Effective Functional Form of Regge Trajectories

We present theoretical arguments and strong phenomenological evidence that hadronic Regge trajectories are essentially nonlinear and can be well approximated, for phenomenological purposes, by a specific square-root form.Comment: 29 pages, LaTeX. Published versio

Delay times and reflection in chaotic cavities with absorption

Absorption yields an additional exponential decay in open quantum systems which can be described by shifting the (scattering) energy E along the imaginary axis, E+i\hbar/2\tau_{a}. Using the random matrix approach, we calculate analytically the distribution of proper delay times (eigenvalues of the time-delay matrix) in chaotic systems with broken time-reversal symmetry that is valid for an arbitrary number of generally nonequivalent channels and an arbitrary absorption rate 1/\tau_{a}. The relation between the average delay time and the ``norm-leakage'' decay function is found. Fluctuations above the average at large values of delay times are strongly suppressed by absorption. The relation of the time-delay matrix to the reflection matrix S^{\dagger}S is established at arbitrary absorption that gives us the distribution of reflection eigenvalues. The particular case of single-channel scattering is explicitly considered in detail.Comment: 5 pages, 3 figures; final version to appear in PRE (relation to reflection extended, new material with Fig.3 added, experiment cond-mat/0305090 discussed

Effective Action for QED with Fermion Self-Interaction in D=2 and D=3 Dimensions

In this work we discuss the effect of the quartic fermion self-interaction of Thirring type in QED in D=2 and D=3 dimensions. This is done through the computation of the effective action up to quadratic terms in the photon field. We analyze the corresponding nonlocal photon propagators nonperturbatively in % \frac{k}{m}, where k is the photon momentum and m the fermion mass. The poles of the propagators were determined numerically by using the Mathematica software. In D=2 there is always a massless pole whereas for strong enough Thirring coupling a massive pole may appear . For D=3 there are three regions in parameters space. We may have one or two massive poles or even no pole at all. The inter-quark static potential is computed analytically in D=2. We notice that the Thirring interaction contributes with a screening term to the confining linear potential of massive QED_{2}. In D=3 the static potential must be calculated numerically. The screening nature of the massive QED$_{3}$ prevails at any distance, indicating that this is a universal feature of % D=3 electromagnetic interaction. Our results become exact for an infinite number of fermion flavors.Comment: Latex, 13 pages, 3 figure

Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV

We present a search for the production of neutral Higgs bosons decaying into tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the 95% C.L. on the product of production cross section and branching ratio for a scalar resonance decaying into tautau pairs, and we then interpret these limits as limits on the production of Higgs bosons in the minimal supersymmetric standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL

Measurement of three-jet differential cross sections d sigma-3jet / d M-3jet in p anti-p collisions at sqrt(s)=1.96 TeV

We present the first measurement of the inclusive three-jet differential cross section as a function of the invariant mass of the three jets with the largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96 TeV. The measurement is made in different rapidity regions and for different jet transverse momentum requirements and is based on a data set corresponding to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at the Fermilab Tevatron Collider. The results are used to test the three-jet matrix elements in perturbative QCD calculations at next-to-leading order in the strong coupling constant. The data allow discrimination between parametrizations of the parton distribution functions of the proton.Comment: 10 pages, 4 figures, 2 tables, submitted to Phys. Lett. B, corrected chi2 values for NNPD

Measurements of inclusive W+jets production rates as a function of jet transverse momentum in ppbar collisions at sqrt{s}=1.96 TeV

This Letter describes measurements of inclusive W (--> e nu) + n jet cross sections (n = 1-4), presented as total inclusive cross sections and differentially in the nth jet transverse momentum. The measurements are made using data corresponding to an integrated luminosity of 4.2 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider, and achieve considerably smaller uncertainties on W +jets production cross sections than previous measurements. The measurements are compared to next-to-leading order perturbative QCD (pQCD) calculations in the n =1-3 jet multiplicity bins and to leading order pQCD calculations in the 4-jet bin. The measurements are generally in agreement with pQCD predictions, although certain regions of phase space are identified where the calculations could be improved

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