781 research outputs found
A new chiral ligand: 2,6-bis 4(S)-isopropyl-1-phenyl-4,5-dihydro-1H-imidazol-2-yl pyridine
The title compound, C29H33N5, is a new chiral bis(imidazolyl) pyridine derivative with a skeleton similar to the bis(oxazolyl) pyridine derivatives, which have been extensively used as ligands in various asymmetric catalytic reactions. The most prominent feature of the present compound is the considerable sp(2) character of N atoms of the imidazoline rings. The substituents at the Nsp(2) atoms can provide a means for tuning the electronic and conformational properties of the compound
Kaluza-Klein gravitino production with a single photon at e^+ e^- colliders
In a supersymmetric large extra dimension scenario, the production of
Kaluza-Klein gravitinos accompanied by a photino at e^+ e^- colliders is
studied. We assume that a bulk supersymmetry is softly broken on our brane such
that the low-energy theory resembles the MSSM. Low energy supersymmetry
breaking is further assumed as in GMSB, leading to sub-eV mass shift in each KK
mode of the gravitino from the corresponding graviton KK mode. Since the
photino decays within a detector due to its sufficiently large inclusive decay
rate into a photon and a gravitino, the process e^+ e^- -> photino + gravitino
yields single photon events with missing energy. Even if the total cross
section can be substantial at sqrt(s)=500 GeV, the KK graviton background of
e^+ e^- -> photon + graviton is kinematically advantageous and thus much
larger. It is shown that the observable, sigma(e^-_L)-sigma(e^-_R), can
completely eliminate the KK graviton background but retain most of the KK
gravitino signal, which provides a unique and robust method to probe the
supersymmetric bulk.Comment: Reference added and typos correcte
A New Type of Dark Energy Model
In this paper, we propose a general form of the equation of state (EoS) which
is the function of the fractional dark energy density . At least,
five related models, the cosmological constant model, the holographic dark
energy model, the agegraphic dark energy model, the modified holographic dark
energy model and the Ricci scalar holographic dark energy model are included in
this form. Furthermore, if we consider proper interactions, the interactive
variants of those models can be included as well. The phase-space analysis
shows that the scaling solutions may exist both in the non-interacting and
interacting cases. And the stability analysis of the system could give out the
attractor solution which could alleviate the coincidence problem.Comment: Minor modifications, references adde
Photoproduction in Scattering
We investigate the + c + photoproduction in
collision at the LEP II energy. The physical motivations for this study are: 1)
such next-to-leading order(NLO) process was not considered in previous
investigations of photoproduction in interaction, and it is
worthwhile to do so in order to make sound predictions for experimental
comparison; 2) from recent Belle experiment results, the process with same
final states at the factory has a theoretically yet unexplainable large
fraction; hence it is interesting to see what may happen at other colliders; 3)
the existing LEP data are marginal in observing such process, and at the planed
Linear Colliders(LCs) this process can be measured with high accuracy; 4) it is
necessary to take this process into consideration in the aim of elucidating the
quarkonium production mechanism, especially in testing the universality of
NRQCD nonperturbative matrix elements via photoproduction in
electron-position collisions.Comment: 15 pages, 3 figure
Inclusive Charmonium Production via Double in Annihilation
Motivated by the recent observation of double charm quark pair production by
the Belle Collaboration, we calculate the complete
inclusive production cross sections for , , and
(J=0, 1, 2) plus in annihilation through a
virtual photon. We consider both color-singlet and color-octet contributions,
and give the analytical expressions for these cross sections. The complete
color-singlet calculations are compared with the approximate fragmentation
calculations as functions of the center-of-mass energy . We find that
most of the fragmentation results substantially overestimate the cross sections
(e.g. by a factor of 4 for and ) at the Belle and
BaBar energy GeV. The fragmentation results become a good
approximation only when is higher than about 100GeV. We further
calculate the color-octet contributions to these cross sections with analytical
expressions. We find that while the color-octet contribution to
inclusive production via double charm is negligible (only about 3%), the
color-octet contributions to and can be significant.Comment: 23 pages, 9 figures; color-octet contributions to the double charm
inclusive production of J/psi and chi_{cJ} (J=0,1,2) are added; references
are added; No change for the color-singlet par
Statefinder diagnostic and stability of modified gravity consistent with holographic and new agegraphic dark energy
Recently one of us derived the action of modified gravity consistent with the
holographic and new-agegraphic dark energy. In this paper, we investigate the
stability of the Lagrangians of the modified gravity as discussed in [M. R.
Setare, Int. J. Mod. Phys. D 17 (2008) 2219; M. R. Setare, Astrophys. Space
Sci. 326 (2010) 27]. We also calculate the statefinder parameters which
classify our dark energy model.Comment: 12 pages, 2 figures, accepted by Gen. Relativ. Gravi
Novel venom-derived inhibitors of the human EAG channel, a putative antiepileptic drug target
Recently, we and other groups revealed that gain-of-function mutations in the human ether à go-go voltage-gated potassium channel hEAG1 (K10.1) lead to developmental disorders with associated infantile-onset epilepsy. However, the physiological role of hEAG1 in the central nervous system remains elusive. Potent and selective antagonists of hEAG1 are therefore much sought after, both as pharmacological tools for studying the (patho)physiological functions of this enigmatic channel and as potential leads for development of anti-epileptic drugs. Since animal venoms are a rich source of potent ion channel modifiers that have been finely tuned by millions of year of evolution, we screened 108 arachnid venoms for hEAG1 inhibitors using electrophysiology. Two hit peptides (Aa1a and Ap1a) were isolated, sequenced, and chemically synthesised for structure-function studies. Both of these hEAG1 inhibitors are C-terminally amidated peptides containing an inhibitor cystine knot motif, which provides them with exceptional stability in both plasma and cerebrospinal fluid. Aa1a and Ap1a are the most potent peptidic inhibitors of hEAG1 reported to date, and they present a novel mode of action by targeting both the activation and inactivation gating of the channel. These peptides should be useful pharmacological tools for probing hEAG1 function as well as informative leads for the development of novel anti-epileptic drugs
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment
This paper describes an analysis of the angular distribution of W->enu and
W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with
the ATLAS detector at the LHC in 2010, corresponding to an integrated
luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and
the missing transverse energy, the W decay angular distribution projected onto
the transverse plane is obtained and analysed in terms of helicity fractions
f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV
and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw
> 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour,
are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017
+/- 0.030, where the first uncertainties are statistical, and the second
include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables,
revised author list, matches European Journal of Physics C versio
Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS
The chi_b(nP) quarkonium states are produced in proton-proton collisions at
the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS
detector. Using a data sample corresponding to an integrated luminosity of 4.4
fb^-1, these states are reconstructed through their radiative decays to
Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks
corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new
structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is
also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes.
This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table,
corrected author list, matches final version in Physical Review Letter
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