119235960
Note on Non-Gaussianities in Two-field Inflation
Two-field slow-roll inflation is the most conservative modification of a single-field model. The main motivations to study it are its entropic mode and non-Gaussianity. Several years ago, for a two-field model with additive separable potentials, Vemizzi and Wands invented an analytic method to estimate its non-Gaussianities. Later on, Choi et al. applied this method to the model with multiplicative separable potentials. In this note, we design a larger class of models whose non-Gaussianity can be estimated by the same method. Under some simplistic assumptions, roughly these models are unlikely able to generate a large non-Gaussianity. We look over some specific models of this class by scanning the full parameter space, but still no large non-Gaussianity appears in the slow-roll region. These models and scanning techniques would be useful for a future model hunt if observational evidence shows up for two-field inflation.
119250105
M2-branes coupled to antisymmetric fluxes
By turning on antisymmetric background fluxes, we study how multiple M2-branes are coupled to them. Our investigation concentrates on the gauge invariance conditions for the Myers-Chern-Simons action. Furthermore, the dimensional reduction of M2-branes to D2-branes introduces more constraints on the newly introduced tensors. Particularly, for the theory based on A(4) algebra, we are able to fix all components of them up to an overall normalization constant. These results can not be simply obtained from the previously proposed cubic matrix representation for this algebra. We also comment on cubic matrices as the representations of 3-algebras.
118153543
An oblique membrane paradigm for cosmological horizon
The membrane paradigm is a formalism for studying the event horizon of black holes. After analyzing it with some technical details and realizing it in the Reissner-Nordstrom black hole, we extend the paradigm to cosmological horizons. A standard membrane paradigm is established for the pure de Sitter horizon, and an oblique membrane paradigm is proposed for the trapping horizon of the Friedmann-Lemaitre-Robertson-Walker universe. In the latter case, the cosmological stretched horizon is oblique, thus the running of renormalization parameter is nonzero in the timelike direction and gives a correction to the membrane pressure. In this paradigm, the cosmological equations come from continuity equations of the membrane fluid and the bulk fluid respectively.
119201058
Cosmic steps in modeling dark energy
Past and recent data analyses gave some hints of steps in dark energy. Considering dark energy as a dynamical scalar field, we investigate several models with various steps: a step in the scalar potential, a step in the kinetic term, a step in the energy density, and a step in the equation-of-state parameter $w$. These toy models provide a workable mechanism to generate steps and features of dark energy. Remarkably, a single real scalar can cross $w=\ensuremath{-}1$ dynamically with a step in the kinetic term.
16941003
From N M2's to N D2's
In this short note, we reduce the N=6, U(N)xU(N) Chern-Simons gauge theories to N=8, U(N) Yang-Mills gauge theories. This process corresponds to recovering the world-volume theory of N D2-branes from that of N M2-branes in an intermediate energy range. The supersymmetries are enhanced because in this limit the branes localize far away from the orbifold singularity. Our main scheme is exactly in accordance with Mukhi and Papageorgakis's earlier work, although the Higgs mechanism becomes trickier in the present case. We also speculate on applying the scheme to a large class of new Bagger-Lambert models more generally.
118390460
1/R correction to gravity in the early universe
To explain the accelerated expansion of the late universe, the 1/R correction to Einstein gravity is usually considered, where R is the Ricci scalar. This correction term, if stable, is generally believed to be negligible during inflation. However, if the 1/R term is inflaton dependent, it will dramatically change the story of inflation. The entropy perturbation will naturally appear and drive the evolution of curvature perturbation outside the Hubble horizon. In a large class of models, the entropy perturbation can be made nearly scale invariant. In Einstein gravity the single-field inflation with a quartic potential has been ruled out by recent observations, but it revives when the 1/R term is turned on. The evolution of non-Gaussianities on a large scale are also studied and applied to inflation with 1/R correction. In some specific models, a large non-Gaussianity can be naturally generated outside the horizon. A recent study ruled out almost all f(R) models during the matter-dominated phase. Taking this into consideration, we are left with a limited class of model which recovers the Einstein gravity soon after reheating.
122356377
The use of the discriminant analysis method for e π μ separation in BES
Abstract We use the discriminant analysis method in multivariate statistical theory to handle the e π μ separation in BES, describing the principle of the discriminant analysis method, deriving the unstandardized discriminant functions (responsible for particle separation), giving the discriminant efficiency for e π μ and comparing the results from the discriminant analysis method with those obtained in a conventional way.
119300428
Why X(3915) is so narrow as a $\chi_{c0}(2P)$ state
New resonance X(3915) was identified as the charmonium $\chi_{c0}(2P)$ by BABAR Collaboration, but there seems still open question of this assignment: why its full width is so narrow? To answer this question, we calculate the Okubo-Zweig-Iizuka (OZI) allowed strong decays $X(3915)\to D \bar D$, where X(3915) is assigned as a $\chi_{c0}(2P)$ state, and estimate its full width in the cooperating framework of $^3/!P_0^{}$ model and the Bethe-Salpeter (BS) method using the Mandelstam Formalism, during which non-perturbative QCD effects of the hadronic matrix elements are well considered by overlapping integral over the relativistic Salpeter wave functions of the initial and finial states. We find the node structure of $\chi_{c0}(2P)$ wave function resulting in the narrow width of X(3915) and show the dependence of the decay width on the variation of the initial mass of X(3915). We point out that the rate of $\frac{\Gamma(X(3915)\to D^+ D^-)}{\Gamma(X(3915)\to D^0 \bar D^0)}$ is crucial to confirm whether X(3915) is the $\chi_{c0}(2P)$ state or not.
118507158
Selection and Mid-infrared Spectroscopy of Ultraluminous Star-forming Galaxies at z ~ 2
Starting from a sample of 24 ?m sources in the Extended Groth Strip, we use 3.6-8 ?m color criteria to select ultraluminous infrared galaxies (ULIRGs) at z ~ 2. Spectroscopy from 20-38 ?m of 14 objects verifies their nature and gives their redshifts. Multi-wavelength data for these objects imply stellar masses >1011 M ? and star formation rates ?410 M ? yr?1. Four objects of this sample observed at 1.6 ?m (rest-frame visible) with Hubble Space Telescope/WFC3 show diverse morphologies, suggesting that multiple formation processes create ULIRGs. Of the 14 objects, 4 show signs of active galactic nuclei, but the luminosity appears to be dominated by star formation in all cases.
123145784
OZI-ALLOWED TWO BODY ϒ DECAYS IN THE 3P0 MODEL WITH THE RELATIVISTIC WAVE FUNCTIONS
We combine the Bethe–Salpeter method with the 3P0 model to describe OZI-allowed two body meson decays. In this combined method, the relativistic wave functions defined in the Salpeter equation show up in the decay amplitude of the 3P0 model automatically. We apply the method to OZI-allowed ϒ(4S, 5S, 6S) two body decays. The results are roughly consistent with the experimental data and the predictions of ϒ(6S) decays are given.
119181798
Radiative E1 decays of X(3872)
Abstract Radiative E1 decay widths of X ( 3872 ) are calculated through the relativistic Salpeter method, with the assumption that X ( 3872 ) is the χ c 1 ( 2 P ) state, which is the radial excited state of χ c 1 ( 1 P ) . We first calculated the E1 decay width of χ c 1 ( 1 P ) . The result is in agreement with experimental data excellently. Then we calculated the width of X ( 3872 ) with the assignment χ c 1 ( 2 P ) . Results are: Γ ( X ( 3872 ) → γ J / ψ ) = 33.0 keV , Γ ( X ( 3872 ) → γ ψ ( 2 S ) ) = 146 keV and Γ ( X ( 3872 ) → γ ψ ( 3770 ) ) = 7.09 keV . The ratio Br ( X ( 3872 ) → γ ψ ( 2 S ) ) / Br ( X ( 3872 ) → γ J / ψ ) = 4.4 agrees with experimental data by BaBar, but is larger than the new up-bound reported by Belle recently. With the same method, we also predicted the decay widths, Γ ( χ b 1 ( 1 P ) ) → γ ϒ ( 1 S ) = 30.0 keV , Γ ( χ b 1 ( 2 P ) ) → γ ϒ ( 1 S ) = 5.65 keV and Γ ( χ b 1 ( 2 P ) ) → γ ϒ ( 2 S ) = 15.8 keV , from which we get the full widths: Γ ( χ b 1 ( 1 P ) ) ∼ 85.7 keV and Γ ( χ b 1 ( 2 P ) ) ∼ 66.5 keV .