85 research outputs found
Electric communication during courtship and spawning in two sibling species of dwarf stonebasher from southern Africa, Pollimyrus castelnaui and P. marianne (Mormyridae, Teleostei): evidence for a non species-specific communication code?
The fixed part of the electrocommunication signal, the electric organ discharge (EOD) waveform, is well differentiated in the two vicariant dwarf stonebasher species, Pollimyrus castelnaui and P. marianne. However, differentiation regarding the variable, situation-dependent part, i.e., inter-discharge interval (IDI) patterns, has never been studied in a pair of sibling species of mormyrid fish. We here compare the electrical signalling that accompanies different motor behaviours (such as resting and swimming, territorial agonistic interactions, courtship and spawning) in the two species. Double pulse patterns of regularly alternating short IDIs of 8-11 ms and long ones of 16-100 ms accompanied threat displays in both species. In three pairs of P. marianne and five pairs of P. castelnaui, courtship was characterised by nest building, territory patrolling and acoustic displays (advertisment calls) that were accompanied by long discharge breaks in the male and highly regular IDIs around 50 ms in the female of both species. Nest-tending males showed IDI sequences consisting of regularly alternating double pulse patterns, similar to threat displays. During spawning both sexes generated stereotyped IDI sequences of a low discharge rate. All IDI patterns occurring in one species were also found in the other, and no species-specifity was identified at that level. Playback experiments contrasting conspecific and heterospecific IDI sequences (that had been recorded from nocturnally swimming fish) revealed preferences in none of the six experimental subjects. Double pulse patterns, high discharge rate displays (HD) and regularisations of the IDI sequence accompanying specific behaviours occurred in similar form in both dwarf stonebasher species of the present study. Therefore, we conclude that in the speciation of P. castelnaui and P. marianne the fixed part of the EOD, its waveform, was under more differential selection pressure than its variable part, the patterns of IDI
J/psi Inclusive Production in nu N Neutral-Current Deep-Inelastic Scattering
We calculate the cross section of J/psi inclusive production in
neutrino-nucleon deep-inelastic scattering via the weak neutral current within
the factorization formalism of nonrelativistic quantum chromodynamics. Besides
J/psi single production via the Z-gluon fusion mechanism, we also consider
J/psi plus hadron-jet associated production. We take into account both direct
production and feed-down from directly-produced heavier charmonia. We present
theoretical predictions for the J/psi transverse-momentum and rapidity
distributions, which can be measured in the CHORUS and NOMAD experiments at
CERN, including conservative error estimates. In order to interpret a recent
CHORUS measurement of the total cross section, we also estimate the
contribution due to J/psi prompt production via diffractive processes using the
vector-meson dominance model.Comment: 34 pages (Latex), 5 figures (Postscript); significantly extended to
include feed-down and diffractive contributions and nuclear corrections;
accepted for publication in Nucl. Phys.
Color-Octet Contributions to J/psi Photoproduction via Fragmentation at HERA
We study J/psi photoproduction via fragmentation at next-to-leading order in
the QCD-improved parton model, using the nonrelativistic factorization
formalism proposed by Bodwin, Braaten, and Lepage. We consider direct and
resolved photoproduction of prompt J/psi mesons and chi_{cJ} mesons radiatively
decaying to J/psi+gamma, taking into account the formation of both
color-singlet and color-octet c anti-c states. Adopting the values of the
long-distance color-octet matrix elements extracted from fits to prompt-J/psi
data recently taken at the Fermilab Tevatron, we predict that measurements of
J/psi photoproduction at DESY HERA should show a distinctive excess over the
expectation based on the color-singlet model at small values of the
inelasticity variable z. This is complementary to the expected enhancement at z
close to 1 due to the color-octet contribution to photon-gluon fusion.Comment: 10 pages (Latex), 3 figures (Postscript
J/psi Inclusive Production in ep Deep-Inelastic Scattering at DESY HERA
We calculate the cross section of J/psi plus jet associated production in ep
deep-inelastic scattering within the factorization formalism of nonrelativistic
quantum chromodynamics. Our analytic results disagree with previous analyses,
both for the colour-singlet and colour-octet channels. Our theoretical
predictions agree reasonably well with recent data taken by the H1
Collaboration at DESY HERA, significantly better than those obtained within the
colour-singlet model.Comment: 27 pages (Latex), 9 figures (Postscript), to appear in Nucl. Phys.
Charmonium Production via Fragmentation at DESY HERA
The cross section for the photoproduction of large-p_T J/psi mesons at HERA
is calculated at next-to-leading order, adopting a perturbative approach to
describe the fragmentation of charm quarks and gluons into J/psi mesons. We
treat the charm quark according to the massless factorization scheme, where it
is assumed to be one of the active flavours inside the proton and the resolved
photon. We present inclusive distributions in transverse momentum and rapidity,
including the contributions due to direct and resolved photons. The importance
of the colour-octet components of the J/psi wave function, which contribute to
the fragmentation process, is emphasized. In addition to prompt J/psi
production, we consider also the production of chi_{cJ} states followed by
radiative decays to J/psi mesons, both in the colour-singlet and colour-octet
channels.Comment: 32 pages (Latex), 12 figures (Postscript
Strong Coupling Constant from Scaling Violations in Fragmentation Functions
We present a new determination of the strong coupling constant alpha_s
through the scaling violations in the fragmentation functions for charged
pions, charged kaons, and protons. In our fit we include the latest e+e-
annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and
older, yet very precise data from SLAC PEP at center-of-mass energy sqrt(s)=29
GeV. A new world average of alpha_s is given.Comment: 10 pages, 3 eps figue
Heavy-quark contributions to the ratio F_L/F_2 at low x
We study the heavy-quark contribution to the proton structure functions
F_2^i(x,Q^2) and F_L^i(x,Q^2), with i=c,b, for small values of Bjorken's x
variable at next-to-lading order and provide compact formulas for their ratios
R_i=F_L^i/F_2^i that are useful to extract F_2^i(x,Q^2) from measurements of
the doubly differential cross section of inclusive deep-inelastic scattering at
DESY HERA. Our approach naturally explains why R_i is approximately independent
of x and the details of the parton distributions in the small-x regime.Comment: 11 pages, 1 figur
Associated Production of Heavy Quarkonia and Electroweak Bosons at Present and Future Colliders
We investigate the associated production of heavy quarkonia, with
angular-momentum quantum numbers ^{2S+1}L_J = ^1S_0, ^3S_1, ^1P_1, ^3P_J (J =
0, 1, 2), and photons, Z bosons, and W bosons in photon-photon, photon-hadron,
and hadron-hadron collisions within the factorization formalism of
nonrelativistic quantum chromodynamics providing all contributing partonic
cross sections in analytic form. In the case of photoproduction, we also
include the resolved-photon contributions. We present numerical results for the
processes involving J/psi and chi_{cJ} mesons appropriate for the Fermilab
Tevatron, CERN LHC, DESY TESLA, operated in the e^+ e^- and gamma gamma modes,
and DESY THERA.Comment: 41 pages (Latex), 10 figures (Postscript
J/psi plus prompt-photon associated production in two-photon collisions at next-to-leading order
We calculate the cross section of J/psi plus prompt-photon inclusive
production in gamma gamma collisions at next-to-leading order within the
factorization formalism of nonrelativistic quantum chromodynamics (NRQCD)
focusing on direct photoproduction. Apart from direct J/psi production, we also
include the feed-down from directly-produced chi_{cJ} and psi' mesons. We
discuss the analytical calculation, in particular the treatment of the various
types of singularities and the NRQCD operator renormalization, in some detail.
We present theoretical predictions for the future e^+e^- linear collider TESLA,
taking into account both brems- and beamstrahlung.Comment: 31 pages, 9 figure
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