115635245
Topological sigma models and generalized geometries
We study the relation between topological sigma models and generalized geometries. The existence conditions for the most general type of topological sigma models obtained from twisting the N=(2,2) supersymmetric sigma model are investigated, and are found to be related to twisted generalized Calabi-Yau structures. The properties of these topological sigma models are analyzed in detail. The observables are shown to be described by the cohomology of a Lie algebroid, which is intrinsically associated with the twisted generalized Calabi-Yau structure. The Frobenius structure on the space of states and the effects of instantons are analyzed. We also study D-branes in these topological sigma models, and demonstrate that they also admit descriptions in terms of generalized geometries.
7213382
Topological Correlators in Landau-Ginzburg Models with Boundaries
We compute topological correlators in Landau-Ginzburg models on a Riemann surface with arbitrary number of handles and boundaries. The boundaries may correspond to arbitrary topological D-branes of type B. We also allow arbitrary operator insertions on the boundary and in the bulk. The answer is given by an explicit formula which can be regarded as an open-string generalization of C. Vafa’s formula for closed-string topological correlators. We discuss how to extend our results to the case of Landau-Ginzburg orbifolds. e-print archive: http://lanl.arXiv.org/abs/hep-th/0305136
18450542
Comment on "Validity of certain soft photon amplitudes"
The criteria suggested by Welsh and Fearing to judge the validity of certain soft-photon amplitudes are examined. Some aspects of their analysis lead to incorrect conclusions. [copyright] [ital 1999] [ital The American Physical Society]
121260316
Proton-proton bremsstrahlung: Consequences of different on-shell-point conditions
Background: Proton-proton bremsstrahlung (pp{gamma}) is investigated both theoretically and experimentally. The pp{gamma} amplitudes can be classified according to the number and location of on-shell points at which they are evaluated. Quantitative understanding of the effect on the pp{gamma} cross section of using different on-shell-point conditions is lacking, but it is essential to identifying the photon emission mechanism governing the pp{gamma} process. Method: Four different pp{gamma} amplitudes, which include four-on-shell-point amplitudes and one-on-shell-point amplitude, are generated from a realistic one-boson-exchange (ROBE) model for pp scattering. These ROBE amplitudes are used to investigate the consequence of using different on-shell-point conditions in calculating the pp{gamma} cross sections. Purpose: We verify the validity of the ROBE pp{gamma} amplitudes. We explore similarities between the four-on-shell-point ROBE and two-u-two-t special (TuTts) soft-photon pp{gamma} amplitudes and important differences with the one-on-shell-point ROBE and Low pp{gamma} amplitudes. We demonstrate that the precision Kernfysisch Versneller Instituut (KVI) data can only be described by the four-on-shell-point (ROBE or TuTts) amplitude. We use the ROBE four-on-shell-point amplitude and one-on-shell-point amplitude to investigate systematically the effect of using different on-shell-point conditions to calculate the pp{gamma} cross section. Furthermore, we identify a general principle that governs the process. This general principle is alsomore » applicable to other bremsstrahlung processes involving the scattering of two identical nucleons. Results: (i) The four-on-shell-point ROBE (or TuTts) amplitude describes the high-precision KVI data much better than does the one-on-shell-point ROBE (or Low) amplitude. Although the contribution from the anomalous magnetic moment of the proton is very significant, it does not completely dominate the KVI pp{gamma} cross sections. (ii) The four-on-shell-point ROBE (or TuTts) amplitude describes the TRIUMF data better than does the one-on-shell-point ROBE (or Low) amplitude. (iii) The effect on the pp{gamma} cross section of using different on-shell-point conditions is significant in the hard-photon region, i.e., for small proton scattering angles {theta} (={theta}{sub 3}={theta}{sub 4}, symmetric scattering angles) far from the elastic limit ({theta}{yields}45 deg.); in contrast, the effect becomes insignificant in the vicinity of the elastic limit. Near the limit as {theta} tends to 45 deg. (or as the photon energy K approaches zero), the four-on-shell-point and one-on-shell-point amplitudes approach one another, a general principle applicable to all bremsstrahlung processes because only kinematics is involved. Conclusion: The four-on-shell-point ROBE amplitude provides a quantitative description of pp{gamma} cross sections. The anomalous magnetic moment is an important component of the photon emission mechanism. The four-on-shell-point property of the full ROBE amplitude is essential to properly describing the complete range of the precision KVI data and the TRIUMF data, although the one-on-shell-point ROBE amplitude is adequate in the region near the elastic limit.« less
28317308
Coplanar and noncoplanar nucleon-nucleon bremsstrahlung calculation: A study of pseudoscalar and pseudovector pi N couplings.
The {ital pp}{gamma} and {ital np}{gamma} processes have been used to study pseudoscalar (ps) and pseudovector (pv) {pi}{ital N} couplings. We calculate both coplanar and noncoplanar cross sections using a realistic one-boson exchange model in the energy region between 100 and 300 MeV. We find that the difference in cross sections calculated using the two couplings increases as the nucleon scattering angles decrease. Furthermore, this difference becomes greater with increasing incident energy. We show for the {ital pp}{gamma} case that this difference will be significantly increased upon the inclusion of electromagnetic form factors. For {ital pp}{gamma} with large proton scattering angles ({ge}30{degree}), cross sections (both ps and pv) calculated using an on-shell {ital p}{gamma}{ital p} vertex are in very good agreement with the data, and they are also extremely close to a recent soft-photon calculation at 157 MeV using the two-{ital u}-two-{ital t} special amplitude. The ps and pv calculations are both in good agreement with the TRIUMF data at 200 and 280 MeV. More accurate data are required to differentiate between these two couplings. Agreement with sparsely available {ital np}{gamma} data is good for most cases, but discrepancies do exist for some data points. For large nucleon scattering angles,more » noncoplanar cross sections for both {ital np}{gamma} and {ital pp}{gamma} change rapidly with the noncoplanar angle. However, the respective shapes of the noncoplanar {ital np}{gamma} and {ital pp}{gamma} curves are very different.« less
119448092
Electroweak bremsstrahlung from neutron-neutron scattering
Background: Nucleon-nucleon (NN) bremsstrahlung processes NN{gamma} (nn{gamma}, np{gamma}, and pp{gamma}) have been extensively investigated. Neutrino-pair bremsstrahlung processes from nucleon-nucleon scattering NN{nu}{nu} (nn{nu}{nu}, np{nu}{nu}, and pp{nu}{nu}) have recently attracted attention in studies of neutrino emission in neutron stars. The calculated NN{nu}{nu} cross sections (or emissivities) are found to be sensitive to the two-nucleon dynamical model used in the calculations. Purpose and Method: A realistic one-boson-exchange (ROBE) model for NN interactions is used to construct the electroweak bremsstrahlung amplitudes using the well-known nucleon electromagnetic and weak interaction vertices. The constructed nn{gamma} and nn{nu}{nu} amplitudes are investigated by applying them to calculate nn{gamma} and nn{nu}{nu} cross sections, respectively. Results: (i) The 190-MeV ROBE nn{gamma} cross sections agree well with those calculated using the TuTts amplitude, but they are in disagreement with those calculated using the Low amplitude. (ii) The calculated nn{nu}{nu} cross sections using the ROBE amplitude at the neutrino-pair energy {omega} = 1 MeV are in quantitative agreement with those calculated by Timmermans et al.[Phys. Rev. C 65, 064007 (2002)], who used the leading-order term of the soft neutrino-pair bremsstrahlung amplitude. Conclusions: The nn{gamma} amplitude in the ROBE approach, which obeys the soft-photon theorem, has a predictive power similar to that ofmore » the TuTts amplitude. The nn{nu}{nu} amplitude in the ROBE approach, which is consistent with the soft neutrino-pair bremsstrahlung theorem, has a predictive power similar to that of the soft neutrino-pair bremsstrahlung amplitude of Timmermans et al. in the low neutrino-pair energy region.« less
118708445
Jet vetoes for Higgs boson production at future hadron colliders
We study Higgs boson production in exclusive jet bins at possible future 33 and 100 TeV proton-proton colliders. We compare the cross sections obtained using fixed-order perturbation theory with those obtained by also resuming large logarithms induced by the jet-binning in the gluon-fusion and associated production channels. The central values obtained by the best-available fixed-order predictions differ by $10-20\%$ from those obtained after including resummation over the majority of phase-space regions considered. Additionally, including the resummation dramatically reduces the residual scale variation in these regions, often by a factor of two or more. We further show that in several new kinematic regimes that can be explored at these high-energy machines, the inclusion of resummation improvement is mandatory.
118435421
Improved Estimates of The $B_{(s)}\to V V$ Decays in Perturbative QCD Approach
We reexamine the branching ratios, $CP$-asymmetries, and other observables in a large number of $B_q\to VV(q=u,d,s)$ decays in the perturbative QCD (PQCD) approach, where $V$ denotes a light vector meson $(\rho, K^*, \omega, \phi)$. The essential difference between this work and the earlier similar works is of parametric origin and in the estimates of the power corrections related to the ratio $r_i^2=m_{V_i}^2/m_B^2(i=2,3)$ ($m_V$ and $m_B$ denote the masses of the vector and $B$ meson, respectively). In particular, we use up-to-date distribution amplitudes for the final state mesons and keep the terms proportional to the ratio $r_i^2$ in our calculations. Our updated calculations are in agreement with the experimental data, except for a limited number of decays which we discuss. We emphasize that the penguin annihilation and the hard-scattering emission contributions are essential to understand the polarization anomaly, such as in the $B\to \phi K^*$ and $B_s \to \phi\phi$ decay modes. We also compare our results with those obtained in the QCD factorization (QCDF) approach and comment on the similarities and differences, which can be used to discriminate between these approaches in future experiments.
37310101
DEVELOPMENT AND MEASUREMENT OF STRAIN FREE RF PHOTOINJECTOR VACUUM WINDOWS *
RF photoinjectors produce the highest brightness electron bunches only under nearly ideal illumination by a drive laser [1]. The vacuum window used to introduce the laser beam is an essential element that may potentially degrade the distribution, making it difficult or impossible to know the actual uniformity achieved at the cathode. Because of the necessity to obtain ultrahigh vacuum near the photoinjector, some restrictions are imposed on the fabrication technology available to manufacture distortion-free windows. At the UV wavelengths commonly used for photoinjectors, it is challenging to measure and eliminate degradation caused by vacuum windows. Here, we discuss the initial measurements of a strain-free, coated, UHV window manufactured by Insulator Seal in collaboration with members of Brookhaven and Argonne National Laboratories.
119294844
Matter Effects in Solar Neutrino Active-Sterile Oscillations
We study the matter effects for solar neutrino oscillations in a general scheme, without any constraint on the number of sterile neutrinos and the mixing matrix elements, only assuming a realistic hierarchy of neutrino squared-mass differences in which the smallest squared-mass difference is effective in solar neutrino oscillations. The validity of the analytic results are illustrated with a numerical solution of the evolution equation in the simplest case of four-neutrino mixing with the realistic matter density profile inside the Sun.
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.