The PAMELA excess from neutralino annihilation in the NMSSM

We examine whether the cosmic ray positron excess observed by PAMELA can be explained by neutralino annihilation in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). The main dark matter annihilation products are the lightest CP-even scalar h1 plus the lightest CP-odd scalar a1, with the a1 decaying into two muons. The energetic positrons needed to explain PAMELA are thus obtained in the NMSSM simply from kinematics. The required large annihilation cross section is obtained from an s-channel resonance with the heavier CP-odd scalar a2. Various experiments constrain the PAMELA-favored NMSSM parameter space, including collider searches for a light a1. These constraints point to a unique corner of the NMSSM parameter space, having a lightest neutralino mass around 160 GeV and a very light pseudoscalar mass less than a GeV. A simple parameterized formula for the charge-dependent solar modulation effects reconciles the discrepancy between the PAMELA data and the estimated background at lower energies. We also discuss the electron and gamma ray spectra from the Fermi LAT observations, and point out the discrepancy between the NMSSM predictions and Fermi LAT preliminary results and possible resolution. An NMSSM explanation of PAMELA makes three striking and uniquely correlated predictions: the rise in the PAMELA positron spectrum will turn over at around 70 GeV, the dark matter particle mass is less than the top quark mass, and a light sub-GeV pseudoscalar will be discovered at colliders.Comment: 25 pages, 9 figures; final version for PR

Perturbative QCD Analysis of the Nucleon's Pauli Form Factor F_2(Q^2)

We perform a perturbative QCD analysis of the nucleon's Pauli form factor $F_2(Q^2)$ in the asymptotically large $Q^2$ limit. We find that the leading contribution to $F_2(Q^2)$ has a $1/Q^6$ power behavior, consistent with the well-known result in the literature. Its coefficient depends on the leading- and subleading-twist light-cone wave functions of the nucleon, the latter describing the quarks with one unit of orbital angular momentum. We also derive at the logarithmic accurary the asymptotic scaling $F_2(Q^2)/F_1(Q^2) \sim (\log^2 Q^2/\Lambda^2)/Q^2$ which describes recent Jefferson Lab data well.Comment: 4 papes, 3 figures include

Light Cone Sum Rules for gamma* N -> Delta Transition Form Factors

A theoretical framework is suggested for the calculation of gamma* N -> Delta transition form factors using the light-cone sum rule approach. Leading-order sum rules are derived and compared with the existing experimental data. We find that the transition form factors in a several GeV region are dominated by the ``soft'' contributions that can be thought of as overlap integrals of the valence components of the hadron wave functions. The ``minus'' components of the quark fields contribute significantly to the result, which can be reinterpreted as large contributions of the quark orbital angular momentumComment: 38 pages, 10 figures; some typos fixed and references added, to appear in Phys. Rev.

Charm and Bottom Semileptonic Decays

We review the present status of theoretical attempts to calculate the semileptonic charm and bottom decays and then present a calculation of these decays in the light--front frame at the kinematic point $q^2=0$. This allows us to evaluate the form factors at the same value of $q^2$, even though the allowed kinematic ranges for charm and bottom decays are very different. Also, at this kinematic point the decay is given in terms of only one form factor $A_{0}(0)$. For the ratio of the decay rates given by the E653 collaboration we show that the determination of the ratio of the Cabibbo--Kobayashi--Maskawa (CKM) matrix elements is consistent with that obtained from the unitarity constraint. At present, though, the unitarity method still has greater accuracy. Since comparisons of the semileptonic decays into $\rho$ and either electrons or muons will be available soon from the E791 Fermilab experiment, we also look at the massive muon case. We show that for a range of $q^2$ the $SU(3)_F$ symmetry breaking is small even though the contributions of the various helicity amplitudes becomes more complicated. For $B$ decays, the decay $B \rightarrow K^{*} \ell \bar{\ell}$ at $q^2=0$ involves an extra form factor coming from the photon contribution and so is not amenable to the same kind of analysis, leaving only the decay $B \rightarrow K^{*}\nu \bar{\nu}$ as a possibility. As the mass of the decaying particle increases we note that the $SU(3)$ symmetry becomes badly broken at $q^2=0$.Comment: Latex, 19 pages, two figures are attached, a minor change in the manuscript related to thi

Weak Decays in the light--front Quark Model

We study the form factors of heavy--to--heavy and heavy--to--light weak decays using the light--front relativistic quark model. For the heavy--to--heavy B \ra D^{(\ast)} semileptonic decays we calculate the corresponding Isgur--Wise function for the whole kinematic region. For the heavy--to--light B\ra P and B\ra V semileptonic decays we calculate the form factors at $q^2 = 0$; in particular, we have derived the dependence of the form factors on the $b$--quark mass in the m_b \ra \infty limit. This dependence can not be produced by extrapolating the scaling behavior of the form factors at $q^2_{max}$ using the single--pole assumption. This shows that the $q^2$ dependence of the form factors in regions far away from the zero--recoil could be much more complicated than that predicted by the single--pole assumption.Comment: 24 pages, Latex, Postscript figure included at the en

Soft Contribution to Form Factors of γ∗p→Δ+\gamma^* p \to \Delta^+ Transition

The purely nonperturbative soft contribution to the $\gamma^* p \to \Delta^+$ transition form factors is estimated using the local quark-hadron duality approach. Our results show that the soft contribution is dominated by the magnetic transition: the ratio $G_E^*(Q^2)/G_M^*(Q^2)$ is small for all accessible $Q^2$, in contrast to pQCD expectations that $G_E^*(Q^2) \to -G_M^*(Q^2)$. We also found that the soft contribution to the magnetic form factor is large enough to explain the magnitude of existing experimental data.Comment: 29 pages, REVTeX, 5 eps-figures in uuencoded gz-compressed .tar fil