We study the formation of large-scale structure in universes dominated by dark matter and driven to accelerated expansion by $f(R)$ gravity in the Palatini formalism. If the dark matter is cold, practically all of these models are ruled out because they fail to reproduce the observed matter power spectrum. We point out that if the assumption that dark matter is perfect and pressureless at all scales is relaxed, nontrivial alternatives to a cosmological constant become viable within this class of modified gravity models.

We explore extensions of hybrid inflationary models in the context of supersymmetric $D$-term inflation. We point out that a large variety of inflationary scenarios can be encountered when the field content is extended. It is not only possible to get curvaton type models but also scenarios in which different fields, with nontrivial statistical properties, contribute to the primordial curvature fluctuations. We explore more particularly the parameter space of these multiple-field inflationary models. It is shown that there exists a large domain in which significant primordial non-Gaussianities can be produced while preserving a scale free power spectrum for the metric fluctuations. In particular we explicitly compute the expected bispectrum and trispectrum for such models and compared the results to the current and expected observational constraints. It is shown that it is necessary to use both the bispectra and trispectra of cosmic microwave background anisotropies to efficiently reduce their parameter space.

We study the effect of the cosmological constant $\Lambda$ on the bending of light by a concentrated spherically symmetric mass. Contrarily to previous claims, we show that, when the Schwarzschild-de Sitter geometry is taken into account, $\Lambda$ does indeed contribute to the bending.

Although the rocket-based x-ray quantum calorimetry (XQC) experiment was designed for x-ray spectroscopy, the minimal shielding of its calorimeters, its low atmospheric overburden, and its low-threshold detectors make it among the most sensitive instruments for detecting or constraining strong interactions between dark matter particles and baryons. We use Monte Carlo simulations to obtain the precise limits the XQC experiment places on spin-independent interactions between dark matter and baryons, improving upon earlier analytical estimates. We find that the XQC experiment rules out a wide range of nucleon-scattering cross sections centered around 1 b for dark matter particles with masses between 0.01 and ${10}^5\mathrm{GeV}$. Our analysis also provides new constraints on cases where only a fraction of the dark matter strongly interacts with baryons.

We consider examples of $D=4$ string theory vacua which, although globally nongeometric, admit a local description in terms of $D=10$ supergravity backgrounds. We analyze such backgrounds and find that the supersymmetry spinors vary nontrivially along the internal manifold, reproducing the interpolating supergravity solutions found by Frey and Graña. Finally, we propose a simple, local expression for nongeometric fluxes in terms of the internal spinors of the compactification.

In the framework of effective field theory we show that, at two-loop order, the mass and width of the $\Delta$ resonance defined via the (relativistic) Breit-Wigner parametrization both depend on the choice of field variables. In contrast, the complex-valued position of the pole of the propagator is independent of this choice.

Four-quark states with different internal clusters are discussed within the constituent quark model. It is pointed out that the diquark concept is not meaningful in the construction of a tetraquark interpolating current in the QCD sum-rule approach, and hence existing sum-rule studies of four-quark states are incomplete. An updated QCD sum-rule determination of the properties of diquark clusters is then used as input for the constituent quark model to obtain the masses of light $0^{++}$ tetraquark states (i.e. a bound state of two diquark clusters). The results support the identification of $\sigma (600)$, $f_0(980)$, and $a_0(980)$ as the $0^{++}$ light tetraquark states, and seem to be inconsistent with the tetraquark state interpretation of the new BES observations of the near-threshold $p\overline{p}$ enhancements, $X(1835)$ and $X(1812)$, with the possible exception that $X(1576)$ may be an exotic first orbital excitation of $f_0(980)$ or $a_0(980)$.

The SU(3) simplest little Higgs model in its original framework without the so-called $\mu$ term inevitably involves a massless pseudoscalar boson $\eta$, which is problematic for $b$ physics and the cosmological axion limit. With the $\mu$ term introduced by hand, the $\eta$ boson acquires mass $m_{\eta }\sim \mu$, which can be lighter than half the Higgs boson mass in a large portion of the parameter space. In addition, the introduced $\mu$ term generates sizable coupling of $H\mathrm{\text{−}}\eta \mathrm{\text{−}}\eta$. The Higgs boson can dominantly decay into a pair of $\eta$’s especially when $m_H$ is below the $WW$ threshold. Another new decay channel of $H\to Z\eta$ can be dominant or compatible with $H\to W^{+}{W}^{-}$ for $m_H$ above the $Z\eta$ threshold. We show that the LEP bound on the Higgs boson mass is loosened to some extent due to this new $H\to \eta \eta$ decay channel as well as the reduced coupling of $H\mathrm{\text{−}}Z\mathrm{\text{−}}Z$. The Higgs boson mass bound falls to about 110 GeV for $f=3–4\mathrm{TeV}$. Since the $\eta$ boson decays mainly into a $b\overline{b}$ pair, $H\to \eta \eta \to 4b$ and $H\to Z\eta \to Zb\overline{b}$ open up other interesting search channels in the pursuit of the Higgs boson in the future experiments. We discuss these issues.

The effects of unquenching on the perturbative improvement coefficients in the Symanzik action are computed within the framework of Lüscher-Weisz on-shell improvement. We find that the effects of quark loops are surprisingly large, and their omission may well explain the scaling violations observed in some unquenched studies.

The unpolarized, helicity, and transversity distributions of quarks in the proton are calculated in the overlap representation of light-cone wave functions truncated to the lowest order Fock-space components with three valence quarks. The three distributions at the hadronic scale satisfy an interesting relation consistent with the Soffer inequality. Results are derived in a relativistic quark model including evolution up to the next-to-leading order. Predictions for the double transverse-spin asymmetry in Drell-Yan dilepton production initiated by proton-antiproton collisions are presented. Asymmetries of about 20%–30% are found in the kinematic conditions of the $\mathcal{P}\mathcal{A}\mathcal{X}$ experiment.

Diffractive production of heavy flavors is calculated within the light-cone dipole approach. Novel leading twist mechanisms are proposed, which involve both short and long transverse distances inside the incoming hadron. Nevertheless, the diffractive cross section turns out to be sensitive to the primordial transverse momenta of projectile gluons, rather than to the hadronic size. Our calculations agree with the available data for diffractive production of charm and beauty, and with the observed weak variation of the diffraction-to-inclusive cross section ratios as function of the hard scale.

We report a comprehensive set of results for $B$-meson heavy-to-light transition form factors calculated using a truncation of, and expression for, the transition amplitudes in which all elements are motivated by the study of Dyson-Schwinger equations in QCD. In this relativistic approach, which realizes confinement and dynamical chiral symmetry breaking, all physical values of momentum transfer in the transition form factors are simultaneously accessible. Our results can be useful in the analysis and correlation of the large body of data being accumulated at extant facilities, and thereby in probing the standard model and beyond.

Neutrino coherent scattering cross sections can be as large as ${10}^{-39}{\mathrm{cm}}^2$, while current dark matter experiments have sensitivities to WIMP coherent scattering cross sections 5 orders of magnitude smaller; future experiments plan to have sensitivities to cross sections as small as ${10}^{-48}{\mathrm{cm}}^2$. With large target masses and few keV recoil energy detection thresholds, neutral current coherent scattering of solar neutrinos becomes an irreducible background in dark matter searches. In the current zero-background analysis paradigm, neutrino coherent scattering will limit the achievable sensitivity to dark matter scattering cross sections, at the level of ${10}^{-46}{\mathrm{cm}}^2$.

We study the possibility of binding eight quarks in a molecular hadronic system composed of two nucleons and an antikaon, with the quantum numbers of a hexaquark flavor, in particular, with strangeness $-1$, isospin $1/2$, parity -, baryonic number 2, and two possible spins, 0 or 1. We discuss the possible production of this hadron in the experiments which are presently investigating hot topics like the ${\Theta }^{+}$ pentaquark or the $K^{-}$ deeply bound in nuclei. The $K^{-}•N$ interactions and the coupling to other channels are computed microscopically from a confining and chiral invariant quark model resulting in local plus separable Gaussian potentials. The $N•N$ interactions used here are the state of the art Nijmegen potentials. The binding energy and the decay rate of the $K^{-}•N$ and $K^{-}•N•N$ systems are computed with configuration space variational methods.

We update the extraction of $|V_{ub}|$ from exclusive semileptonic $B\to \pi$ decays, combining experimental partial branching fraction information with theoretical form-factor calculations, using the recently revised HPQCD results for the form factors $f_{+}$ and $f_0$. We use Omnès representations to provide the required parametrizations of the form factors. The extracted value is $|V_{ub}|=(3.47\pm 0.29\pm 0.03)\times {10}^{-3}$, in striking agreement with $|V_{ub}|$ extracted using all other inputs in CKM fits and showing some disagreement with $|V_{ub}|$ extracted from inclusive semileptonic $B\to \pi$ decays.

I consider two-level detectors, coupled to a quantum scalar field, moving inside cavities. I highlight some pathological resonant effects due to abrupt boundaries, and decide to describe the cavity by switching smoothly the interaction by a time-dependent gatelike function. Considering uniformly accelerated trajectories, I show that some specific choices of nonadiabatic switching have led to hazardous interpretations about the enhancement of the Unruh effect in cavities. More specifically, I show that the emission/absorption ratio takes arbitrary high values according to the emitted quanta properties and to the transients undergone at the entrance and the exit of the cavity, independently of the acceleration. An explicit example is provided where I show that inertial and uniformly accelerated worldlines can even lead to the same “pseudotemperature.” In passing, I also compute the deviation from the exact thermal response for a finite size cavity.

In many versions of the brane model, the modulus field of extra dimensions, the radion, could have cosmological evolution, which induces a variation of the Higgs vacuum expectation value, $⟨H⟩$, resulting in a cosmological variation of the electron mass $m_e$. The formation of cosmic microwave background (CMB) anisotropies is thus affected, causing changes both in the peak positions and amplitudes in the CMB power spectra. Using the three-year Wilkinson Microwave Anisotropy Probe (WMAP) CMB data, with the Hubble parameter $H_0$ fixed to be the Hubble Space Telescope (HST) result $72\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$, we obtain a constraint on $\rho$, the ratio of the value of $⟨H⟩$ at CMB recombination to its present value, to be [0.97, 1.02].

Overlap fermions have an exact chiral symmetry on the lattice and are thus an appropriate tool for investigating the chiral and topological structure of the QCD vacuum. We study various chiral and topological aspects of quenched gauge field configurations. This includes the localization and chiral properties of the eigenmodes, the local structure of the ultraviolet-filtered field strength tensor, as well as the structure of topological charge fluctuations. We conclude that the vacuum has a multifractal structure.