The B-L/Electroweak Hierarchy in Smooth Heterotic Compactifications

E8 X E8 heterotic string and M-theory, when appropriately compactified, can give rise to realistic, N=1 supersymmetric particle physics. In particular, the exact matter spectrum of the MSSM, including three right-handed neutrino supermultiplets, one per family, and one pair of Higgs-Higgs conjugate superfields is obtained by compactifying on Calabi-Yau manifolds admitting specific SU(4) vector bundles. These "heterotic standard models" have the SU(3)_{C} X SU(2)_{L} X U(1)_{Y} gauge group of the standard model augmented by an additional gauged U(1)_{B-L}. Their minimal content requires that the B-L gauge symmetry be spontaneously broken by a vacuum expectation value of at least one right-handed sneutrino. In a previous paper, we presented the results of a renormalization group analysis showing that B-L gauge symmetry is indeed radiatively broken with a B-L/electroweak hierarchy of O(10) to O(10^{2}). In this paper, we present the details of that analysis, extending the results to include higher order terms in tan[beta]^{-1} and the explicit spectrum of all squarks and sleptons.Comment: 60 pages, 6 figure

Rescattering and finite formation time effects in electro-disintegration of the deuteron in the cumulative region

The role of rescattering due to the final state interaction (FSI) and the influence of the finite formation time (FFT) on the inclusive $D(e,e')X$ and exclusive $D(e,e'p)n$ electro-disintegration of the deuteron are studied in the cumulative kinematical region $x>1$ and moderate values of the 4-momentum transfer $Q^2=2\div 10$ (GeV/c)$^2$. The spins are averaged out. It is found that in the inclusive process the relative magnitude of rescattering steadily grows with $x$ and that at $x=1.7$ it has the same order as the plane wave impulse approximation (PWIA) contribution, with the finite formation time effects decreasing the rescattering contribution by $\sim 30$%. In the exclusive process, with increasing momentum transfer, FFT substantially reduces the effects from FSI, although the latter are still appreciable in the region of momentum transfer investigated.Comment: 5 pages, 5 EPS figures. Presented by M. A. Braun at the Fourth International Conference on Hadronic Physics, Trieste (Italy), ICTP May 12-16, 2003. To appear in EPJ

The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum

We investigate the leading-twist light-cone distribution amplitudes for the pion and kaon, based on the nonlocal chiral quark model from the instanton vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into account. The Gegenbauer moments are computed, analyzed and compared with those of other models. The one-loop QCD evolution of the moments is briefly discussed. The transverse momentum distributions are also discussed for the pion and kaon light-cone wave functions.Comment: 17 pages, 12 figures. Accepted for publication in Physical Review

Towards the theory of coherent hard dijet production on hadrons and nuclei

We carry out a detailed calculation of the cross section of pion diffraction dissociation into two jets with large transverse momenta, originating from a hard gluon exchange between the pion constituents. Both the quark and the gluon contribution are considered and in the latter case we present calculations both in covariant and in axial gauges. We find that the standard collinear factorization does not hold in this reaction. The structure of non-factorizable contributions is discussed and the results are compared with the experimental data. Our conclusion is that the existing theoretical uncertainties do not allow, for the time being, for a quantitative extraction of the pion distribution amplitude.Comment: 45 pages, latex, 17 figures, final version to appear in Nuclear Physics

Elliptic flow from color strings

It is shown that the elliptic flow can be successfully described in the color string picture with fusion and percolation provided anisotropy of particle emission from the fused string is taken into account. Two possible sources of this anisotropy are considered, propagation of the string in the transverse plane and quenching of produced particles in the strong color field of the string. Calculations show that the second source gives an overwhelming contribution to the flow at accessible energies.Comment: 23 pages, 11 figure

The Exact MSSM Spectrum from String Theory

We show the existence of realistic vacua in string theory whose observable sector has exactly the matter content of the MSSM. This is achieved by compactifying the E_8 x E_8 heterotic superstring on a smooth Calabi-Yau threefold with an SU(4) gauge instanton and a Z_3 x Z_3 Wilson line. Specifically, the observable sector is N=1 supersymmetric with gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}, three families of quarks and leptons, each family with a right-handed neutrino, and one Higgs-Higgs conjugate pair. Importantly, there are no extra vector-like pairs and no exotic matter in the zero mode spectrum. There are, in addition, 6 geometric moduli and 13 gauge instanton moduli in the observable sector. The holomorphic SU(4) vector bundle of the observable sector is slope-stable.Comment: 15 pages, LaTeX; v2: Hidden sector is unstable, symbol typesetting error corrected, clarifications and references added; v3: New discussion of hidden secto

Cumulative structure function in terms of nucleonic wave function of the nucleus

The structure function of the nucleus in the cumulative region $x>1$ is studied in terms of nucleon degrees of freedom. At high $Q^2$ the resulting expressions are presented as a sum of contributions from few-nucleon correlations. Two-nucleon correlations are studied in some detail. Spin variables are averaged out. In the region $1<x<2$ the structure functions are calculated for the relativistic interaction proposed by F.Gross {\it et al}. They are found to fall with $x$ faster than the exponential. For Carbon at $x=1.05$, where the method is not rigorously applicable, they turn out to be rougly twice larger than the experimental data.Comment: text and 2 figures in LaTex, 7 figures in P

Exploring Time-Sensitive Variational Bayesian Inference LDA for Social Media Data

There is considerable interest among both researchers and the mass public in understanding the topics of discussion on social media as they occur over time. Scholars have thoroughly analysed sampling-based topic modelling approaches for various text corpora including social media; however, another LDA topic modelling implementation—Variational Bayesian (VB)—has not been well studied, despite its known efficiency and its adaptability to the volume and dynamics of social media data. In this paper, we examine the performance of the VB-based topic modelling approach for producing coherent topics, and further, we extend the VB approach by proposing a novel time-sensitive Variational Bayesian implementation, denoted as TVB. Our newly proposed TVB approach incorporates time so as to increase the quality of the generated topics. Using a Twitter dataset covering 8 events, our empirical results show that the coherence of the topics in our TVB model is improved by the integration of time. In particular, through a user study, we find that our TVB approach generates less mixed topics than state-of-the-art topic modelling approaches. Moreover, our proposed TVB approach can more accurately estimate topical trends, making it particularly suitable to assist end-users in tracking emerging topics on social media