Drell-Yan pair production is investigated. We reexamine a model where the quark momentum fraction is defined as the ratio of the corresponding light-cone components of the quark and parent nucleon in a naive parton-model approach. It is shown that the results differ from the standard parton model. This is due to unphysical solutions for the momentum fractions within the naive approach which are not present in the standard parton model. In a calculation employing full quark kinematics, i.e., including primordial quark transverse momentum, these solutions also appear. A prescription is given to handle these solutions in order to avoid incorrect results. The impact of these solutions in the full kinematical approach is demonstrated and compared to the modified result.

We investigate the bounds on axionlike states from flavor-changing neutral current $b\to s$ decays, assuming the axion couples to the standard model through mixing with the Higgs sector. Such GeV-scale axions have received renewed attention in connection with observed cosmic ray excesses. We find that existing $B\to K{\ell }^{+}{\ell }^{-}$ data impose stringent bounds on the axion decay constant in the multi-TeV range, relevant for constraining the “axion portal” model of dark matter. Such bounds also constrain light Higgs scenarios in the next-to-minimal supersymmetric standard model. These bounds can be improved by dedicated searches in $B$-factory data and at LHCb.

Dark matter, baryonic matter, and dark energy have different properties but contribute comparable energy density to the present Universe. We point out that they may have a common origin. As the dark energy has a scale far lower than all known scales in particle physics but very close to neutrino masses, while the excess matter over antimatter in the baryonic sector is probably related to the neutrino-mass generation, we unify the origin of the dark and visible universe in a variant of the seesaw model. In our model (i) the dark matter relic density is a dark matter asymmetry emerged simultaneously with the baryon asymmetry from leptogenesis; (ii) the dark energy is due to a pseudo-Nambu-Goldstone-Boson associated with the neutrino-mass generation.

We study the evolution of cosmological perturbations in $f(\mathcal{G})$ gravity, where the Lagrangian is the sum of a Ricci scalar $R$ and an arbitrary function $f$ in terms of a Gauss-Bonnet term $\mathcal{G}$. We derive the equations for perturbations assuming matter to be described by a perfect fluid with a constant equation of state $w$. We show that density perturbations in perfect fluids exhibit negative instabilities during both the radiation and the matter domination, irrespective of the form of $f(\mathcal{G})$. This growth of perturbations gets stronger on smaller scales, which is difficult to be compatible with the observed galaxy spectrum unless the deviation from general relativity is very small. Thus $f(\mathcal{G})$ cosmological models are effectively ruled out from this ultraviolet instability, even though they can be compatible with the late-time cosmic acceleration and local gravity constraints.

A new model realization of the vector curvaton paradigm is presented and analyzed. The model consists of a single massive Abelian vector field, with a Maxwell-type kinetic term. By assuming that the kinetic function and the mass of the vector field are appropriately varying during inflation, it is shown that a scale-invariant spectrum of superhorizon perturbations can be generated. These perturbations can contribute to the curvature perturbation of the Universe. If the vector field remains light at the end of inflation it is found that it can generate substantial statistical anisotropy in the spectrum and bispectrum of the curvature perturbation. In this case the non-Gaussianity in the curvature perturbation is predominantly anisotropic, which will be a testable prediction in the near future. If, on the other hand, the vector field is heavy at the end of inflation then it is demonstrated that particle production is approximately isotropic and the vector field alone can give rise to the curvature perturbation, without directly involving any fundamental scalar field. The parameter space for both possibilities is shown to be substantial. Finally, toy models are presented which show that the desired variation of the mass and kinetic function of the vector field can be realistically obtained, without unnatural tunings, in the context of supergravity or superstrings.

We analyze the Tevatron and Large Hadron Collider (LHC) reach for the Higgs sector of the minimal supersymmetric standard model (MSSM) in the presence of explicit $CP$ violation. Using the most recent studies from the Tevatron and LHC collaborations, we examine the CPX benchmark scenario for a range of $CP$-violating phases in the soft trilinear and gluino mass terms and compute the exclusion/discovery potentials for each collider on the $(M_{H^{+}},\tan \beta )$ plane. Projected results from standard model (SM)-like, nonstandard, and charged Higgs searches are combined to maximize the statistical significance. We exhibit complementarity between the SM-like Higgs searches at the LHC with low luminosity and the Tevatron, and estimate the combined reach of the two colliders in the early phase of LHC running.

We determine the parton distribution functions (PDFs) in a next-to-next-to-leading order QCD analysis of the inclusive neutral-current deep-inelastic-scattering (DIS) world data combined with the neutrino-nucleon DIS di-muon data and the fixed-target Drell-Yan data. The PDF evolution is performed in the $N_f=3$ fixed-flavor scheme and supplementary sets of PDFs in the 4- and 5-flavor schemes are derived from the results in the 3-flavor scheme using matching conditions. The charm-quark DIS contribution is calculated in a general-mass variable-flavor-number (GMVFN) scheme interpolating between the zero-mass 4-flavor scheme at asymptotically large values of momentum transfer $Q^2$ and the 3-flavor scheme prescription of Buza-Matiounine-Smith-van Neerven (BMSN) at the value of $Q^2=m_c^2$. The results in the general-mass variable-flavor-number scheme are compared with those of the fixed-flavor scheme and other prescriptions used in global fits of PDFs. The strong coupling constant is measured at an accuracy of $\approx 1.5\%$. We obtain at next-to-next-to-leading order ${\alpha }_s(M_Z^2)=0.1135\pm 0.0014$ in the fixed-flavor scheme and ${\alpha }_s(M_Z^2)=0.1129\pm 0.0014$ applying the Buza-Matiounine-Smith-van Neerven prescription. The implications for important standard candle and hard scattering processes at hadron colliders are illustrated. Predictions for cross sections of $W^{\pm }$- and $Z$-boson, the top-quark pair, and Higgs-boson production at the Tevatron and the LHC based on the 5-flavor PDFs of the present analysis are provided.

The strong decay properties of the newly observed states $D_{sJ}(3040)$, $D_{sJ}(2860)$, and $D_{sJ}(2710)$ are studied in a constituent quark model with quark-meson effective Lagrangians. We find that the $D_{sJ}(3040)$ could be identified as the low-mass physical state $|2P_1{⟩}_L$ ($J^P=1^{+}$) from the $D_s(2{}^{1}P_1)\mathrm{\text{−}}{D}_s(2{}^{3}P_1)$ mixing. The $D_{sJ}(2710)$ is likely to be the low-mass mixed state $|(SD){⟩}_L$ via the $1{}^{3}D_1\mathrm{\text{−}}2{}^{3}S_1$ mixing. In our model, the $D_{sJ}(2860)$ cannot be assigned to any single state with a narrow width and compatible partial widths to $DK$ and $D^{*}K$. Thus, we investigate a two-state scenario as proposed in the literature. In our model, one resonance is likely to be the $1{}^{3}D_3$ ($J^P=3^{-}$), which mainly decays into $DK$. The other resonance seems to be the $|1D_2{}^{\prime }{⟩}_H$, i.e. the high-mass state in the $1{}^{1}D_2\mathrm{\text{−}}1{}^{3}D_2$ mixing with $J^P=2^{-}$, of which the $D^{*}K$ channel is its key decay mode. We also discuss implications arising from these assignments and give predictions for their partner states such as $|(SD{)}^{\prime }{⟩}_H$, $|2P_1^{\prime }{⟩}_H$, $2{}^{3}P_0$, and $2{}^{3}P_2$, which could be helpful for the search for these new states in future experiments.

The production of single photons in low energy ($\sim 1\mathrm{GeV}$) neutrino scattering off nucleons is analyzed in the standard model. At very low energies, $E_{\nu }\ll \mathrm{GeV}$, a simple description of the chiral Lagrangian involving baryons and arbitrary $SU(2{)}_L\times U(1{)}_Y$ gauge fields is developed. Extrapolation of the process into the $\sim 1–2\mathrm{GeV}$ region is treated in a simple phenomenological model. Coherent enhancements in compound nuclei are studied. The relevance of single-photon events as a background to experimental searches for ${\nu }_{\mu }\to {\nu }_e$ is discussed. In particular, single photons are a plausible explanation for excess events observed by the MiniBooNE experiment.

We present an analytical derivation of the winding number counting topological defects created by an $O(N)$ symmetry-breaking quantum quench in $N$ spatial dimensions. Our approach is universal in the sense that we do not employ any approximations apart from the large-$N$ limit. The final result is nonperturbative in $N$, i.e., it cannot be obtained by an expansion in $1/N$, and we obtain far less topological defects than quasiparticle excitations, in sharp distinction to previous, low-dimensional investigations.

We consider brane gas models based on type II string theories and analyze the mass, the Ramond-Ramond charge, and the charge on moduli fluctuations of branes wrapping over cycles of a compactified space in the four-dimensional Einstein frame. A six-dimensional torus and Calabi-Yau threefolds are considered for the Kaluza-Klein reduction. A large volume of the compactified space and a weak string coupling gives rise to point particles of the wrapped branes which have a light mass and a small charge of the Ramond-Ramond flux and of the moduli fluctuations, while the particles become very heavy in the string frame. We find that the masses and the charges satisfy the seesaw like dual relations which become time independent in the four-dimensional Einstein frame.

We investigate the consequences of Birkhoff’s theorem in general relativity (GR) and in modified Newtonian dynamics (MOND). We study, in particular, the system of a finite-mass test particle inside a spherical shell. In both GR and MOND, we find nonvanishing acceleration for that test particle. The direction of the acceleration is such that it pushes the test particle toward the center of the shell. In GR, the acceleration is found analytically in the case of a small test mass with a small displacement from the center of the shell. In MOND, the acceleration is found analytically in the limit of large test mass and small displacement, and a comparison to numerical values is made. Numerical simulations are done for more general cases with parameters that mimic the system of a galaxy in a cluster. In GR, the acceleration is highly suppressed and physically insignificant. In MOND, on the contrary, the acceleration of the point particle can be a significant fraction of the field just outside of the spherical shell.

The cosmological primordial power spectrum is known to be one of the most promising observable to probe quantum gravity effects. In this article, we investigate how the tensor power spectrum is modified by loop-quantum-gravity corrections. The two most important quantum terms, holonomy and inverse volume, are explicitly taken into account in a unified framework. The equation of propagation of gravitational waves is derived and solved for one set of parameters.

We calculate the trispectrum $T_{\zeta }$ of the primordial curvature perturbation $\zeta$, generated during a slow-roll inflationary epoch by considering a two-field quadratic model of inflation with canonical kinetic terms. We consider loop contributions as well as tree-level terms, and show that it is possible to attain very high, including observable, values for the level of non-Gaussianity ${\tau }_{\mathrm{NL}}$ if $T_{\zeta }$ is dominated by the one-loop contribution. Special attention is paid to the claim in J. Cosmol. Astropart. Phys. 02 (2009) 017 that, in the model studied in this paper and for the specific inflationary trajectory we choose, the quantum fluctuations of the fields overwhelm the classical evolution. We argue that such a claim actually does not apply to our model, although more research is needed in order to understand the role of quantum diffusion. We also consider the probability that an observer in an ensemble of realizations of the density field sees a non-Gaussian distribution. In that respect, we show that the probability associated to the chosen inflationary trajectory is non-negligible. Finally, the levels of non-Gaussianity $f_{\mathrm{NL}}$ and ${\tau }_{\mathrm{NL}}$ in the bispectrum $B_{\zeta }$ and trispectrum $T_{\zeta }$ of $\zeta$, respectively, are also studied for the case in which $\zeta$ is not generated during inflation.

Annihilating dark matter (DM) models based on a scalar hidden sector with Higgs portal-like couplings to the standard model are considered as a possible explanation for recently observed cosmic-ray excesses. Two versions of the model are studied, one with nonthermal DM as the origin of the boost factor and one with Sommerfeld enhancement. In the case of nonthermal DM, four hidden sector scalars which transform under a $U(1{)}_X$ symmetry are added. The heaviest scalars decouple and later decay to DM scalars, thus providing the boost factor necessary to explain the present DM annihilation rate. The mass of the annihilating scalars is limited to $\lesssim 600\mathrm{GeV}$ for the model to remain perturbative. $U(1{)}_X$ breaking to $Z_2$ at the electroweak transition mixes light O(100) MeV hidden sector scalars with the Higgs. The DM scalars annihilate to these light scalars, which subsequently decay to two ${\mu }^{+}{\mu }^{-}$ pairs via Higgs mixing, thus generating a positron excess without antiprotons. Decay to ${\mu }^{+}{\mu }^{-}$ rather than $e^{+}{e}^{-}$ is necessary to ensure a fast enough light scalar decay rate to evade light scalar domination at nucleosynthesis. In the version with Sommerfeld enhancement only three new scalars are necessary. TeV scale DM masses can be accommodated, allowing both the higher energy electron plus positron excess and the lower energy positron excess to be explained. DM annihilates to $2{\mu }^{+}{\mu }^{-}$ pairs as in the nonthermal model. This annihilation mode may be favored by recent observations of the electron plus positron excess by FERMI and HESS.

The stable configurations of nonrotating and rotating hybrid stars composed of color-superconducting quark matter cores are constructed using several equations of state (EOSs). We use a set of diverse EOSs for the nuclear matter which represents the low density phase. The EOSs at higher densities correspond to the quark matter in the color-superconducting phase and are computed within the Nambu-Jona-Lasinio-like model for different values of the scalar diquark and vector current couplings strengths. The phase transition to the quark matter is computed by a Maxwell construction. We find that the stability of the hybrid stars are mainly governed by the behavior of the EOSs for the color-superconducting quark matter. However the compositions of hybrid stars are sensitive to the EOS of the nuclear matter. The value of the critical rotation frequency for the hybrid star depends strongly on the EOS of the nuclear matter as well as that for the color-superconducting quark matter. Our results indicate that the EOS for the color-superconducting quark matter can be obtained, by adjusting the parameters of the Nambu-Jona-Lasinio model, to yield the stable configurations of the hybrid star having the maximum mass $\sim 1.5M_{\odot }$ in the nonrotating limit and the critical rotation frequency $\sim 1\mathrm{kHz}$.

In this work we discuss the interest of measuring the ratio of $p\overline{p}$ annihilation into kaon and pion pairs near the threshold region, where the $S$ state dominates. It is shown that a good agreement with existing data on the ratio of the yields of charged kaon to pion pairs is obtained taking into account not only quark rearrangement in the incident hadrons, but also vacuum excitations.

The bounds and presence of manifest right-handed currents in neutron beta decay are reviewed. Assuming the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, the current experimental situation imposes very stringent limits on the mixing angle, $-0.00077<\zeta <0.00089$, and on the mass eigenstate, $M_2(\mathrm{GeV})\in (291.4,439.9)$, in contradiction with the established lower bound on $M_2$.

We perform an analytical study of the scattering matrix and bound states in problems with many physical coupled channels. We establish the relationship of the couplings of the states to the different channels, obtained from the residues of the scattering matrix at the poles, with the wave functions for the different channels. The couplings basically reflect the value of the wave functions around the origin in coordinate space. In the concrete case of the $X(3872)$ resonance, understood as a bound state of $D^0{\overline{D}}^{*0}$ and $D^{+}{D}^{*-}$ (and $c.c.$ From now on, when we refer to $D^0{\overline{D}}^{*0}$ , $D^{+}{D}^{*-}$, or $D{\overline{D}}^{*}$ we are actually referring to the combination of these states with their complex conjugate in order to form a state with positive C-parity), with the $D^0{\overline{D}}^{*0}$ loosely bound, we find that the couplings to the two channels are essentially equal leading to a state of good isospin $I=0$ character. This is in spite of having a probability for finding the $D^0{\overline{D}}^{*0}$ state much larger than for $D^{+}{D}^{*-}$ since the loosely bound channel extends further in space. The analytical results, obtained with exact solutions of the Schrödinger equation for the wave functions, can be useful in general to interpret results found numerically in the study of problems with unitary coupled channels methods.

We present a detailed analysis of ${\rho }^0$ electroproduction at intermediate energy for quasielastic knockout kinematics. The approach is based on an effective Lagrangian which generates exchanges of scalar, pseudoscalar, axial-vector, and tensor mesons. The specific role of mesons with different values for $J^{PC}$ is analyzed. We show that the ${\pi }^0$ exchange amplitude and its interference terms with $\eta ({\eta }^{\prime })$ and $f_1$ exchanges dominate in the transverse part of the cross section ${\sigma }_T$. The main role plays the ${\pi }^0\to {\rho }^0$ M1 spin transition when coupling the virtual photons to the nucleon. In contrast, the longitudinal cross section ${\sigma }_L$ is generated by a series of scalar meson exchanges. To extract the dominant term, more detailed information on the inner structure of scalar mesons is required. It turns out that recent data of the CLAS Collaboration on ${\sigma }_L$ and ${\sigma }_T$ can be described with reasonable accuracy if one proposes the quarkonium structure for the heavy scalar mesons ($M\gtrsim 1.3\mathrm{GeV}$). On this basis the differential cross sections $d{\sigma }_L/dt$ and $d{\sigma }_T/dt$ are calculated and compared with the latest CLAS data.