We investigate the course of cosmic expansion in its recent past using the Constitution SN Ia sample, along with baryon acoustic oscillations (BAO) and cosmic microwave background (CMB) data. Allowing the equation of state of dark energy (DE) to vary, we find that a coasting model of the universe ($q_0=0$) fits the data about as well as Lambda cold dark matter. This effect, which is most clearly seen using the recently introduced $Om$ diagnostic, corresponds to an increase of $Om$ and $q$ at redshifts $z\lesssim 0.3$. This suggests that cosmic acceleration may have already peaked and that we are currently witnessing its slowing down. The case for evolving DE strengthens if a subsample of the Constitution set consisting of $\mathrm{SNLS}+\mathrm{\text{ESSENCE}}+\mathrm{CfA}\mathrm{SN}\mathrm{Ia}$ data is analyzed in combination with $\mathrm{BAO}+\mathrm{CMB}$ data. The effect we observe could correspond to DE decaying into dark matter (or something else).

We study the potential LHC discovery of the $Z_1$ Kaluza-Klein gauge boson unitarizing $W_L^{+}{W}_L^{-}$ scattering amplitude. In particular, we explore the decay mode $Z_1\to t\overline{t}$, along with $Z_1\to W^{+}{W}^{-}$, without specifying the branching fractions. We propose to exploit the associated production $pp\to W{Z}_1$ and select the final state of like-sign dileptons plus multijets and large missing energy. We conclude that it is possible to observe the $Z_1$ resonance at a $5\sigma$ level with an integrated luminosity of $100{\mathrm{fb}}^{-1}$ at the LHC up to 650 GeV for a dominant $WW$ channel, and 560 GeV for a dominant $t\overline{t}$ channel.

Considering the present limits on their masses from the Tevatron experiments, the fourth-family quarks are expected to have masses larger than the top quark. Because of their expected large masses, they could have different dynamics than the third-family quarks of the standard model. The resonant production of the fourth-family up-type quark $t^{\prime }$ has been studied via the anomalous production subprocess $g{q}_i\to t^{\prime }$ (where $q_i=u$, $c$) at the LHC, with center-of-mass energies of 10 TeV and 14 TeV. The signatures of such a process are discussed within the standard model decay modes. The sensitivity to the anomalous coupling $\kappa /\Lambda =0.1{\mathrm{TeV}}^{-1}$ can be reached at $\sqrt{s}=10\mathrm{TeV}$ and $L_{\mathrm{int}}=100{\mathrm{pb}}^{-1}$.

We propose a minimal extension of the standard model in which neutrinos are Dirac particles and their tiny masses are explained without requiring tiny Yukawa couplings. A second Higgs doublet with a tiny vacuum expectation value provides neutrino masses while simultaneously improving the naturalness of the model by allowing a heavier standard-model-like Higgs boson consistent with electroweak precision data. The model predicts a $\mu \to e\gamma$ rate potentially detectable in the current round of experiments, as well as distinctive signatures in the production and decay of the charged Higgs $H^{+}$ of the second doublet which can be tested at future colliders. Neutrinoless double beta decay is absent.

We present numerical results for the phase diagram of lattice QCD at finite temperature in the formulation with twisted mass Wilson fermions and a tree-level Symanzik-improved gauge action. Our simulations are performed on lattices with temporal extent $N_{\tau }=8$, and lattice coupling $\beta$ ranging from strong coupling to the scaling domain. Covering a wide range in the space spanned by the lattice coupling $\beta$ and the hopping and twisted mass parameters $\kappa$ and $\mu$, respectively, we obtain a comprehensive picture of the rich phase structure of the lattice theory. In particular, we verify the existence of an Aoki phase in the strong coupling region and the realization of the Sharpe-Singleton scenario at intermediate couplings. In the weak coupling region we identify the phase boundary for the physical finite temperature phase transition/crossover. Its shape in the three-dimensional parameter space is consistent with Creutz’s conjecture of a cone-shaped thermal transition surface.

We study a relation recently derived by K. Kondo at zero momentum between the Zwanziger’s horizon function, the ghost dressing function and Kugo’s functions $u$ and $w$. We agree with this result as far as bare quantities are considered. However, assuming the validity of the horizon gap equation, we argue that the solution $w(0)=0$ is not acceptable since it would lead to a vanishing renormalized ghost dressing function. On the contrary, when the cutoff goes to infinity, $u(0)\to \infty$, $w(0)\to -\infty$ such that $u(0)+w(0)\to -1$. Furthermore $w$ and $u$ are not multiplicatively renormalizable. Relaxing the gap equation allows $w(0)=0$ with $u(0)\to -1$. In both cases the bare ghost dressing function, $F(0,\Lambda )$, goes logarithmically to infinity at infinite cutoff. We show that, although the lattice results provide bare results not so different from the $F(0,\Lambda )=3$ solution, this is an accident due to the fact that the lattice cutoffs lie in the range $1–3{\mathrm{GeV}}^{-1}$. We show that the renormalized ghost dressing function should be finite and nonzero at zero momentum and can be reliably estimated on the lattice up to powers of the lattice spacing; from published data on a ${80}^4$ lattice at $\beta =5.7$ we obtain $F_R(0,\mu =1.5\mathrm{GeV})\simeq 2.2$.

We analyze meson-baryon scattering lengths in the framework of covariant baryon chiral perturbation theory at leading one-loop order. We compute the complete set of matching relations between the dimension-two low-energy constants in the two- and three-flavor formulations of the theory. We derive new two-flavor low-energy theorems for pion-hyperon scattering that can be tested in lattice simulations.

We discuss the possibility that the $X(3872)$ can be a hadronic $D{D}^{*}$ bound state in the framework of a potential model. The potential is generated by the exchange of pseudoscalar, scalar, and vector mesons resulting from the Lagrangian of heavy hadron chiral perturbation theory. The hadronic bound state configuration contains charged and neutral $D{D}^{*}$ components, while orbital $S$ and $D$ waves are included. Isospin symmetry breaking effects are fully taken into account. We show that binding in the $D{D}^{*}$ system with $J^{PC}=1^{++}$ already exists for a reasonable value of the meson-exchange regularization parameter of $\Lambda \sim 1.2\mathrm{GeV}$. We also explore the possibility of hadronic $B{B}^{*}$ bound states and show that binding can be achieved in the isoscalar limit for $J^{PC}=1^{++}$ or $1^{+-}$.

We observe the decays $D_{s1}^{*}(2710{)}^{+}\to D^{*}K$ and $D_{sJ}^{*}(2860{)}^{+}\to D^{*}K$ and measure their branching fractions relative to the $DK$ final state. We also observe, in the $D^{*}K$ mass spectrum, a new broad structure at a mass of $(3044\pm 8_{\mathrm{stat}}(\genfrac{}{}{0ex}{}{+30}{-5}{)}_{\mathrm{syst}})\mathrm{MeV}/c^2$ having a width $\Gamma =(239\pm {35}_{\mathrm{stat}}(\genfrac{}{}{0ex}{}{+46}{-42}{)}_{\mathrm{syst}})\mathrm{MeV}$. To obtain this result we use $470{\mathrm{fb}}^{-1}$ of data recorded by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage rings at the Stanford Linear Accelerator Center running at center-of-mass energies near 10.6 GeV.

We point out that mirror dark matter predicts low-energy ($E_R\lesssim 2\mathrm{keV}$) electron recoils from mirror electron scattering as well as nuclear recoils from mirror ion scattering. The former effect is examined and applied to the recently released low-energy electron recoil data from the CDMS Collaboration. We speculate that the sharp rise in electron recoils seen in CDMS below 2 keV might be due to mirror electron scattering and show that the parameters suggested by the data are roughly consistent with the mirror dark matter explanation of the annual modulation signal observed in the DAMA/Libra and DAMA/NaI experiments. Thus, the CDMS data offer tentative evidence supporting the mirror dark matter explanation of the DAMA experiments, which can be more rigorously checked by future low-energy electron recoil measurements.

$\mathcal{P}\mathcal{T}$-symmetrization of quantum graphs is proposed as an innovation where an adjustable, tunable nonlocality is admitted. The proposal generalizes the $\mathcal{P}\mathcal{T}$-symmetric square-well models of Ref. [M. Znojil, Phys. Rev. D 80, 045022 (2009).] (with real spectrum and with a variable fundamental length $\theta$) which are reclassified as the most elementary quantum $q$-pointed-star graphs with minimal $q=2$. Their equilateral $q=3,4,\dots$ generalizations are considered, with interactions attached to the vertices. Runge-Kutta discretization of coordinates simplifies the quantitative analysis by reducing our graphs to star-shaped lattices of $N=qK+1$ points. The resulting bound-state spectra are found real in an $N$-independent interval of couplings $\lambda \in (-1,1)$. Inside this interval the set of closed-form metrics ${\Theta }_j^{(N)}(\lambda )$ is constructed, defining independent eligible local (at $j=0$) or increasingly nonlocal (at $j=1,2,\dots$) inner products in the respective physical Hilbert spaces of states ${\mathcal{H}}_j^{(N)}(\lambda )$. In this way each graph is assigned a menu of nonequivalent, optional probabilistic quantum interpretations.

We evaluate the Casimir energy and force for a massive fermionic field in the geometry of two parallel plates on background of Minkowski spacetime with an arbitrary number of toroidally compactified spatial dimensions. The bag boundary conditions are imposed on the plates and periodicity conditions with arbitrary phases are considered along the compact dimensions. The Casimir energy is decomposed into purely topological, single plate and interaction parts. With independence of the lengths of the compact dimensions and the phases in the periodicity conditions, the interaction part of the Casimir energy is always negative. In order to obtain the resulting force, the contributions from both sides of the plates must be taken into account. Then, the forces coming from the topological parts of the vacuum energy cancel out and only the interaction term contributes to the Casimir force. Applications of the general formulae to Kaluza-Klein-type models and carbon nanotubes are given. In particular, we show that for finite-length metallic nanotubes, the Casimir forces acting on the tube edges are always attractive, whereas for semiconducting-type ones, they are attractive for small lengths of the nanotube and repulsive for large lengths.

In loop quantum gravity the classical point of departure is the Einstein-Hilbert action modified by the addition of the so-called Holst term. Classically, this term does not affect the equations of motion, but it induces a well-known quantization ambiguity in the quantum theory, parametrized by the Barbero-Immirzi parameter. Recently, it has been suggested to promote the Barbero-Immirzi parameter to a field. The resulting theory, obtainable starting from the usual Holst action, is general relativity coupled to a pseudoscalar field. However, this theory turns out to have an unconventional kinetic term for the Barbero-Immirzi field and a rather unnatural coupling with fermions. The main goal of this work is twofold: First, to propose a further generalization of the Holst action, which yields a theory of gravity and matter with a more natural coupling to the Barbero-Immirzi field; second, to study the possible implications for cosmology correlated to the existence of this new pseudoscalar field.

We study the growth of subhorizon perturbations in brane-induced gravity using perturbation theory. We solve for the linear evolution of perturbations taking advantage of the symmetry under gauge transformations along the extra-dimension to decouple the bulk equations in the quasistatic approximation, which we argue may be a better approximation at large scales than thought before. We then study the nonlinearities in the bulk and brane equations, concentrating on the workings of the Vainshtein mechanism by which the theory becomes general relativity (GR) at small scales. We show that at the level of the power spectrum, to a good approximation, the effect of nonlinearities in the modified gravity sector may be absorbed into a renormalization of the gravitational constant. Since the relation between the lensing potential and density perturbations is entirely unaffected by the extra physics in these theories, the modified gravity can be described in this approximation by a single function, an effective gravitational constant for nonrelativistic motion that depends on space and time. We develop a resummation scheme to calculate it, and provide predictions for the nonlinear power spectrum. At the level of the large-scale bispectrum, the leading order corrections are obtained by standard perturbation theory techniques, and show that the suppression of the brane-bending mode leads to characteristic signatures in the non-Gaussianity generated by gravity, generic to models that become GR at small scales through second-derivative interactions. We compare the predictions in this work to numerical simulations in a companion paper.

We use $N$-body simulations to study the nonlinear structure formation in brane-induced gravity, developing a new method that requires alternate use of Fast Fourier Transforms and relaxation. This enables us to compute the nonlinear matter power spectrum and bispectrum, the halo mass function, and the halo bias. From the simulation results, we confirm the expectations based on analytic arguments that the Vainshtein mechanism does operate as anticipated, with the density power spectrum approaching that of standard gravity within a modified background evolution in the nonlinear regime. The transition is very broad and there is no well defined Vainshtein scale, but roughly this corresponds to $k_{*}\simeq 2h{\mathrm{Mpc}}^{-1}$ at redshift $z=1$ and $k_{*}\simeq 1h{\mathrm{Mpc}}^{-1}$ at $z=0$. We checked that while extrinsic curvature fluctuations go nonlinear, and the dynamics of the brane-bending mode $C$ receives important nonlinear corrections, this mode does get suppressed compared to density perturbations, effectively decoupling from the standard gravity sector. At the same time, there is no violation of the weak field limit for metric perturbations associated with $C$. We find good agreement between our measurements and the predictions for the nonlinear power spectrum presented in paper I, that rely on a renormalization of the linear spectrum due to nonlinearities in the modified gravity sector. A similar prediction for the mass function shows the right trends. Our simulations also confirm the induced change in the bispectrum configuration dependence predicted in paper I.

We present and analyze a gauge-invariant quantum theory of the Friedmann-Robertson-Walker universe with dust. We construct the reduced phase space spanned by gauge-invariant quantities by using the so-called relational formalism at the classical level. The reduced phase space thereby obtained can be quantized in the same manner as an ordinary mechanical system. We carry out the quantization and obtain the Schrödinger equation. This quantization procedure realizes a possible resolution to the problem of time and observables in canonical quantum gravity. We analyze the classical initial singularity of the theory by evolving a wave packet backward in time and evaluating the expectation value of the scale factor. It is shown that the initial singularity of the Universe is avoided by the quantum gravitational effects.

We constrain the one-parameter ($\alpha$) class of TeVeS models by testing the theory against both rotation curve and strong gravitational lensing data on galactic scales, remaining fully relativistic in our formalism. The upshot of our analysis is that—at least in its simplest original form, which is the only one studied in the literature so far—TeVeS is ruled out, in the sense that the models cannot consistently fit simultaneously the two sets of data without including a significant dark matter component. It is also shown that the details of the underlying cosmological model are not relevant for our analysis, which pertains to galactic scales. The choice of the stellar initial mass function—which affects the estimates of baryonic mass—is found not to change our conclusions.

The MAGIC Collaboration has provided new observational data pertaining to the TeV J2032+4130 gamma-ray source (within the Cygnus OB2 region), for energies $E_{\gamma }>400\mathrm{GeV}$. It is then appropriate to update the impact of these data on gamma-ray production mechanisms in stellar associations. We consider two mechanisms of gamma-ray emission, pion production and decay (PION) and photoexcitation of high-energy nuclei followed by prompt photoemission from the daughter nuclei ($A^{\star }$). We find that while the data can be accommodated with either scenario, the $A^{\star }$ features a spectral bump, corresponding to the threshold for exciting the giant dipole resonance, which can serve to discriminate between them. We comment on neutrino emission and detection from the region if the PION and/or $A^{\star }$ processes are operative. We also touch on the implications for this analysis of future Fermi and Čerenkov Telescope array data.

The exchange of electroweak gauginos in the $t$ or $u$ channel allows squark pair production at hadron colliders without color exchange between the squarks. This can give rise to events where little or no energy is deposited in the detector between the squark decay products. We discuss the potential for detection of such rapidity-gap events at the Large Hadron Collider. Our numerical analysis is divided into two parts. First, we evaluate in a simplified framework the rapidity-gap signal at the parton level. The second part covers an analysis with full event simulation using PYTHIA as well as Herwig++, but without detector simulation. We analyze the transverse energy deposited between the jets from squark decay, as well as the probability of finding a third jet in between the two hardest jets. For the minimal supergravity benchmark point SPS1a we find statistically significant evidence for a color-singlet exchange contribution. The systematical differences between current versions of PYTHIA and HERWIG++ are larger than the physical effect from color-singlet exchange; however, these systematic differences could be reduced by tuning both Monte Carlo generators on normal QCD dijet data.

The little hierarchy problem encountered in the constrained minimal supersymmetric model can be ameliorated in supersymmetric models based on the gauge symmetry $G_{422}\equiv SU(4{)}_c\times SU(2{)}_L\times SU(2{)}_R$. The standard assumption in the constrained minimal supersymmetric model [and in $SU(5)$ and $SO(10)$] of universal gaugino masses can be relaxed in $SU(4{)}_c\times SU(2{)}_L\times SU(2{)}_R$, and this leads to a significant improvement in the degree of fine-tuning required to implement radiative electroweak breaking in the presence of a characteristic supersymmetry breaking scale of around a TeV. Examples of Higgs and sparticle mass spectra realized with 10% fine-tuning are presented.