Stability of strange quark matter: MIT bag versus Color Dielectric Model

We discuss the properties of strange matter, in particular the minimum of the energy per baryon number as a function of the strangeness fraction. We utilize both the MIT bag model and the Color Dielectric Model and compare the energy per baryon with the masses of hyperons having the corresponding strangeness fraction, which are coherently calculated within both models. We also take into account the perturbative exchange of gluons. The results obtained in the two approaches allow to discuss the stability of strangelets. While the MIT bag model and the double minimum version of the Color Dielectric Model allow the existence of strangelets, the single minimum version of the Color Dielectric Model excludes this possibility.Comment: 26 pages, 9 figure

Looking for magnetic monopoles at LHC with diphoton events

Magnetic monopoles have been a subject of interest since Dirac established the relation between the existence of monopoles and charge quantization. The intense experimental search carried thus far has not met with success. The Large Hadron Collider is reaching energies never achieved before allowing the search for exotic particles in the TeV mass range. In a continuing effort to discover these rare particles we propose here other ways to detect them. We study the observability of monopoles and monopolium, a monopole-antimonopole bound state, at the Large Hadron Collider in the $\gamma \gamma$ channel for monopole masses in the range 500-1000 GeV. We conclude that LHC is an ideal machine to discover monopoles with masses below 1 TeV at present running energies and with 5 fb$^{-1}$ of integrated luminosity.Comment: This manuscript contains information appeared in Looking for magnetic monopoles at LHC, arXiv:1104.0218 [hep-ph] and Monopolium detection at the LHC.,arXiv:1107.3684 [hep-ph] by the same authors, rewritten for joint publication in The European Physica Journal Plus. 26 pages, 22 figure

Dynamical mean-field theory of spiking neuron ensembles: response to a single spike with independent noises

Dynamics of an ensemble of $N$-unit FitzHugh-Nagumo (FN) neurons subject to white noises has been studied by using a semi-analytical dynamical mean-field (DMF) theory in which the original $2 N$-dimensional {\it stochastic} differential equations are replaced by 8-dimensional {\it deterministic} differential equations expressed in terms of moments of local and global variables. Our DMF theory, which assumes weak noises and the Gaussian distribution of state variables, goes beyond weak couplings among constituent neurons. By using the expression for the firing probability due to an applied single spike, we have discussed effects of noises, synaptic couplings and the size of the ensemble on the spike timing precision, which is shown to be improved by increasing the size of the neuron ensemble, even when there are no couplings among neurons. When the coupling is introduced, neurons in ensembles respond to an input spike with a partial synchronization. DMF theory is extended to a large cluster which can be divided into multiple sub-clusters according to their functions. A model calculation has shown that when the noise intensity is moderate, the spike propagation with a fairly precise timing is possible among noisy sub-clusters with feed-forward couplings, as in the synfire chain. Results calculated by our DMF theory are nicely compared to those obtained by direct simulations. A comparison of DMF theory with the conventional moment method is also discussed.Comment: 29 pages, 2 figures; augmented the text and added Appendice

Gravitational Coupling and Dynamical Reduction of The Cosmological Constant

We introduce a dynamical model to reduce a large cosmological constant to a sufficiently small value. The basic ingredient in this model is a distinction which has been made between the two unit systems used in cosmology and particle physics. We have used a conformal invariant gravitational model to define a particular conformal frame in terms of large scale properties of the universe. It is then argued that the contributions of mass scales in particle physics to the vacuum energy density should be considered in a different conformal frame. In this manner, a decaying mechanism is presented in which the conformal factor appears as a dynamical field and plays a key role to relax a large effective cosmological constant. Moreover, we argue that this model also provides a possible explanation for the coincidence problem.Comment: To appear in GR

Molecular and Historical Aspects of Corn Belt Dent Diversity

Tens-of-thousands of open-pollinated cultivars of corn (Zea mays L.) are being maintained in germplasm banks. Knowledge of the amount and distribution of genetic variation within and among accessions can aid end users in choosing among them. We estimated molecular genetic variation and looked for influences of pedigree, adaptation, and migration in the genetic makeup of conserved Corn-Belt Dent-related germplasm. Plants sampled from 57 accessions representing Corn-Belt Dents, Northern Flints, Southern Dents, plus 12 public inbreds, were genotyped at 20 simple sequence repeat (SSR) loci. For 47 of the accessions, between 5 and 23 plants per accession were genotyped (mean = 9.3). Mean number of alleles per locus was 6.5 overall, 3.17 within accessions, and 3.20 within pooled inbreds. Mean gene diversity was 0.53 within accessions and 0.61 within pooled inbreds. Open-pollinated accessions showed a tendency toward inbreeding (FIS = 0.09), and 85% of genetic variation was shared among them. A Fitch-Margoliash tree strongly supported the distinctiveness of flint from dent germplasm but did not otherwise reveal evidence of genetic structure. Mantel tests revealed significant correlations between genetic distance and geographical (r = 0.54, P= 0.04) or maturity zone (r = 0.33, P = 0.03) distance only if flint germplasm was included in the analyses. A significant correlation (r = 0.76, P \u3c 0.01) was found between days to pollen shed and maturity zone of accession origin. Pedigree, rather than migration or selection, has most influenced the genetic structure of the extant representatives of the open-pollinated cultivars at these SSR loci

Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV

Mid-rapidity transverse mass spectra and multiplicity densities of charged and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC. The spectra are exponential in transverse mass, with an inverse slope of about 280 MeV in central collisions. The multiplicity densities for these particles scale with the negative hadron pseudo-rapidity density. The charged kaon to pion ratios are $K^+/\pi^- = 0.161 \pm 0.002 {\rm (stat)} \pm 0.024 {\rm (syst)}$ and $K^-/\pi^- = 0.146 \pm 0.002 {\rm (stat)} \pm 0.022 {\rm (syst)}$ for the most central collisions. The $K^+/\pi^-$ ratio is lower than the same ratio observed at the SPS while the $K^-/\pi^-$ is higher than the SPS result. Both ratios are enhanced by about 50% relative to p+p and $\bar{\rm p}$+p collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl

Measurement of spin correlation in ttbar production using dilepton final states

We measure the correlation between the spin of the top quark and the spin of the anti-top quark in (ttbar -> W+ W- b bbar -> l+ nu b l- nubar bbar) final states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96 TeV, where l is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb-1 and were collected with the D0 detector at the Fermilab Tevatron collider. The correlation is extracted from the angles of the two leptons in the t and tbar rest frames, yielding a correlation strength C= 0.10^{+0.45}_{-0.45}, in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.Comment: 10 pages, 3 figures, submitted to PL

Measurement of the dijet invariant mass cross section in proton anti-proton collisions at sqrt{s} = 1.96 TeV

The inclusive dijet production double differential cross section as a function of the dijet invariant mass and of the largest absolute rapidity of the two jets with the largest transverse momentum in an event is measured in proton anti-proton collisions at sqrt{s} = 1.96 TeV using 0.7 fb^{-1} integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The measurement is performed in six rapidity regions up to a maximum rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found to be in agreement with the data.Comment: Published in Phys. Lett. B, 693, (2010), 531-538, 8 pages, 2 figures, 6 table

Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wgamma production in pp-bar collisions at sqrt{s}=1.96 TeV

We present final searches of the anomalous gammaWW and ZWW trilinear gauge boson couplings from WW and WZ production using lepton plus dijet final states and a combination with results from Wgamma, WW, and WZ production with leptonic final states. The analyzed data correspond to up to 8.6/fb of integrated luminosity collected by the D0 detector in pp-bar collisions at sqrt{s}=1.96 TeV. We set the most stringent limits at a hadron collider to date assuming two different relations between the anomalous coupling parameters Delta\kappa_\gamma, lambda, and Delta g_1^Z for a cutoff energy scale Lambda=2 TeV. The combined 68% C.L. limits are -0.057<Delta\kappa_\gamma<0.154, -0.015<lambda<0.028, and -0.008<Delta g_1^Z<0.054 for the LEP parameterization, and -0.007<Delta\kappa<0.081 and -0.017<lambda<0.028 for the equal couplings parameterization. We also present the most stringent limits of the W boson magnetic dipole and electric quadrupole moments.Comment: 10 pages, 5 figures, submitted to PL

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events

We present a measurement of the top quark pair ttbar production cross section in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1} of data collected by the DO detector at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), large missing transverse energy, and at least four jets, and extract the ttbar content of the sample based on the kinematic characteristics of the events. For a top quark mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1} (syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let