Cabibbo suppressed decays and the Ξc+\Xi_{c}^{+} lifetime

The problem of the $\Xi_{c}^{+}$ lifetime is considered in the framework of {\em Heavy-Quark Expansion} and $SU(3)_{flavor}$ symmetry. The lifetime of $\Xi_{c}^{+}$ is expressed in terms of measurable inclusive quantities of the other two charmed baryons belonging to the same $SU(3)_{flavor}$ multiplet in a model-independent way. In such a treatment, inclusive decay rates of singly Cabibbo suppressed decay modes have a prominent role. An analogous approach is applied to the multiplet of charmed mesons yielding interesting predictions on $D_{s}^{+}$ properties. The results obtained indicate that a more precise measurement of inclusive decay quantities of some charmed hadrons (such as $\Lambda_{c}^{+}$) that are more amenable to experiment can contribute significantly to our understanding of decay properties of other charmed hadrons (such as $\Xi_{c}^{+}$) where discrepancies or ambiguities exist.Comment: 9 pages, revtex4; certain improvements in text as suggested by the referee, acknowledgement changed; version to appear in Phys. Rev.

Holography and Variable Cosmological Constant

An effective local quantum field theory with UV and IR cutoffs correlated in accordance with holographic entropy bounds is capable of rendering the cosmological constant (CC) stable against quantum corrections. By setting an IR cutoff to length scales relevant to cosmology, one easily obtains the currently observed rho_Lambda ~ 10^{-47} GeV^4, thus alleviating the CC problem. It is argued that scaling behavior of the CC in these scenarios implies an interaction of the CC with matter sector or a time-dependent gravitational constant, to accommodate the observational data.Comment: 7 pages, final version accepted by PR

Exclusive Double Charmonium Production from Υ\Upsilon Decay

The exclusive decay of $\Upsilon$ to a vector plus pseudoscalar charmonium is studied in perturbative QCD. The corresponding branching ratios are predicted to be of order $10^{-6}$ for first three $\Upsilon$ resonances, and we expect these decay modes should be discovered in the prospective high-luminosity $e^+e^-$ facilities such as super $B$ experiment. As a manifestation of the short-distance loop contribution, the relative phases among strong, electromagnetic and radiative decay amplitudes can be deduced. It is particularly interesting to find that the relative phase between strong and electromagnetic amplitudes is nearly orthogonal. The resonance-continuum interference effect for double charmonium production near various $\Upsilon$ resonances in $e^+e^-$ annihilation is addressed

Agegraphic Chaplygin gas model of dark energy

We establish a connection between the agegraphic models of dark energy and Chaplygin gas energy density in non-flat universe. We reconstruct the potential of the agegraphic scalar field as well as the dynamics of the scalar field according to the evolution of the agegraphic dark energy. We also extend our study to the interacting agegraphic generalized Chaplygin gas dark energy model.Comment: 8 page

Gluon Fragmentation into Heavy Quarkonium

The dominant production mechanism for heavy quark-antiquark bound states in very high energy processes is fragmentation, the splitting of a high energy parton into a quarkonium state and other partons. We show that the fragmentation functions $D(z,\mu)$ describing these processes can be calculated using perturbative QCD. We calculate the fragmentation functions for a gluon to split into S-wave quarkonium states to leading order in the QCD coupling constant. The leading logarithms of $\mu/m_Q$, where $\mu$ is the factorization scale and $m_Q$ is the heavy quark mass, are summed up using Altarelli-Parisi evolution equations.Comment: LateX 11 pages (3 figures available upon request). NUHEP-TH-92-2

Nonsaturated Holographic Dark Energy

It has been well established by today that the concept of holographic dark energy (HDE) does entail a serious candidate for the dark energy of the universe. Here we deal with models where the holographic bound for dark energy is not saturated for a large portion of the history of the universe. This is particularly compelling when the IR cutoff is set by the Hubble scale, since otherwise a transition from a decelerated to an accelerated era cannot be obtained for a spatially flat universe. We demonstrate by three generic but disparate dynamical models, two of them containing a variable Newton constant, that transition between the two eras is always obtained for the IR cutoff in the form of the Hubble scale and the nonsaturated HDE. We also give arguments of why such a choice for the dark energy is more consistent and favored over the widely accepted saturated form.Comment: 9 pages, minor revision, to appear in JCA

Thermodynamics of interacting entropy-corrected holographic dark energy in a non-flat FRW universe

A so-called "entropy-corrected holographic dark energy" (ECHDE), was recently proposed to explain the dark energy-dominated universe with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate its thermodynamical features including entropy and energy conservation. We describe the thermodynamical interpretation of the interaction between ECHDE and dark matter in a non-flat universe. We obtain a relation between the interaction term of the dark components and thermal fluctuation. Our study further generalizes the earlier works [M.R. Setare and E.C. Vagenas, Phys. Lett. B 666 (2008) 111; B. Wang et al., Phys. Lett. B 662 (2008) 1] in this direction.Comment: 14 pages, no figure, accepted by Int. J. Mod. Phys.

A Tracker Solution for a Holographic Dark Energy Model

We investigate a kind of holographic dark energy model with the future event horizon the IR cutoff and the equation of state -1. In this model, the constraint on the equation of state automatically specifies an interaction between matter and dark energy. With this interaction included, an accelerating expansion is obtained as well as the transition from deceleration to acceleration. It is found that there exists a stable tracker solution for the numerical parameter $d>1$, and $d$ smaller than one will not lead to a physical solution. This model provides another possible phenomenological framework to alleviate the cosmological coincidence problem in the context of holographic dark energy. Some properties of the evolution which are relevant to cosmological parameters are also discussed.Comment: 10 pages, 3 figures; accepted for publication in Int.J.Mod.Phys.

Radiative Decay of Vector Quarkonium: Constraints on Glueballs and Light Gluinos

Given a resonance of known mass, width, and J^{PC}, we can determine its gluonic branching fraction, b(R->gg), from data on its production in radiative vector quarkonium decay, V -> gamma+R. For most resonances b(R->gg) is found to be O(10%), consistent with being q-qbar states, but we find that both pseudoscalars observed in the 1440 MeV region have b(R->gg) ~ 1/2 - 1, and b(f_0^{++}->gg) ~ 1/2. As data improves, b(R->gg) should be a useful discriminator between q-qbar and gluonic states and may permit quantitative determination of the extent to which a particular resonance is a mixture of glueball and q-qbar. We also examine the regime of validity of pQCD for predicting the rate of V -> gamma+eta_gluino, the ``extra'' pseudoscalar bound state which would exist if there were light gluinos. From the CUSB limit on peaks in Upsilon -> gamma X, the mass range 3 GeV < m(eta_gluino) < 7 GeV can be excluded. An experiment must be significantly more sensitive to exclude an eta_gluino lighter than this.Comment: 36pp (inc figs),RU-94-04. (Replaces original which didn't latex correctly and didn't have figures.

Cabibbo-suppressed decays of the Omega_c^0 - feedback to the Xi_c^+ lifetime

We investigate a possible background of the type Omega_c^0 --> Xi_c^+ pi^- to the CLEO Xi_c^+ lifetime measurement. This decay mode may lead to an overestimate of the Xi_c^+ decay length and, therefore, increase the measured Xi_c^+ lifetime. The branching ratio Gamma(Omega_c^0 --> Xi_c^+ pi^-)/Gamma(Omega_c^0 --> Omega^- pi^+) is analyzed in the framework of the pole model and the modified current algebra. We find that the Omega_c^0 --> Xi_c^+ pi^- decay mode could not generate a substantial systematic error in the Xi_c^+ lifetime measurement. Also, it cannot significantly reduce the disagreement between theoretical and experimental values of the Xi_c^+ lifetime.Comment: 9 pages, 3 figure