Gaussian processes provide a method for extracting cosmological information from observations without assuming a cosmological model. We carry out cosmography—mapping the time evolution of the cosmic expansion—in a model-independent manner using kinematic variables and a geometric probe of cosmology. Using the state of the art supernova distance data from the Union2.1 compilation, we constrain, without any assumptions about dark energy parametrization or matter density, the Hubble parameter and deceleration parameter as a function of redshift. Extraction of these relations is tested successfully against models with features on various coherence scales, subject to certain statistical cautions.

The characterization of dark energy is one of the primary goals in cosmology especially now that many new experiments are being planned with the aim of reaching a high sensitivity on cosmological parameters. It is known that if we move away from the simple cosmological constant model then we need to consider perturbations in the dark energy fluid. This means that dark energy has two extra degrees of freedom: the sound speed $c_s^2$ and the anisotropic stress $\sigma$. If dark energy is inhomogenous at the scales of interest then the gravitational potentials are modified and the evolution of the dark matter perturbations is also directly affected. In this paper we add an anisotropic component to the dark energy perturbations. Following the idea introduced in D. Sapone and M. Kunz, Phys. Rev. D 80, 083519 (2009), we solve analytically the equations of perturbations in the dark sector, finding simple and accurate approximated solutions. We also find that the evolution of the density perturbations is governed by an effective sound speed that depends on both the sound speed and the anisotropic stress parameter. We then use these solutions to look at the impact of the dark energy perturbations on the matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background.

There might be a light scalar field during inflation which is not responsible for the accelerating inflationary expansion. Then, its quantum fluctuation is stretched during inflation. This scalar field could be a curvaton, if it decays at a late time. In addition, if the inflaton decay rate depends on the light scalar field expectation value by interactions between them, density perturbations could be generated by the quantum fluctuation of the light field when the inflaton decays. This is a modulated reheating mechanism. We study curvature perturbation in models where a light scalar field does not only play a role of curvaton but also induce modulated reheating at the inflaton decay. We calculate the nonlinearity parameters as well as the scalar spectral index and the tensor-to-scalar ratio. We find that there is a parameter region where nonlinearity parameters are also significantly enhanced by the cancellation between the modulated effect and the curvaton contribution. For the simple quadratic potential model of both inflaton and curvaton, both tensor-to-scalar ratio and nonlinearity parameters could be simultaneously large.

It has been claimed in a recent paper [J. D. Barrow, A. B. Batista, J. C. Fabris, M. J. S. Houndjo, and G. Dito, Phys. Rev. D 84, 123518 (2011).] that sudden singularities will survive in semiclassical gravity. This issue is here carefully reviewed, pointing out that such conclusion, even if valid under some specific conditions, does not stand in other cases. An explicit example is studied in detail to support our statement, stemming from these other situations, that quantum effects may in fact drastically modify the behavior of sudden singularities.

Constraining theoretical models, which are represented by a set of parameters, using observational data is an important exercise in cosmology. In Bayesian framework this is done by finding the probability distribution of parameters which best fits to the observational data using sampling based methods like Markov chain Monte Carlo (MCMC). It has been argued that MCMC may not be the best option in certain problems in which the target function (likelihood) poses local maxima or have very high dimensionality. Apart from this, there may be examples in which we are mainly interested to find the point in the parameter space at which the probability distribution has the largest value. In this situation the problem of parameter estimation becomes an optimization problem. In the present work we show that particle swarm optimization (PSO), which is an artificial intelligence inspired population based search procedure, can also be used for cosmological parameter estimation. Using PSO we were able to recover the best-fit $\Lambda$ cold dark matter (LCDM) model parameters from the WMAP seven year data without using any prior guess value or any other property of the probability distribution of parameters like standard deviation, as is common in MCMC. We also report the results of an exercise in which we consider a binned primordial power spectrum (to increase the dimensionality of problem) and find that a power spectrum with features gives lower chi square than the standard power law. Since PSO does not sample the likelihood surface in a fair way, we follow a fitting procedure to find the spread of likelihood function around the best-fit point.

Matched-filter searches for gravitational waves from coalescing compact binaries by the LIGO Scientific Collaboration use the FINDCHIRP algorithm: an implementation of the optimal filter with innovations to account for unknown signal parameters and to improve performance on detector data that has nonstationary and non-Gaussian artifacts. We provide details on the FINDCHIRP algorithm as used in the search for subsolar mass binaries, binary neutron stars, neutron star–black hole binaries, and binary black holes.

Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein’s theory of gravity are determined by the scalar mass $m_s$ and by a Brans-Dicke-like coupling parameter ${\omega }_{\mathrm{BD}}$. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set lower bounds on ${\omega }_{\mathrm{BD}}$ and upper bounds on the combination $m_s/\sqrt{{\omega }_{\mathrm{BD}}}$. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio $\rho$ would yield $(m_s/\sqrt{{\omega }_{\mathrm{BD}}})(\rho /10)\lesssim {10}^{-15}$, ${10}^{-16}$, and ${10}^{-19}\mathrm{eV}$ for Advanced LIGO, ET, and eLISA, respectively. A statistical combination of multiple observations may further improve these bounds.

We reexamine the $R$-parity violating contribution to the fermion electric and chromo-electric dipole moments in the two-loop diagrams. It is found that the leading Barr-Zee-type two-loop contribution is smaller than the result found in previous works, and that electric dipole moment experimental data provide looser limits on $R$-parity violating couplings.

We study multipole decompositions of the electromagnetic currents of spin-$1/2$, 1, and $3/2$ particles described in terms of representation-specific wave equations which are second order in the momenta and which emerge within the recently elaborated Poincaré covariant-projector method, where the respective Lagrangians explicitly depend on the Lorentz group generators of the representations of interest. The currents are then the ordinary linear Noether currents related to phase invariance, and present themselves always as two-terms motion–plus spin-magnetization currents. The spin-magnetization currents appear weighted by the gyromagnetic ratio $g$, a free parameter in the method which we fix either by unitarity of forward Compton scattering amplitudes in the ultraviolet for spin-1 and spin-$3/2$, or in the spin-$1/2$ case, by their asymptotic vanishing, thus ending up in all three cases with the universal $g$ value of $g=2$. Within the method under discussion, we calculate the electric multipoles of the above spins for the spinor, the four-vector, and the four-vector–spinor representations, and find it favorable in some aspects, specifically in comparison with the conventional Proca and Rarita-Schwinger frameworks. We furthermore attend to the most general non-Lagrangian spin-$3/2$ currents, which are allowed by Lorentz invariance to be up to third order in the momenta and construct the linear-current equivalent of identical multipole moments of one of them. We conclude that nonlinear non-Lagrangian spin-$3/2$ currents are not necessarily more general and more advantageous than the linear spin-$3/2$ Lagrangian current emerging within the covariant-projector formalism. Finally, we test the representation dependence of the multipoles by placing spin-1 and spin-$3/2$ in the respective $(1,0)\oplus (0,1)$ and $(3/2,0)\oplus (0,3/2)$ single-spin representations. We observe representation independence of the charge monopoles and the magnetic dipoles, in contrast to the higher multipoles, which turn out to be representation-dependent. In particular, we find the bi-vector $(1,0)\oplus (0,1)$ to be characterized by an electric quadrupole moment of opposite sign to the one found in $(1/2,1/2)$, and consequently to the $W$ boson. This observation allows us to explain the positive electric quadrupole moment of the $\rho$ meson extracted from recent analyses of the $\rho$ meson electric form factor. Our finding points toward the possibility that the $\rho$-meson could transform as part of an antisymmetric tensor with an $a_1$ mesonlike state as its representation companion, a possibility consistent with the empirically established $\rho$ and $a_1$ vector meson dominance of the hadronic vector and axial-vector currents.

The magnetic interactions between a fermion and an antifermion of opposite electric or color charges in the ${}^{1}S_0^{-+}$ and ${}^{3}P_0^{++}$ states with $J=0$ are very attractive and singular near the origin and may allow the formation of new bound and resonance states at short distances. In the two-body Dirac equations formulated in constraint dynamics, the short-distance attraction for these states for point particles leads to a quasipotential that behaves near the origin as $-{\alpha }^2/r^2$, where $\alpha$ is the coupling constant. Representing this quasipotential at short distances as $\lambda (\lambda +1)/r^2$ with $\lambda =(-1+\sqrt{1-4{\alpha }^2})/2$, both ${}^{1}S_0^{-+}$ and ${}^{3}P_0^{++}$ states admit two types of eigenstates with drastically different behaviors for the radial wave function $u=r\psi$. One type of states, with $u$ growing as $r^{\lambda +1}$ at small $r$, will be called usual states. The other type of states with $u$ growing as $r^{-\lambda }$ will be called peculiar states. Both of the usual and peculiar eigenstates have admissible behaviors at short distances. Remarkably, the solutions for both sets of ${}^{1}S_0$ states can be written out analytically. The usual bound ${}^{1}S_0$ states possess attributes the same as those one usually encounters in QED and QCD, with bound QED state energies explicitly agreeing with the standard perturbative results through order ${\alpha }^4$. In contrast, the peculiar bound ${}^{1}S_0$ states, yet to be observed, not only have different behaviors at the origin, but also distinctly different bound state properties (and scattering phase shifts). For the peculiar ${}^{1}S_0$ ground state of fermion-antifermion pair with fermion rest mass $m$, the root-mean-square radius is approximately $1/m$, binding energy is approximately $(2-\sqrt{2})m$, and rest mass approximately $\sqrt{2}m$. On the other hand, the $(n+1){}^{1}S_0$ peculiar state with principal quantum number ($n+1$) is nearly degenerate in energy and approximately equal in size with the $n{}^{1}S_0$ usual states. For the ${}^{3}P_0$ states, the usual solutions lead to the standard bound state energies and no resonance, but resonances have been found for the peculiar states whose energies depend on the description of the internal structure of the charges, the mass of the constituent, and the coupling constant. The existence of both usual and peculiar eigenstates in the same system leads to the non-self-adjoint property of the mass operator and two nonorthogonal complete sets. As both sets of states are physically admissible, the mass operator can be made self-adjoint with a single complete set of admissible states by introducing a new peculiarity quantum number and an enlarged Hilbert space that contains both the usual and peculiar states in different peculiarity sectors. Whether or not these newly-uncovered quantum-mechanically acceptable peculiar ${}^{1}S_0$ bound states and ${}^{3}P_0$ resonances for point fermion-antifermion systems correspond to physical states remains to be further investigated.

We show that supersymmetric models with a large Dirac gluino mass can evade much of the jets plus missing energy searches at the LHC. Dirac gaugino masses arise from “supersoft” operators that lead to finite one-loop suppressed contributions to the scalar masses. A little hierarchy between the Dirac gluino mass 5–10 times heavier than the squark masses is automatic and technically natural, in stark contrast to supersymmetric models with Majorana gaugino masses. At the LHC, colored sparticle production is suppressed not only by the absence of gluino pair (or associated) production, but also because several of the largest squark pair production channels are suppressed or absent. We recast the null results from the present jets plus missing energy searches at the LHC for supersymmetry onto a supersoft supersymmetric simplified model. Assuming a massless lightest supersymmetric particle, we find the strongest bounds are as follows: 748 GeV from a $2j+{\mathrm{E̸}}_T$ search at ATLAS ($4.7{\mathrm{fb}}^{-1}$) and 684 GeV from a combined jets plus missing energy search using ${\alpha }_T$ at CMS ($1.1{\mathrm{fb}}^{-1}$). In the absence of a future observation, we estimate the bounds on the squark masses to improve only modestly with increased luminosity. We also briefly consider the further weakening in the bounds as the lightest supersymmetric particle mass is increased.

We investigate the expectations for the light Higgs signal in the minimal supersymmetric standard model in different search channels at the LHC. After taking into account dark matter and flavor constraints in the minimal supersymmetric standard model with 11 free parameters as well as LHC results on the Higgs sector, we show that the light Higgs signal in the $\gamma \gamma$ channel is expected to be at most at the level of the standard model Higgs, while the $h\to b\overline{b}$ from $W$ fusion and/or the $h\to \tau \overline{\tau }$ can be enhanced. For the main discovery mode, we show that a strong suppression of the signal occurs in two different cases: low $M_A$ or large invisible width. The former is however strongly constrained by the recent LHC results. A more modest suppression is associated with the effect of light supersymmetric particles. Looking for such modification of the Higgs properties and searching directly for supersymmetric partners and pseudoscalar Higgs offer two complementary probes of supersymmetry at the LHC.

We consider the position of the deconfining critical endpoint, where the first order transition for deconfinement is washed out by the presence of massive, dynamical quarks. We use an effective matrix model, employed previously to analyze the transition in the pure glue theory. If the parameters of the pure glue theory are unaffected by the presence of dynamical quarks, and if the quarks only contribute perturbatively, then for three colors and three degenerate quark flavors this quark mass is very heavy, $m^{\mathrm{de}}\sim 2.5\mathrm{GeV}$, while the critical temperature $T_{\mathrm{de}}$ barely changes, $\sim 1\%$ below that in the pure glue theory. The location of the deconfining critical endpoint is a sensitive test to differentiate between effective models. For example, models with a logarithmic potential for the Polyakov loop give much smaller values of the quark mass, $m^{\mathrm{de}}\sim 1\mathrm{GeV}$, and a large shift in $T_{\mathrm{de}}\sim 10\%$ lower than that in the pure glue theory.

The recent lattice calculation at finite axial chemical potential suggests that the induced current density of the chiral magnetic effect (CME) is somehow suppressed compared with the standard analytical formula. We show in a Nambu-Jona-Lasino-type model of QCD that such a suppression is a natural result when considering the influence of the attractive axial-vector interaction. We point out that the lattice result does not need to be quantitatively consistent with the analytical formula due to the chirality density-density correlation. We also investigate the nonperturbative effect of instanton molecules on the CME. Since an unconventional repulsive axial-vector interaction is induced, the CME will be enhanced significantly by the instanton-anti-instanton pairings. Such a prediction needs to be tested by more improved lattice simulations. We further demonstrate that the axial-vector interaction plays an important role on the $T-{\mu }_A$ phase diagram.

We study the effect of sigma meson on the $D_1(2430)\to D\pi \pi$ decay by constructing an effective Lagrangian preserving the chiral symmetry and the heavy quark symmetry. The sigma meson is included through a linear sigma model, in which both the $q\overline{q}$ and $qq\overline{q}\overline{q}$ states are incorporated respecting their different $U(1{)}_A$ transformation properties. We first fit the sigma meson mass and $\sigma \mathrm{\text{−}}\pi \mathrm{\text{−}}\pi$ coupling constant to the $I=0$, $S$-wave $\pi \mathrm{\text{−}}\pi$ scattering data. Then, we show how the differential decay width $d\Gamma (D_1\to D(\pi \pi {)}_{I=0,L=0})/d{m}_{\pi \pi }$ depends on the quark structure of the sigma meson. We find that our study, combing with the future data, can give a clue to understand the sigma meson structure.

We discuss the single transverse-spin asymmetry (SSA) to be observed in the $D$-meson production with large transverse-momentum in semi-inclusive deep inelastic scattering, $e{p}^{\uparrow }\to eDX$. This contribution is embodied as a twist-3 mechanism in the collinear factorization, which is induced by purely gluonic correlation inside the transversely-polarized nucleon, in particular, by the three-gluon correlation effects. The complete formula for the corresponding SSA in the leading-order QCD is expressed in terms of the four independent gluonic correlation functions and reveals the five independent structures with respect to the dependence on the azimuthal angle for the produced $D$-meson. We present the numerical calculations of the SSA formula at the kinematics relevant to a future electron-ion collider.

The production of leading neutrons in deep-inelastic scattering is usually considered as a tool to measure the pion structure function at small $x$ accessible at HERA. The main obstacle is the lack of reliable evaluations of the absorption corrections, which significantly suppress the cross section. We performed a parameter-free calculation within the dipole approach and found the absorption corrections to be nearly as strong, as for neutron production in $pp$ collisions. We also included the significant contribution of the isovector Reggeons with natural ($\rho$, $a_2$) and unnatural ($a_1$, $\rho \mathrm{\text{−}}\pi$ cut) parity with parameters constrained by phenomenology. With a certain modeling for the pion-to-proton ratio of the structure functions we reached good agreement with data from the ZEUS and H1 experiments, successfully reproducing the observed dependences on the fractional neutron momentum $z$, the photon virtuality $Q^2$, and the transverse momentum transfer $q_T$.

Scalar color octets are generic signals for new physics at LHC energies. We examine their pair production at the LHC to next-to-leading-order QCD. This computation serves as another test of the fully automized MadGolem framework. We find large NLO production rates and sizeable quantum effects which depend on the sgluon mass. The shift in the sgluon distributions is mild and in good agreement with a multijet merging calculation.

Neutrinos streaming from a supernova core occasionally scatter in the envelope, producing a small “neutrino halo” with a much broader angle distribution than the primary flux originating directly from the core. Cherry et al. have recently pointed out that, during the accretion phase, the halo actually dominates neutrino-neutrino refraction at distances exceeding some 100 km. However, the multiangle matter effect (which increases if the angle distribution is broader) still appears to suppress self-induced flavor conversion during the accretion phase.