118137426
On Deformations of Generalized Complex Structures: the Generalized Calabi-Yau Case
We prove an analog of the Tian-Todorov theorem for twisted generalized Calabi-Yau manifolds; namely, we show that the moduli space of generalized complex structures on a compact twisted generalized Calabi-Yau manifold is unobstructed and smooth. We also construct the extended moduli space and study its Frobenius structure. The physical implications are also discussed.
120831466
Noncoplanarity effects in proton-proton bremsstrahlung
Noncoplanarity in proton-proton bremsstrahlung is investigated. Significant effects are observed for certain photon polar angles, psi(gamma). Such noncoplanarity effects, not of dynamical origin, are possibly responsible for past disagreements between theory and experiment. The Harvard noncoplanar coordinate system, which avoids kinematic singularities in the cross section, is used in our calculations and is recommended for use in the analysis of experimental data. Alternative methods of presenting cross sections are discussed. [S0556-2813(98)50110-0].
123491963
Noncoplanarity in proton-proton bremsstrahlung
Using the soft-photon approximation, we address the issue of the importance of noncoplanarity effects in proton-proton bremsstrahlung, We investigate the noncoplanar cross section as a function of the noncoplanarity angle (φ) over bar for the entire range of the photon polar angle psi(gamma). The (φ) over bar dependence is shown to provide a significant variation in the cross section, for a given psi(gamma). Thus, there can be some uncertainty in determining experimental coplanar cross sections. To avoid the phase-space singularities of spherical geometry. we utilize the Harvard noncoplanar geometry. A detailed explication of the Harvard geometry is provided, Comparison of our calculations with experimental data is included.
121496385
Meson exchange currents in neutron-proton bremsstrahlung
Background: The meson exchange current (MEC) contribution is important in the neutron-proton bremsstrahlung process (np gamma) when the two nucleon-scattering angles are small. However, our understanding of such effects is limited, and the reason why meson exchange current effects dominate the np gamma cross section has not been thoroughly investigated. Purpose: The primary focus of this investigation is to understand the origin of the MEC contribution, to identify the leading MEC amplitudes, and to comprehend why these MEC amplitudes dominate the np gamma cross sections. Method: We used a new method that combines the one-boson-exchange (OBE) approach with the soft-photon approach to define 10 different np gamma amplitudes. These amplitudes are used to calculate np gamma cross sections at 225 MeV for nucleon laboratory scattering angles lying between 12(degrees) and 43(degrees). The results of these calculations are then compared to investigate the meson exchange current effect in np gamma. Results: (i) The OBE amplitude M(np gamma,mu)(PS) and the two-u-two-t special (TuTts) soft-photon amplitude M(np gamma,mu)(TuTts) predict quantitatively similar np gamma cross sections. (ii) The MEC effect is found to be significant when the two nucleon-scattering angles are far from the elastic limit (45(degrees)), but the effect is insignificant when the nucleon angles approach the elastic limit. (iii) The origin of the MEC effect and the leading MEC amplitudes have been identified in this investigation. Furthermore, the reason is now clear why the leading MEC amplitudes dominate the np gamma cross section when the nucleon-scattering angles are small. (iv) The contribution from the anomalous magnetic moments of the proton and the neutron is confirmed to be negligibly small. (v) In general, the theoretical cross sections using the amplitude M(np gamma,mu)(PS), or the amplitude M(np gamma,mu)(TuTts), are consistent with the triple differential cross sections recently measured at the Los Alamos National Laboratory. However, there exists an unexplained discrepancy between theory and experiment in some cases. Conclusions: The findings of this investigation have enhanced our understanding of the meson exchange current effect in np gamma. The comparative amplitude method introduced can be used for other bremsstrahlung investigations.
13345134
D-branes in topological minimal models: the Landau–Ginzburg approach
We study D-branes in topologically twisted N = 2 minimal models using the Landau-Ginzburg realization. In the cases of A and D-type minimal models we provide what we believe is an exhaustive list of topological branes and compute the corresponding boundary OPE algebras as well as all disk correlators. We also construct examples of topological branes in E-type minimal models. We compare our results with the boundary state formalism, where possible, and find agreement.
18559665
Topological sigma-models with H-flux and twisted generalized complex manifolds
We study the topological sector of N = 2 sigma-models with HH-flux. It has been known for a long time that the target-space geometry of these theories is not Kahler and can be described in terms of a pair of complex structures, which do not commute, in general, and are parallel with respect to two different connections with torsion. Recently an alternative description of this geometry was found, which involves a pair of commuting twisted generalized complex structures on the target space. In this paper, we define and study the analogs of A and B-models for N = 2 sigma-models with HH-flux and show that the results are naturally expressed in the language of twisted generalized complex geometry. For example, the space of topological observables is given by the cohomology of a Lie algebroid associated to one of the two twisted generalized complex structures. We determine the topological scalar product, which endows the algebra of observables with the structure of a Frobenius algebra. We also discuss mirror symmetry for twisted generalized Calabi-Yau manifolds.
119183402
Exploring the full parameter space for an interacting dark energy model with recent observations including redshift-space distortions: Application of the parametrized post-Friedmann approach
Dark energy can modify the dynamics of dark matter if there exists a direct interaction between them. Thus a measurement of the structure growth, e.g., redshift-space distortions (RSD), can provide a powerful tool to constrain the interacting dark energy (IDE) models. For the widely studied $Q=3\beta H\rho_{de}$ model, previous works showed that only a very small coupling ($\beta\sim\mathcal{O}(10^{-3})$) can survive in current RSD data. However, all these analyses had to assume $w>-1$ and $\beta>0$ due to the existence of the large-scale instability in the IDE scenario. In our recent work [Phys. Rev. D 90, 063005 (2014)], we successfully solved this large-scale instability problem by establishing a parametrized post-Friedmann (PPF) framework for the IDE scenario. So we, for the first time, have the ability to explore the full parameter space of the IDE models. In this work, we reexamine the observational constraints on the $Q=3\beta H\rho_{de}$ model within the PPF framework. By using the Planck data, the baryon acoustic oscillation data, the JLA sample of supernovae, and the Hubble constant measurement, we get $\beta=-0.010^{+0.037}_{-0.033}$ ($1\sigma$). The fit result becomes $\beta=-0.0148^{+0.0100}_{-0.0089}$ ($1\sigma$) once we further incorporate the RSD data in the analysis. The error of $\beta$ is substantially reduced with the help of the RSD data. Compared with the previous results, our results show that a negative $\beta$ is favored by current observations, and a relatively larger interaction rate is permitted by current RSD data.
118606894
Possible capture of keV sterile neutrino dark matter on radioactive beta-decaying nuclei
There exists an observed "desert" spanning six orders of magnitude between O(0.5) eV and O(0.5) MeV in the fermion mass spectrum. We argue that it might accommodate one or more keV sterile neutrinos as a natural candidate for warm dark matter. To illustrate this point of view, we simply assume that there is one key sterile neutrino nu(4) and its flavor eigenstate nu(s) weakly mixes with three active neutrinos. We clarify different active-sterile neutrino mixing factors for the radiative decay of nu(4) and beta decays in a self-consistent parametrization. A direct detection of this keV sterile neutrino dark matter in the laboratory is in principle possible since the nu(4) component of nu(e) can leave a distinct imprint on the electron energy spectrum when it is captured on radioactive beta-decaying nuclei. We carry out an analysis of its signatures in the capture reactions nu(e) + H-3 -> He-3 + e(-) and nu(e) + Ru-106 -> Rh-106 + e(-) against the beta-decay backgrounds, and conclude that this experimental approach might not be hopeless in the long run. (C) 2010 Elsevier B.V. All rights reserved.
56284746
Pragmatic view of short-baseline neutrino oscillations
We present the results of global analyses of short-baseline neutrino oscillation data in 3 + 1, 3 + 2 and 3 + 1 + 1 neutrino mixing schemes. We show that the data do not allow us to abandon the simplest 3 + 1 scheme in favor of the more complex 3 + 2 and 3 + 1 + 1 schemes. We present the allowed region in the 3 + 1 parameter space, which is located at Delta m(41)(2) between 0.82 and 2.19 eV(2) at 3 sigma. The case of no oscillations is disfavored by about 6 sigma, which decreases dramatically to about 2 sigma if the Liquid Scintillating Neutrino Detector (LSND) data are not considered. Hence, new high-precision experiments are needed to check the LSND signal.
123193403
The rate of the sphaleron transition in the (1 + 1)-dimensional Abelian Higgs model on a circle
Abstract The rate of fermion number non-conservation at finite temperatures is discussed in the (1 + 1)-dimensional Abelian Higgs model on a circle. An effective potential is used to estimate the one-loop correction to the effective action remaining after the treatment of zero modes. With this method it is not necessary to know all the normal modes of the sphaleron. The expression of the rate is given for the case of M W ⪡ M H .
119209195
Generalized Froggatt–Nielsen mechanism
We propose a Generalized Froggatt–Nielsen mechanism in which the GUT gauge symmetry breaking and the generation of hierarchical flavor structure have the same origin. Assuming universality conditions for coefficients corresponding to different contractions, we can get the realistic standard model mass hierarchy and mixings in SU(5) GUT model as well as in SO(10) GUT model in several ways. With very free parameters, the Generalized Froggatt–Nielsen mechanism is very predictive and it can be very useful in GUT model building as well as in solving the flavor puzzle in standard model.