Barionski model predvidio neočekivano malu iskustvenu vektorsku stranost nukleona

Most of model considerations of the hidden nucleon strangeness, as well as some preliminary experimental evidence, led to the expectations of relatively sizeable strange vector form factors of the proton. For example, it seemed that the contribution of the fluctuating strange quark-antiquark pairs accounts for as much as one tenth of the proton\u27s magnetic moment. By the same token, baryon models which failed to produce the "vector strangeness" of the nucleon seemed disfavoured. Recently, however, more accurate measurements and more sophisticated data analysis, as well as lattice simulations, revealed that the form factors associated with the vector strangeness of the nucleon are much smaller than thought previously; in fact, due to the experimental uncertainties, the measured strange vector-current proton form factors may be consistent with zero. In the light of that, we re-asses the merit of the baryon models leading to little or no vector strangeness of the nucleon. It is done on the concrete example of the baryon model which essentially amounts to the MIT bag enriched by the diluted instanton liquid.Većina teorijskih razmatranja skrivene stranosti nukleona, kao i neki prethodni eksperimentalni podaci, potaknuli su očekivanja relativno velikih stranih vektorskih faktora oblika protona. Npr., činilo se da doprinos kolebanja parova strani kvark– antikvark iznosi čak desetinu magnetskog momenta protona. Zbog tih su stajališta bili zanemareni barionski modeli koji nisu davali “vektorsku stranost” nukleona. Međutim, nedavnija točnija mjerenja i bolje analize mjernih podataka, kao i simulacije na rešetkama, našli su da su faktori oblika povezani s vektorskom stranosti nukleona mnogo manji nego se prije mislilo. U stvari, uzevši u obzir točnost eksperimentalnih podataka, mjereni strani vektorski faktori oblika mogu biti jednaki nuli. U tom svjetlu obnavljamo razmatranje barionskih modela koji daju malu ili nultu vektorsku stranost nukleona. To smo načinili s posebnim primjerom barionskog modela koji je u biti MIT vreća obogaćena razrijeđenom tekućinom instantona

Barionski model predvidio neočekivano malu iskustvenu vektorsku stranost nukleona

Most of model considerations of the hidden nucleon strangeness, as well as some preliminary experimental evidence, led to the expectations of relatively sizeable strange vector form factors of the proton. For example, it seemed that the contribution of the fluctuating strange quark-antiquark pairs accounts for as much as one tenth of the proton\u27s magnetic moment. By the same token, baryon models which failed to produce the "vector strangeness" of the nucleon seemed disfavoured. Recently, however, more accurate measurements and more sophisticated data analysis, as well as lattice simulations, revealed that the form factors associated with the vector strangeness of the nucleon are much smaller than thought previously; in fact, due to the experimental uncertainties, the measured strange vector-current proton form factors may be consistent with zero. In the light of that, we re-asses the merit of the baryon models leading to little or no vector strangeness of the nucleon. It is done on the concrete example of the baryon model which essentially amounts to the MIT bag enriched by the diluted instanton liquid.Većina teorijskih razmatranja skrivene stranosti nukleona, kao i neki prethodni eksperimentalni podaci, potaknuli su očekivanja relativno velikih stranih vektorskih faktora oblika protona. Npr., činilo se da doprinos kolebanja parova strani kvark– antikvark iznosi čak desetinu magnetskog momenta protona. Zbog tih su stajališta bili zanemareni barionski modeli koji nisu davali “vektorsku stranost” nukleona. Međutim, nedavnija točnija mjerenja i bolje analize mjernih podataka, kao i simulacije na rešetkama, našli su da su faktori oblika povezani s vektorskom stranosti nukleona mnogo manji nego se prije mislilo. U stvari, uzevši u obzir točnost eksperimentalnih podataka, mjereni strani vektorski faktori oblika mogu biti jednaki nuli. U tom svjetlu obnavljamo razmatranje barionskih modela koji daju malu ili nultu vektorsku stranost nukleona. To smo načinili s posebnim primjerom barionskog modela koji je u biti MIT vreća obogaćena razrijeđenom tekućinom instantona

Relativistički model kvarkova

A general Lorentz-covariant quark model of mesons, whose nonrelativistic limit corresponds to Isgur-Scora-Grinstein-Wise model, is constructed. It possesses the heavy quark symmetry and can be easily applied to calculation of form factors. Besides it can be engaged in novel tasks, such a the investigation of the two photon decay of scalar mesons. Its behaviour in the infinite momentum frame and the light cone is discussed.Izveli smo poopćeni Lorentz-kovarijantni model mezona čiji nerelativistički limes odgovara Isgur-Scora-Grinstein-Wiseovom modelu. Model ima teško-kvarkovsku simetriju i može se primijeniti za računanje faktora oblika. Osim toga u ovom se modelu mogu rješavati nove zadaće kao što je dvofotonski raspad skalarnih mezona. Raspravljamo svojstva modela u sustavu beskonačnog impulsa i na svjetlosnom stošcu

Relativistički model kvarkova

A general Lorentz-covariant quark model of mesons, whose nonrelativistic limit corresponds to Isgur-Scora-Grinstein-Wise model, is constructed. It possesses the heavy quark symmetry and can be easily applied to calculation of form factors. Besides it can be engaged in novel tasks, such a the investigation of the two photon decay of scalar mesons. Its behaviour in the infinite momentum frame and the light cone is discussed.Izveli smo poopćeni Lorentz-kovarijantni model mezona čiji nerelativistički limes odgovara Isgur-Scora-Grinstein-Wiseovom modelu. Model ima teško-kvarkovsku simetriju i može se primijeniti za računanje faktora oblika. Osim toga u ovom se modelu mogu rješavati nove zadaće kao što je dvofotonski raspad skalarnih mezona. Raspravljamo svojstva modela u sustavu beskonačnog impulsa i na svjetlosnom stošcu

Novel Crossover in Coupled Spin Ladders

We report a novel crossover behavior in the long-range-ordered phase of a prototypical spin-$1/2$ Heisenberg antiferromagnetic ladder compound $\mathrm{(C_7H_{10}N)_2CuBr_4}$. The staggered order was previously evidenced from a continuous and symmetric splitting of $^{14}$N NMR spectral lines on lowering temperature below $T_c\simeq 330$ mK, with a saturation towards $\simeq 150$ mK. Unexpectedly, the split lines begin to further separate away below $T^*\sim 100$ mK while the line width and shape remain completely invariable. This crossover behavior is further corroborated by the NMR relaxation rate $T_1^{-1}$ measurements. A very strong suppression reflecting the ordering, $T_1^{-1}\sim T^{5.5}$, observed above $T^*$, is replaced by $T_1^{-1}\sim T$ below $T^*$. These original NMR features are indicative of unconventional nature of the crossover, which may arise from a unique arrangement of the ladders into a spatially anisotropic and frustrated coupling network.Comment: 5 pages, 3 figure

η\eta and η′\eta' mesons in the Dyson-Schwinger approach at finite temperature

We study the temperature dependence of the pseudoscalar meson properties in a relativistic bound-state approach exhibiting the chiral behavior mandated by QCD. Concretely, we adopt the Dyson-Schwinger approach with a rank-2 separable model interaction. After extending the model to the strange sector and fixing its parameters at zero temperature, T=0, we study the T-dependence of the masses and decay constants of all ground-state mesons in the pseudoscalar nonet. Of chief interest are $\eta$ and $\eta^\prime$. The influence of the QCD axial anomaly on them is successfully obtained through the Witten-Veneziano relation at T=0. The same approach is then extended to T>0, using lattice QCD results for the topological susceptibility. The most conspicuous finding is an increase of the $\eta^\prime$ mass around the chiral restoration temperature $T_{\rm Ch}$, which would suggest a suppression of $\eta^\prime$ production in relativistic heavy-ion collisions. The increase of the $\eta^\prime$ mass may also indicate that the extension of the Witten-Veneziano relation to finite temperatures becomes unreliable around and above $T_{\rm Ch}$. Possibilities of an improved treatment are discussed.Comment: 13 pages, 15 figure

Distribution and morphological variations of invasive macrophytes Elodea nuttallii (Planch.) H. St. John and Elodea canadensis Michx in Croatia

The invasive species Elodea nuttallii was recorded for the first time in the Croatian flora in 2006, in the drainage channels of Kopački rit (Baranja). After its establishment, E. nuttallii begins to spread to the eastern and northern part of the drainage channel network from 2006–2009. High water levels are responsible for the linear spreading direction of E. nuttallii, E. nuttallii and E. canadensis show a wide range of morphological variation, which is characteristic of successful invaders. To show morphological variations of two Elodea species, the most impor tant characters indicated in the literature were measured on 24 fresh collected samples from the seven sites in Croatia. In spite of some overlap in leaf length and width between the two Elodea species, the differences of all morphological traits except internode length are statistically significant. In E. nuttallii leaf width, length and internode length show a higher morphological variability as a result of the higher adaptive strategy to environmental parameters. The most reliable morphological characters distinguishing E. nuttallii and E. canadensis are leaf width 0.5 mm below the tip and the angle at the apex. E. nuttallii can be expected to spread to other areas of Croatia

Width of the QCD transition in a Polyakov-loop DSE model

We consider the pseudocritical temperatures for the chiral and deconfinement transitions within a Polyakov-loop Dyson-Schwinger equation approach which employs a nonlocal rank-2 separable model for the effective gluon propagator. These pseudocritical temperatures differ by a factor of two when the quark and gluon sectors are considered separately, but get synchronized and become coincident when their coupling is switched on. The coupling of the Polyakov-loop to the chiral quark dynamics narrows the temperature region of the QCD transition in which chiral symmetry and deconfinement is established. We investigate the effect of rescaling the parameter T_0 in the Polyakov-loop potential on the QCD transition for both the logarithmic and polynomial forms of the potential. While the critical temperatures vary in a similar way, the width of the transition is stronger affected for the logarithmic potential. For this potential the character of the transition changes from crossover to a first order one when T_0 < 210 MeV, but it remains crossover in the whole range of relevant T_0 values for the polynomial form.Comment: 10 pages, 6 figures, results for polynomial form of Polyakov-loop potential included, references added, final version to appear in Phys. Rev.