8,143 research outputs found
A diquark model for baryons containing one heavy quark
We present a phenomenological ansatz for coupling a heavy quark with two
light quarks to form a heavy baryon. The heavy quark is treated in the heavy
mass limit, and the light quark dynamics is approximated by propagating scalar
and axial vector 'diquarks'. The resulting effective lagrangian, which
incorporates heavy quark and chiral symmetry, describes interactions of heavy
baryons with Goldstone bosons in the low energy region. As an application, the
Isgur--Wise form factors are estimated.Comment: 9 pages + 8 figures, both as uuencoded PS, discussion of Bjorken
limit (1 par + 1 fig) added, to appear in Z.Phys.
Mesons and diquarks in neutral color superconducting quark matter with -equilibrium
The spectrum of meson and diquark excitations in cold color-superconducting
(2SC) quark matter is investigated under local color and electric neutrality
constraints with -equilibrium. A 2-flavored Nambu--Jona-Lasinio type
model including a baryon , color , and electric chemical
potentials is used. Two relations between coupling constants and in the
diquark- and quark-antiquark channels, correspondingly, are treated,
and . At the gapless- and at the gapped neutral color
superconductivity is realized. It is shown that color and electrical neutrality
together with -equilibrium lead to a strong mass splitting within the
pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with
non--neutral matter. It is also shown that the properties of the physical
-singlet diquark excitation in the 2SC ground state varies for
different parameterization schemes. Thus, for one finds a heavy
resonance with mass 1100 MeV in the non--neutral (gapped) case, whereas,
if neutrality is imposed, a stable diquark with mass 200 MeV
appears in the gapless 2SC phase. For , there is again a resonance (with
the mass 300 MeV) in the neutral gapped 2SC phase. Hence, the existence
of the stable massive SU(2)-singlet diquark excitation is a new peculiarity
of the gapless 2SC.Comment: 18 pages, 9 figures; version accepted for publication in PR
Positive streamers in ambient air and a N2:O2-mixture (99.8 : 0.2)
Photographs show distinct differences between positive streamers in air or in
a nitrogen-oxygen mixture (0.2% O2). The streamers in the mixture branch more
frequently, but the branches also extinguish more easily. Probably related to
that, the streamers in the mixture propagate more in a zigzag manner while they
are straighter in air. Furthermore, streamers in the mixture can become longer;
they are thinner and more intense.Comment: 2 pages, 4 figures, paper is accepted for IEEE Trans. Plasma Sci. and
scheduled to appear in June 200
Personality traits in resident and migratory warbler species.
Animals are often confronted with environmental challenges and the way in which they cope with these challenges can have important fitness consequences. There is increasing evidence that individuals differ consistently in their reaction to the environment (personality traits). However, little is known about whether different life-styles (e.g., resident or migratory) influence personality traits and if so, in what manner. We compared neophobic and exploratory behaviours, both of which play an important role in personality traits, between two closely related species, the resident Sardinian warblers and the migratory garden warblers, at two different times during the year. Neophobia was tested by placing a novel object, a mop, beside the feeding dish and measuring the latency to feed (neophobia score). Exploration was tested by offering another novel object, a tube, attached to a perch at a neutral location and measuring latency to approach and investigate the tube (exploration score). Both tests were carried out at the end of the breeding season and repeated ten months later in spring. The Sardinian warblers showed consistent behavioural reactions over time. Furthermore, neophobia and exploration scores were negatively related. The garden warblers neither behaved consistently over time nor was there a correlation between neophobia and exploration. Overall, Sardinian warblers were less neophobic and more explorative than garden warblers. The different reactivity may be due to a different frequency distribution of the individuals of the two species along a reactivity axis. It can be concluded that the Sardinian warblers have personality traits. The situation is less clear in the garden warblers. Possibly, different life-styles require different organisation of behaviours
Color superconductivity in the static Einstein Universe
We study the behavior of quark and diquark condensates in dense quark matter
under the influence of a gravitational field adopting as a simple model the
static dimensional Einstein Universe. Calculations are performed in the
framework of the extended Nambu--Jona-Lasinio model at finite temperature and
quark density on the basis of the thermodynamic potential and the gap
equations. Quark and diquark condensates as functions of the chemical potential
and temperature at different values of the curvature have been studied. Phase
portraits of the system have been constructed
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