratio $-n_t/r$ is (13%–24%) less than its value in 4D Einstein gravity, $-n_t/r=1/8$. The upper bound on the energy scale of inflation $V^{1/4}=2.37\times 10^{16}\mathrm{GeV}$ ($r<0.27$) implies that $(-\lambda \alpha )\gtrsim 75\times 10^{-5}$ and $\mathrm{\Lambda }<2.17\times 10^{16}\mathrm{GeV}$, which thereby rule out the case $\alpha =0$ (Randall-Sundrum model). The true nature of gravity is holographic as implied by the braneworld realization of string and M theory. The model correctly predicts a late-epoch cosmic acceleration with the dark energy equation of state ${\mathrm{w}}_{\mathrm{D}E}\approx -1$.

Recently we derived a nonlinear U-spin amplitude relation for $D^0\to P^{+}{P}^{-}$, $P=\pi ,K$, predicted to hold up to fourth-order U-spin breaking terms of order $10^{-3}$. Here we study a similar relation for $D^0\to V^{+}{P}^{-},V=\rho ,K^{*}(892),P=\pi ,K$, expected to hold at an even higher accuracy of order $10^{-4}$. We confirm this prediction in spite of a large experimental error of about 20% in the amplitude of $D^0\to K^{*+}{\pi }^{-}$. We also comment briefly on U-spin breaking in $D^0\to P^{+}{V}^{-}$.

We study the three-flavor chirally and dilatation invariant extended linear sigma model with (pseudo)scalar and (axial-)vector mesons as well as a scalar dilaton field whose excitations are interpreted as a glueball. The model successfully describes masses and decay widths of quark-antiquark mesons in the low-energy region up to 1.6 GeV. Here we study in detail the vacuum properties of the scalar-isoscalar $J^{PC}=0^{++}$ channel and find that (i) a narrow glueball is only possible if the vacuum expectation value of the dilaton field is (at tree level) quite large (i.e. larger than what lattice QCD and QCD sum rules suggest) and (ii) only solutions in which $f_0(1710)$ is predominantly a glueball are found. Moreover, the resonance $f_0(1370)$ turns out to be mainly $(\overline{u}u+\overline{d}d)/\sqrt{2}$ and thus corresponds to the chiral partner of the pion, while the resonance $f_0(1500)$ is mainly $\overline{s}s$.

The shape of the electron is studied using lowest-order perturbation theory. Quantities used to probe the structure of the proton—form factors, generalized parton distributions, transverse densities, Wigner distributions and the angular momentum content—are computed for the electron-photon component of the electron wave function. The influence of longitudinally polarized photons, demanded by the need for infrared regularization via a nonzero photon mass, is included. The appropriate value of the photon mass depends on experimental conditions, and consequently the size of the electron (as defined by the slope of its Dirac form factor) bound in a hydrogen atom is found to be about four times larger than when the electron is in a continuum scattering state. The shape of the electron, as determined from the transverse density and generalized parton distributions, is shown not to be round, and the continuum electron is shown to be far less round than the bound electron. An electron distribution function (analogous to the quark distribution function) is defined, and that of the bound electron is shown to be suppressed compared to that of the continuum electron. If the relative transverse momentum of the virtual electron and photon is large compared with the electron mass, the virtual electron and photon each carry nearly the total angular momentum of the physical electron ($1/2$), with the orbital angular momentum being nearly ($-1/2$). Including the nonzero photon mass leads to the suppression of end-point contributions to form factors. Implications for proton structure and color transparency are discussed.

An analysis of $B^0\to D{K}^{*0}$ decays is presented, where $D$ represents an admixture of $D^0$ and ${\overline{D}}^0$ mesons reconstructed in four separate final states: $K^{-}{\pi }^{+}$, ${\pi }^{-}{K}^{+}$, $K^{+}{K}^{-}$ and ${\pi }^{+}{\pi }^{-}$. The data sample corresponds to $3.0{\mathrm{fb}}^{-1}$ of proton-proton collision, collected by the LHCb experiment. Measurements of several observables are performed, including $CP$ asymmetries. The most precise determination is presented of $r_B(D{K}^{*0})$, the magnitude of the ratio of the amplitudes of the decay $B^0\to D{K}^{+}{\pi }^{-}$ with a $b\to u$ or a $b\to c$ transition, in a $K\pi$ mass region of $\pm 50\mathrm{MeV}/c^2$ around the $K^{*}(892)$ mass and for an absolute value of the cosine of the $K^{*0}$ helicity angle larger than 0.4.

A Reply to the Comment by M. Novello, J. M. Salim, and Aline N. Araújo.

In a recent paper [Phys. Rev. D 85, 023528 (2012)] the authors proposed a generalized Born-Infeld electrodynamics coupled to general relativity which produces a nonsingular bouncing universe. For a magnetic universe the resulting cosmic evolution inevitably interpolates between asymptotic de Sitter states. Here we show that (i) the conclusion about the inevitability of the asymptotic vacuum regime in a magnetic universe is wrong, (ii) a sudden curvature singularity—not better than the big bang—arises, but for spaces of positive curvature, (iii) the square sound speed can be a negative quantity, signaling instability against small perturbations of the background energy density, and (iv) the speed of sound can exceed the speed of light, which raises a causality issue.

We analyze a spacetime structure on a new brane configuration constructed recently in the Dvali-Gabadadze-Porrati braneworld context. The brane, embedded on a five-dimensional bubble of nothing, has a wormhole structure. It is an exact solution without any matter fields, and thus the energy conditions for matter fields are trivially satisfied. We see that, under the traversability condition, the size of the bubble should be larger than ${10}^{10}\mathrm{cm}$ or so.

The thermal instanton determinant for the gauge group $SU(2)$ can be reduced to a form involving two simple functions. Various boundary conditions can be easily incorporated. Only a two dimensional integral has to be done numerically. As an example we compute the contribution to the free energy of $\mathcal{N}=1$ theory.

The traditional idea of the Pomeron/Reggeon description for hadron scattering is now being given theoretical foundation in gravity dual descriptions, where Pomeron corresponds to an exchange of spin-$j\in 2\mathbb{Z}$ states in the graviton trajectory. Deeply virtual Compton scattering (DVCS) is essentially a two-to-two scattering process of a hadron and a photon, and hence one should be able to study nonperturbative aspects (the generalized parton distribution [GPD]) of this process by the Pomeron/Reggeon process in gravity dual. We find, however, that even one of the most developed formulations of gravity dual, Pomeron [Brower-Polchinski-Strassler-Tan (BPST), 2006], is not able to capture skewness dependence of GPD properly. Therefore, we compute Reggeon wave functions on ${\mathrm{AdS}}_5$ so that the formalism of BPST can be generalized. These wave functions are used to determine the DVCS amplitude, bring it to the form of conformal operator product expansion/collinear factorization, and extract a holographic model of GPD, which naturally fits into the framework known as “dual parametrization,” or the “(conformal) collinear factorization approach.”

A perfect fluid, spatially flat cosmology in a $f(T)$ model, derived from a recently proposed general Born-Infeld-type theory of gravity is studied. Four-dimensional cosmological solutions are obtained assuming the equation of state $p=\omega \rho$. For a positive value of $\lambda$ (a parameter in the theory) the solution is singular (of the big bang type) but may have accelerated expansion at an early stage. For $\lambda <0$ there exists a nonzero minimum scale factor and a finite maximum value of the energy density, but the curvature scalar diverges. Interestingly, for $\lambda <0$, the Universe may undergo an eternal accelerated expansion with a de Sitter expansion phase at late times. We find these features without considering any extra matter field or even negative pressure. Fitting our model with supernova data we find that the simplest dust model ($p=0$), with $\lambda >0$, is able to generate acceleration and fits well, although the resulting properties of the Universe differ much from the known, present day, accepted values. The best fit model requires (with $\lambda >0$) an additional component of the physical matter density, with a negative value of the equation of state parameter, along with dust. The $\lambda <0$ solutions do not fit well with observations. Though these models do not explain the dark energy problem with consistency, their analysis does shed light on the plausibility of an alternative geometrical explanation.

We study the conditions imposed on matter to produce a regular (nonsingular) interior of a class of spherically symmetric black holes in the $f(T)$ extension of teleparallel gravity. The class of black holes studied (T spheres) is necessarily singular in general relativity. We derive a tetrad which is compatible with the black hole interior and utilize this tetrad in the gravitational equations of motion to study the black hole interior. It is shown that in the case where the gravitational Lagrangian is expandable in a power series $f(T)=T+\sum _{n\ne 1}{b}_n{T}^n$ black holes can be nonsingular while respecting certain energy conditions in the matter fields. Thus, the black hole singularity may be removed, and the gravitational equations of motion can remain valid throughout the manifold. This is true as long as $n$ is positive but is not true in the negative sector of the theory. Hence, gravitational $f(T)$ Lagrangians which are Taylor expandable in powers of $T$ may yield regular black holes of this type. Although it is found that these black holes can be rendered nonsingular in $f(T)$ theory, we conjecture that a mild singularity theorem holds in that the dominant energy condition is violated in an arbitrarily small neighborhood of the general relativity singular point if the corresponding $f(T)$ black hole is regular. The analytic techniques here can also be applied to gravitational Lagrangians which are not Laurent or Taylor expandable.

We study the effect of nonquadrupolar modes in the detection and parameter estimation of gravitational waves (GWs) from nonspinning black-hole binaries. We evaluate the loss of signal-to-noise ratio and the systematic errors in the estimated parameters when one uses a quadrupole-mode template family to detect GW signals with all the relevant modes, for target signals with total masses $20M_{\odot }\le M\le 250M_{\odot }$ and mass ratios $1\le q\le 18$. Target signals are constructed by matching numerical-relativity simulations describing the late inspiral, merger, and ringdown of the binary with post-Newtonian/effective-one-body waveforms describing the early inspiral. We find that waveform templates modeling only the quadrupolar modes of the GW signal are sufficient (loss of detection rate $<10\%$) for the detection of GWs with mass ratios $q\le 4$ using advanced GW observatories. Neglecting the effect of nonquadrupole modes will introduce systematic errors in the estimated parameters. The systematic errors are larger than the expected $1\sigma$ statistical errors for binaries with large, unequal masses ($q\gtrsim 4,M\gtrsim 150M_{\odot }$), for sky-averaged signal-to-noise ratios larger than 8. We provide a summary of the regions in the parameter space where neglecting nonquadrupole modes will cause unacceptable loss of detection rates and unacceptably large systematic biases in the estimated parameters.

Quantum graphity is a background independent model for emergent geometry, in which space is represented as a dynamical graph. The high-energy pregeometric starting point of the model is usually considered to be the complete graph; however, we also consider the empty graph as a candidate pregeometric state. The energetics as the graph evolves from either of these high-energy states to a low-energy geometric state is investigated as a function of the number of edges in the graph. Analytic results for the slope of this energy curve in the high-energy domain are derived, and the energy curve is determined exactly for small number of vertices $N$. To study the whole energy curve for larger (but still finite) $N$, an epitaxial approximation is introduced. This work may open the way to compare predictions from quantum graphity with observations of the early Universe, making the model falsifiable.

We investigate the negative modes about Coleman-De Luccia bounces governing vacuum transitions in de Sitter space, with the goal of gaining physical insight into the various anomalous results associated with these that have been reported in the literature. For the case of bounces with radii much less than the horizon distance $H^{-1}$ we find two distinct regimes, distinguished by the magnitude of the bubble nucleation rate $\mathrm{\Gamma }$. If $\mathrm{\Gamma }/H^4\gg 1$, then the behavior of the modes contributing to the determinant factors in $\mathrm{\Gamma }$ is much as it is in flat spacetime, and the calculation of $\mathrm{\Gamma }$ goes over smoothly to the flat spacetime calculation as the gravitational coupling is taken to zero. This is not the case if $\mathrm{\Gamma }/H^4\ll 1$. These two regimes correspond to the two possible outcomes of de Sitter vacuum decay—either a rapidly completed transition or nonpercolation and eternal inflation. For bounces with radii comparable to the horizon length, we confirm previous results concerning anomalous negative modes with support on the bounce wall. We also find further evidence supporting previous claims, based on thin-wall arguments, of the absence of expected negative modes for a class of bounces that arises when the initial and final vacua are nearly degenerate.

We propose a quantum experiment to measure with high precision the Schwarzschild spacetime parameters of the Earth. The scheme can also be applied to measure distances by taking into account the curvature of the Earth’s spacetime. As a wave packet of (entangled) light is sent from the Earth to a satellite it is redshifted and deformed due to the curvature of spacetime. Measurements after the propagation enable the estimation of the spacetime parameters. We compare our results with the state of the art, which involves classical measurement methods, and discuss what developments are required in space-based quantum experiments to improve on the current measurement of the Schwarzschild radius of the Earth.

Strong gravitational lensing forms multiple, time delayed images of cosmological sources, with the “focal length” of the lens serving as a cosmological distance probe. Robust estimation of the time delay distance can tightly constrain the Hubble constant as well as the matter density and dark energy. Current and next generation surveys will find hundreds to thousands of lensed systems but accurate time delay estimation from noisy, gappy light curves is potentially a limiting systematic. Using a large sample of blinded light curves from the Strong Lens Time Delay Challenge we develop and demonstrate a Gaussian process cross correlation technique that delivers an average bias within 0.1% depending on the sampling, necessary for subpercent Hubble constant determination. The fits are accurate (80% of them within one day) for delays from 5–100 days and robust against cadence variations shorter than six days. We study the effects of survey characteristics such as cadence, season, and campaign length, and derive requirements for time delay cosmology: in order not to bias the cosmology determination by $0.5\sigma$, the mean time delay fit accuracy must be better than 0.2%.

The apparent gamma-ray excess in the Galactic center region and inner Galaxy has attracted considerable interest, notably because both its spectrum and its radial distribution are consistent with an interpretation in terms of annihilating dark matter particles with a mass of about 10–40 GeV. We confront such an interpretation with an updated compilation of various indirect dark matter detection bounds, which we adapt to the specific form required by the observed signal. We find that cosmic-ray positron data strongly rule out dark matter annihilating to light leptons, or “democratically” to all leptons, as an explanation of the signal. Cosmic-ray antiprotons, for which we present independent and significantly improved limits with respect to previous estimates, are already in considerable tension with dark matter (DM) annihilation to any combination of quark final states; the first set of AMS-02 data will thus be able to rule out or confirm the DM hypothesis with high confidence. For reasonable assumptions about the magnetic field in the Galactic center region, radio observations independently put very severe constraints on a DM interpretation of the excess, in particular for all leptonic annihilation channels.

We classify effective actions for Nambu-Goldstone (NG) bosons assuming the absence of anomalies. Special attention is paid to Lagrangians that are invariant only up to a surface term, which are shown to be in a one-to-one correspondence with Chern-Simons (CS) theories for unbroken symmetry. Without making specific assumptions on the spacetime symmetry, we give explicit expressions for these Lagrangians, generalizing the Berry and Hopf terms in ferromagnets. Globally well-defined matrix expressions are derived for symmetric coset spaces of broken symmetry. The CS Lagrangians exhibit special properties, on both the perturbative and the global topological levels. The order-one CS term is responsible for the noninvariance of the canonical momentum density under internal symmetry, known as the linear momentum problem. The order-three CS term gives rise to a novel type of interaction among NG bosons. All the CS terms are robust against local variations of microscopic physics.

We explore the possibility of explaining a gamma-ray excess in the Galactic center, originally pointed out by Hooper, collaborators, and other groups, in an effective field theory framework. We assume that dark matter annihilation is mediated by particles heavy enough to be integrated out and that such particles couple to all quark families. We calculate the effective coupling required to explain the annihilation signal in the Galactic center and compare with bounds from direct detection, collider searches, and the requirement that the dark matter particles make up the appropriate fraction of the universal energy budget. We find that only a very small set of operators can explain the gamma-ray excess while being consistent with other constraints. Specifically, for scalar dark matter, the viable options are one scalar-type coupling to quarks and one interaction with gluons, while for fermionic (Dirac) dark matter, the viable options are two scalar-type dimension-7 operators or a dimension-6 vector-type operator. In all cases, future searches with the Large Hadron Collider should probe the relevant operators’ effective energy scale, while all viable interactions should escape direct detection experiments.