We point out that the electric dipole moment of the neutron in the standard model is generated already at tree level to the second order in the weak interactions due to bound-state effects, without short-distance penguin loops. The related contribution has a regular nonvanishing chiral limit and does not depend on the mass splitting between $s$ and $d$ quarks. We estimate it to be roughly ${10}^{-31}e·\mathrm{cm}$ and expect a more accurate evaluation in the future. We comment on the connection between $d_n$ and the direct $CP$ violation in $D$ decays.

We study phenomenological aspects of the minimal SUSY standard model with extra U(1) gauge symmetry. We find that the lightest Higgs boson mass can be increased up to 125 GeV without introducing a large SUSY scale or large $A$-terms, in the frameworks of the CMSSM and gauge-mediated SUSY-breaking models. This scenario can simultaneously explain the discrepancy of the muon anomalous magnetic moment (muon $g-2$) at the $1\sigma$ level in both of the frameworks, U(1)-extended CMSSM/GMSB models. In the CMSSM case, the dark matter abundance can also be explained.

Quantum interference of helicity amplitudes provides a powerful tool for measuring the spins of new particles. By looking at the azimuthal angular dependence of the differential cross section in the production followed by decay of a new particle species, one can determine its spin by looking at the various cosine modes. The heavy spin-2 Kaluza-Klein graviton provides a unique signature with a $\cos (4\varphi )$ mode. We study the feasibility of this approach to measuring the spin of the Kaluza-Klein graviton in the Randall-Sundrum model at the LHC.

We assume that the most important quark correlations are pairwise at all baryon densities. We introduce correlated pairs by means of Bogoliubov transformations which are functions of time and spatial gauge fields, in the formalism of the transfer matrix with lattice regularization. The dependence on time and gauge fields allows us to enforce gauge invariance and other symmetries in the transformed quantities in the same way as in the original ones. We derive the quark contribution to the free energy at finite chemical potential in a certain approximation. Its expression cannot be evaluated analytically, but it has a definite sign.

With the one-boson-exchange model, we study the interaction between the $S$-wave $D^{(*)}/D_s^{(*)}$ meson and S-wave $B^{(*)}/B_s^{(*)}$ meson considering the S-D mixing effect. Our calculation indicates that there may exist the $B_c$-like molecular states. We estimate their masses and list the possible decay modes of these $B_c$-like molecular states, which may be useful to the future experimental search.

Most models for soft interactions which were proposed prior to the measurements at the LHC, are only marginally compatible with LHC data, the Gotsma-Levin-Maor model has the same deficiency. In this paper we investigate possible causes of the problem, by considering separate fits to the high energy ($W>500\mathrm{GeV}$), and low energy ($W<500\mathrm{GeV}$) data. Our new results are moderately higher than our previous predictions. Our results for total and elastic cross sections are systematically lower that the recent Totem and Alice published values, while our results for the inelastic and forward slope agree with the data. If with additional experimental data, the errors are reduced, while the central cross section values remain unchanged, we will need to reconsider the physics on which our model is built.

We study the $N\Delta \gamma$ transition in the Dyson-Schwinger approach. The nucleon and $\Delta$ baryons are treated as quark-diquark bound states, where the ingredients of the electromagnetic transition current are computed self-consistently from the underlying dynamics in QCD. Although our approach does not include pion-cloud effects, we find that the electric and Coulomb quadrupole form-factor ratios $R_{\mathrm{EM}}$ and $R_{\mathrm{SM}}$ show good agreement with experimental data. This implies that the deformation from a spherical charge distribution inside both baryons can be traced back to the appearance of $p$ waves in the nucleon and $\Delta$ bound-state amplitudes which are a consequence of Poincaré covariance. On the other hand, the dominant transition amplitude, i.e. the magnetic dipole transition form factor, underestimates the data by $\sim 25\%$ in the static limit whereas agreement is achieved at larger momentum transfer, which is consistent with missing pion-cloud contributions. We furthermore find that the static properties of the form factors are not very sensitive to a variation of the current-quark mass.

The ARGO-YBJ experiment detects extensive air showers in a wide energy range by means of a full-coverage detector which is in stable data taking in its full configuration since November 2007 at the YBJ International Cosmic Ray Observatory (4300 m a.s.l., Tibet, People’s Republic of China). In this paper the measurement of the light-component spectrum of primary cosmic rays in the energy region $(5÷200)\mathrm{TeV}$ is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.

We report on charmonium measurements [$J/\psi$ (1S), ${\psi }^{\prime }$ (2S), and ${\chi }_c$ (1P)] in $p+p$ collisions at $\sqrt{s}=200\mathrm{GeV}$. We find that the fraction of $J/\psi$ coming from the feed-down decay of ${\psi }^{\prime }$ and ${\chi }_c$ in the midrapidity region ($|y|<0.35$) is $9.6\pm 2.4\%$ and $32\pm 9\%$, respectively. We also present the $p_T$ and rapidity dependencies of the $J/\psi$ yield measured via dielectron decay at midrapidity ($|y|<0.35$) and via dimuon decay at forward rapidity ($1.2<|y|<2.2$). The statistical precision greatly exceeds that reported in our previous publication [Phys. Rev. Lett. 98, 232002 (2007)]. The new results are compared with other experiments and discussed in the context of current charmonium production models.

We consider tachyon condensation between a D-brane and an anti–D-brane in superstring theory, when they are separated in their common transverse directions. A simple rolling tachyon solution, which describes the time evolution of the process, is studied from the point of view of boundary conformal field theory. By computing the boundary beta functions of the system, one finds that this theory is conformal and hence corresponds to an exact solution of the string theory equations of motion. By contrast, the time-reversal-symmetric rolling tachyon is not conformal. These results put constraints on the space-time effective actions for the system.

Inspired by the method of null-dimensional reduction and by the holographic correspondence between Vasiliev’s higher-spin gravity and the critical $O(N)$ model, a bulk dual of the unitary and the ideal nonrelativistic Fermi gases is proposed.

We investigate the effects of higher-order curvature corrections to Einstein’s gravity on the critical phenomenon near the black hole threshold, namely, the Choptuik phenomenon. We simulate numerically a five-dimensional spherically symmetric gravitational collapse of massless scalar field in Einstein-Gauss-Bonnet gravity towards a black hole formation threshold. When the curvature is sufficiently large, the additional higher-order terms affect the evolution of the whole system. Since high curvature characterizes the region when the critical behavior takes place, this critical behavior is destroyed. Both the self-similarity and the mass scaling relation disappear. Instead we find a different behavior near the black hole threshold, which depends on the coupling constant of the higher-order terms. The new features include a change of the sign of the Ricci scalar on the origin which indicates changes in the local geometry of spacetime, and never occurs in classical general relativity collapse, and oscillations with a constant rather than with a diminishing length scale.

We examine here the acceleration of particles and high-energy collisions in the Janis-Newman-Winicour (JNW) spacetime, which is an extension of the Schwarzschild geometry when a massless scalar field is included. We show that while the center of mass energy of collisions of particles near the event horizon of a black hole is not significantly larger than the rest mass of the interacting particles, in an analogous situation, it could be arbitrarily large in the JNW spacetime near the naked singularity. The high-energy collisions are seen to be generic in the presence of a photon sphere in the JNW spacetime, whereas an extreme fine-tuning of the angular momentum of the colliding particles is required when the photon sphere is absent. The center of mass energy of collision near the singularity grows slowly for small and extremely large deviations from the Schwarzschild black hole, but for intermediate strengths of the scalar field it rises moderately fast. As a possible and potentially interesting application, we point out that the presence of such high-energy collisions may help the black hole configurations to be distinguished from a naked singularity.

In Ashtekar’s Hamiltonian formulation of general relativity, and in loop quantum gravity, Lorentz covariance is a subtle issue that has been strongly debated. Maintaining manifest Lorentz covariance seems to require introducing either complex-valued fields, presenting a significant obstacle to quantization, or additional (usually second class) constraints whose solution renders the resulting phase space variables harder to interpret in a spacetime picture. After reviewing the sources of difficulty, we present a Lorentz covariant, real formulation in which second class constraints never arise. Rather than a foliation of spacetime, we use a gauge field $y$, interpreted as a field of observers, to break the SO(3, 1) symmetry down to a subgroup $\mathrm{SO}(3{)}_y$. This symmetry breaking plays a role analogous to that in MacDowell-Mansouri gravity, which is based on Cartan geometry, leading us to a picture of gravity as “Cartan geometrodynamics.” We study both Lorentz gauge transformations and transformations of the observer field to show that the apparent breaking of SO(3, 1) to SO(3) is not in conflict with Lorentz covariance.

A modified-gravity-type model of two hypothetical massless vector fields is presented. These vector fields are gravitationally coupled to standard matter and an effective cosmological constant. Considered in a cosmological context, the vector fields dynamically cancel an arbitrary cosmological constant, and flat Minkowski spacetime appears as the limit of attractor-type solutions of the field equations. Asymptotically, the field equations give rise to a standard Friedmann-Robertson-Walker universe and standard Newtonian gravitational dynamics of small systems.

We build on existing calculations of the wall velocity of the expanding bubbles of the broken symmetry phase in a first-order electroweak phase transition within the light stop scenario (LSS) of the MSSM. We carry out the analysis using the 2-loop thermal potential for values of the Higgs mass consistent with present experimental bounds. Our approach relies on describing the interaction between the bubble and the hot plasma by a single friction parameter, which we fix by matching to an existing 1-loop computation and extrapolate to our regime of interest. For a sufficiently strong phase transition (in which washout of the newly created baryon asymmetry is prevented) we obtain values of the wall velocity, $v_w\approx 0.05$, far below the speed of sound in the medium, and not very much deviating from the previous 1-loop calculation. We find that the phase transition is about 10% stronger than suggested by simply evaluating the thermal potential at the critical temperature. We also comment on the relevance of our results to extended models, such as the NMSSM.

We reexamine the recently proposed “little inflation” scenario that allows for a strong first-order phase transition of QCD at non-negligible baryon number in the early Universe and its possible observable consequences. The scenario is based on the assumptions of a strong mechanism for baryogenesis and a quasistable QCD-medium state which triggers a short inflationary period of inflation diluting the baryon asymmetry to the value observed today. The cosmological implications are reexamined, namely, effects on primordial density fluctuations up to dark matter mass scales of $M_{\max }\sim 1M_{\odot }$, change in the spectral slope up to $M_{\max }\sim {10}^6{M}_{\odot }$, production of seeds for the present galactic and extragalactic magnetic fields, and a gravitational wave spectrum with a peak frequency around ${\nu }_{\mathrm{peak}}\sim 4\times {10}^{-8}\mathrm{Hz}$. We discuss the issue of nucleation in more detail and employ a chiral effective model of QCD to study the impact on small scale structure formation.

We compute the super-Hubble evolution of non-Gaussianity of primordial curvature perturbations in two-field inflation models by employing two formalisms: $\delta N$ and covariant formalisms. Although the two formalisms treat the evolution of fluctuations radically different, we show that the formulas of the $f_{\mathrm{NL}}$ parameter agree quantitatively with each other within 1% accuracy. We analytically find that the amplitude of $f_{\mathrm{NL}}$ decays no faster than $a^{-3}$ as the inflationary trajectory reaches to the adiabatic limit for generic potentials.

We study a regression characterization for the quadratic estimator of weak lensing, developed by Hu and Okamoto [W. Hu, Astrophys. J. 557, L79 (2001).][W. Hu and T. Okamoto, Astrophys. J. 574, 566 (2002).][T. Okamoto and W. Hu, Phys. Rev. D 67, 083002 (2003).], for cosmic microwave background observations. This characterization motivates a modification of the quadratic estimator by an adaptive Wiener filter which uses the robust Bayesian techniques described in [J. Berger, Ann. Stat. 8, 716 (1980).][J. Berger, Statistical Decision Theory and Bayesian Analysis (Springer, New York, 1980).][W. Strawderman, Ann. Stat. 42, 385 (1971).]. This technique requires the user to propose a fiducial model for the spectral density of the unknown lensing potential but the resulting estimator is developed to be robust to mis-specification of this model. The role of the fiducial spectral density is to give the estimator superior statistical performance in a “neighborhood of the fiducial model” while controlling the statistical errors when the fiducial spectral density is drastically wrong. Our estimate also highlights some advantages provided by a Bayesian analysis of the quadratic estimator.

Recently, the ATLAS and CMS collaborations reported exciting hints of the standard model-like Higgs boson with a mass around 125 GeV. A Higgs boson this heavy is difficult to realize in conventional models of gauge mediation. Here we revisit the lightest Higgs boson mass in “more generic gauge mediation,” where the Higgs doublets mix with the messenger doublets. We show that a Higgs boson mass around 125 GeV can be realized in more generic gauge mediation models, even for a relatively light gluino mass, $m_{\mathrm{gluino}}\sim 1\mathrm{TeV}$. We also show that the muon anomalous magnetic moment can be within $1\sigma$ of the experimental value for these models, even when the Higgs boson is relatively heavy. We also discuss the LHC constraints and the prospects of discovery.