15,259,363 research outputs found
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 () 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 and . 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
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. 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
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