Some consequences of a noncommutative space-time structure

The existence of a fundamental length (or fundamental time) has been conjecture in many contexts. Here one discusses some consequences of a fundamental constant of this type, which emerges as a consequence of deformation-stability considerations leading to a non-commutative space-time structure. This mathematically well defined structure is sufficiently constrained to allow for unambiguous experimental predictions. In particular one discusses the phase-space volume modifications and their relevance for the calculation of the GZK sphere. Corrections to the spectrum of the Coulomb problemb are also computed.Comment: 17 pages Latex, 3 figure

Low temperature magnetic phase diagram of the cubic non-Fermi liquid system CeIn_(3-x)Sn_x

In this paper we report a comprehensive study of the magnetic susceptibility (\chi), resistivity (\rho), and specific heat (C_P), down to 0.5 K of the cubic CeIn_(3-x)Sn_x alloy. The ground state of this system evolves from antiferromagnetic (AF) in CeIn_3(T_N=10.2 K) to intermediate-valent in CeSn_3, and represents the first example of a Ce-lattice cubic non-Fermi liquid (NFL) system where T_N(x) can be traced down to T=0 over more than a decade of temperature. Our results indicate that the disappearance of the AF state occurs near x_c ~ 0.7, although already at x ~ 0.4 significant modifications of the magnetic ground state are observed. Between these concentrations, clear NFL signatures are observed, such as \rho(T)\approx \rho_0 + A T^n (with n<1.5) and C_P(T)\propto -T ln(T) dependencies. Within the ordered phase a first order phase transition occurs for 0.25 < x < 0.5. With larger Sn doping, different weak \rho(T) dependencies are observed at low temperatures between x=1 and x=3 while C_P/T shows only a weak temperature dependence.Comment: 7 pages, 7 figures. Accepted in Eur. J. Phys.

Final state interaction effects in semi-inclusive DIS off the deuteron

The effects of the final state interaction (FSI) in semi-exclusive deep-inelastic scattering of electrons off the deuteron are analyzed paying particular attention to two extreme kinematical regions: i) the one where FSI effects are minimized, so that the quark distribution of bound nucleons could be investigated, and ii) the one where the re-interaction of the produced hadrons with the spectator nucleon is maximized, which would allow one to study the mechanism of hadronization of highly virtual quark. It is demonstrated that when the recoiling spectator nucleon is detected in the backward hemisphere with low momentum the effects from FSI are negligible, whereas at large transverse momenta of the spectator the FSI effects are rather large. Numerical estimates show that the FSI corrections are sensitive to the theoretical models of the hadronization mechanism.Comment: 18 pages 6 figures A draft of the paper was erroneously sent instead of the paper itsel

Use of W-Boson Longitudinal-Transverse Interference in Top Quark Spin-Correlation Functions: II

This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of top-antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production contributions are included for the charged-lepton-plus-jets reaction p p or p bar{p} --> t bar{t} --> (W^+ b)(W^- bar{b}) --> (l^{+} nu b)(W^- bar{b}). There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of, or for measurement of a possible non-trivial phase between the two dominant helicity amplitudes for t --> W^{+} b decay. There is an analogous function and tests for bar{t} --> W^{-} bar{b} decay. This signature requires use of the (t bar{t}) c.m.-energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar-angle of W-boson emission in the anti-top (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude phase convention of Jacob & Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal-transverse interference effect.Comment: Continuation of hep-ph/0506240 to include gluon-production contribution; 3 "postscript" figures. Equation numbers as in published-on-line EPJ

Transport and Localisation in the Presence of Strong Structural and Spin Disorder

We study a tight binding model including both on site disorder and coupling of the electrons to randomly oriented magnetic moments. The transport properties are calculated via the Kubo-Greenwood scheme, using the exact eigenstates of the disordered system and large system size extrapolation of the low frequency optical conductivity. We first benchmark our method in the model with only structural disorder and then use it to map out the transport regimes and metal- insulator transitions in problems involving (i) scattering from random magnetic moments, and (ii) the combined effect of structural disorder and magnetic scattering. We completely map out the dependence of the d.c conductivity on electron density (n) the structural disorder (\Delta) and the magnetic coupling (J'), and locate the insulator-metal phase boundary in the space of n-\Delta-J'. These results serve as a reference for understanding transport in systems ranging from magnetic semiconductors to double exchange `colossal magnetoresistance' systems. A brief version of this study appears in our earlier paper Europhys. Lett. vol 65, 75 (2004).Comment: 14 pages revtex. Final version, to appear in EPJ

Electric dipole moments of charged leptons in the split fermion scenario in the two Higgs doublet model

We predict the charged lepton electric dipole moments in the split fermion scenario in the framework of the two Higgs doublet model. We observe that the numerical value of the muon (tau) electric dipole moment is at the order of the magnitude of $10^{-22} (e-cm)$ ($10^{-20} (e-cm)$) and there is an enhancement in the case of two extra dimensions, especially for the tau lepton electric dipole moment.Comment: 17 pages, 5 figure

Generalized parton distributions from nucleon form factor data

We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit to experimental data for the Dirac, Pauli and axial form factors of the nucleon allows us to discuss quantitatively the interplay between longitudinal and transverse partonic degrees of freedom in the nucleon ("nucleon tomography"). In particular we obtain the transverse distribution of valence quarks at given momentum fraction x. We calculate various moments of the distributions, including the form factors that appear in the handbag approximation to wide-angle Compton scattering. This allows us to estimate the minimal momentum transfer required for reliable predictions in that approach to be around |t|~3 GeV^2. We also evaluate the valence contributions to the energy-momentum form factors entering Ji's sum rule.Comment: 69 pages, 36 figures. v2: small improvements in text and figures; references adde

T-odd Correlations in the Decay of Scalar Fermions

We define a CP sensitive asymmetry in the sfermion decays \ti f \to f \ti\chi^0_j \ell \bar \ell, f \ti\chi^0_j q \bar q, based on triple product correlations between the momenta of the outgoing fermions. We study this asymmetry in the MSSM with complex parameters. We show that the asymmetry is sensitive to the phases of the parameters $\mu$ and $M_1$. The leading contribution stems from the decay chain \ti f\to f \ti\chi^0_j\to f \ti\chi^0_1 Z\to f \ti\chi^0_1 \ell \bar \ell (f \ti\chi^0_1 q \bar q), for which we obtain analytic formulae for the amplitude squared. The asymmetry can go up to 3% for \ti f\to f \ti\chi^0_1 \ell \bar \ell, and up to 20% for \ti f\to f \ti\chi^0_1 q \bar q. We also estimate the rates necessary to measure the asymmetry.Comment: 18 pages, 5 figures, 2 tables; comments and references added; two tables added; version to appear in Eur. Phys.

Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|$\eta$|<0.8) and transverse momentum range 0.2< $p_{\rm T}$< 5.0 GeV/$c$. The elliptic flow signal v$_2$, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is 0.087 $\pm$ 0.002 (stat) $\pm$ 0.004 (syst) in the 40-50% centrality class. The differential elliptic flow v$_2(p_{\rm T})$ reaches a maximum of 0.2 near $p_{\rm T}$ = 3 GeV/$c$. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/389