465 research outputs found
Hadron Structure on the Lattice
A few chosen nucleon properties are described from a lattice QCD perspective:
the nucleon sigma term and the scalar strangeness in the nucleon; the vector
form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the
Collaborative Research Center 443 "Many-body structure of strongly
interacting systems", Mainz, February 23-25, 201
Phase diagram and optical conductivity of the one-dimensional spinless Holstein model
The effects of quantum lattice fluctuations on the Peierls transition and the
optical conductivity in the one-dimensional Holstein model of spinless fermions
have been studied by developing an analytical approach, based on the unitary
transformation method. We show that when the electron-phonon coupling constant
decreases to a finite critical value the Peierls dimerization is destroyed by
the quantum lattice fluctuations. The dimerization gap is much more reduced by
the quantum lattice fluctuations than the phonon order parameter. The
calculated optical conductivity does not have the inverse-square-root
singularity but have a peak above the gap edge and there exists a significant
tail below the peak. The peak of optical-conductivity spectrum is not directly
corresponding to the dimerized gap. Our results of the phase diagram and the
spectral-weight function agree with those of the density matrix renormalization
group and the exact diagonalization methods.Comment: 9 pages, 4 figures include
Heavy Quark production at the TEVATRON and HERA using k_t-factorization with CCFM evolution
The application of k_t-factorization supplemented with the CCFM small-x
evolution equation to heavy quark production at the TEVATRON and at HERA is
discussed. The bb_bar production cross sections at the TEVATRON can be
consistently described using the k_t-factorization formalism together with the
unintegrated gluon density obtained within the CCFM evolution approach from a
fit to HERA F_2 data. Special attention is drawn to the comparison with
measured visible cross sections, which are compared to the hadron level Monte
Carlo generator CASCADEComment: 13 pages, updated references and updated Fig. 9, Fig. 2 replace
The size of electron-hole pairs in pi conjugated systems
We have performed momentum dependent electron energy-loss studies of the
electronic excitations in sexithiophene and compared the results to those from
parent oligomers. Our experiment probes the dynamic structure factor
S(q,omega)and we show that the momentum dependent intensity variation of the
excitations observed can be used to extract the size of the electron-hole pair
created in the excitation process. The extension of the electron-hole pairs
along the molecules is comparable to the length of the molecules and thus maybe
only limited by structural constraints. Consequently, the primary
intramolecular electron-hole pairs are relatively weakly bound. We find no
evidence for the formation of excitations localized on single thiophene units.Comment: RevTex, 3 figures, to appear in Physical Review Letter
On the mechanisms of heavy-quarkonium hadroproduction
We discuss the various mechanisms potentially at work in hadroproduction of
heavy quarkonia in the light of computations of higher-order QCD corrections
both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the
inclusion of the contribution arising from the s-channel cut in the CS channel.
We also discuss new observables meant to better discriminate between these
different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And
Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June
2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses
svjour.cls and svepj.clo (included
Quark Soup al dente: Applied Superstring Theory
We discuss the application of the AdS/CFT correspondence to possibly gain new
physical insights for the strongly coupled quark-gluon plasma. This article
provides an informal summary of a talk given by RCM at the 18th International
Conference on General Relativity and Gravitation in July 2007.Comment: This article provides an informal summary of a talk given by RCM at
the 18th International Conference on General Relativity and Gravitation in
July 200
Ab-initio calculation of the electronic and optical excitations in polythiophene: effects of intra- and interchain screening
We present an calculation of the electronic and optical excitations of an
isolated polythiophene chain as well as of bulk polythiophene. We use the GW
approximation for the electronic self-energy and include excitonic effects by
solving the electron-hole Bethe-Salpeter equation. The inclusion of interchain
screening in the case of bulk polythiophene drastically reduces both the
quasi-particle band gap and the exciton binding energies, but the optical gap
is hardly affected. This finding is relevant for conjugated polymers in
general.Comment: 4 pages, 1 figur
Long-lived photoexcited states in polydiacetylenes with different molecular and supramolecular organization
With the aim of determining the importance of the molecular and supramolecular organization on the excited states of polydiacetylenes, we have studied the photoinduced absorption spectra of the red form of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) and the results compared with those of the blue form of the same polymer. An interpretation of the data is given in terms of both the conjugation length and the interbackbone separation also in relation to the photoinduced absorption spectra of both blue and red forms of poly[1,6-bis(N-carbazolyl)-2,4-hexadiyne] (polyDCHD), which does not carry the alkyl substituents on the carbazolyl side groups. Information on the above properties is derived from the analysis of the absorption and Raman spectra of this class of polydiacetylenes
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