2,146 research outputs found
Mass Dependent Evolution and the Light Gluino Existence
There is an intriguing discrepancy between \alpha_s(M_Z) values measured
directly at the CERN -factory and low-energy (at few GeV) measurements
transformed to by a massless QCD \alpha_s(Q) evolution relation.
There exists an attempt to reconcile this discrepancy by introducing a light
gluino \gl in the MSSM.
We study in detail the influence of heavy thresholds on \alpha_s(Q)
evolution. First, we consruct the "exact" explicit solution to the
mass-dependent two-loop RG equation for the running \alpha_s(Q). This solution
describes heavy thresholds smoothly. Second, we use this solution to
recalculate anew \alpha_s(M_Z) values corresponding to "low-energy" input data.
Our analysis demonstrates that using {\it mass-dependent RG procedure}
generally produces corrections of two types: Asymptotic correction due to
effective shift of threshold position; Local threshold correction only for the
case when input experiment lies in the close vicinity of heavy particle
threshold: .
Both effects result in the effective shift of the \asmz values of the order
of . However, the second one could be enhanced when the gluino mass is
close to a heavy quark mass. For such a case the sum effect could be important
for the discussion of the light gluino existence as it further changes the
\gl mass.Comment: 13, Late
Rigorous Real-Time Feynman Path Integral for Vector Potentials
we will show the existence and uniqueness of a real-time, time-sliced Feynman
path integral for quantum systems with vector potential. Our formulation of the
path integral will be derived on the transition probability amplitude via
improper Riemann integrals. Our formulation will hold for vector potential
Hamiltonian for which its potential and vector potential each carries at most a
finite number of singularities and discontinuities
Ruelle-Perron-Frobenius spectrum for Anosov maps
We extend a number of results from one dimensional dynamics based on spectral
properties of the Ruelle-Perron-Frobenius transfer operator to Anosov
diffeomorphisms on compact manifolds. This allows to develop a direct operator
approach to study ergodic properties of these maps. In particular, we show that
it is possible to define Banach spaces on which the transfer operator is
quasicompact. (Information on the existence of an SRB measure, its smoothness
properties and statistical properties readily follow from such a result.) In
dimension we show that the transfer operator associated to smooth random
perturbations of the map is close, in a proper sense, to the unperturbed
transfer operator. This allows to obtain easily very strong spectral stability
results, which in turn imply spectral stability results for smooth
deterministic perturbations as well. Finally, we are able to implement an Ulam
type finite rank approximation scheme thus reducing the study of the spectral
properties of the transfer operator to a finite dimensional problem.Comment: 58 pages, LaTe
Spectroscopy of Na: Bridging the two-proton radioactivity of Mg
The unbound nucleus Na, the intermediate nucleus in the two-proton
radioactivity of Mg, was studied by the measurement of the resonant
elastic scattering reaction Ne(p,Ne)p performed at 4 A.MeV.
Spectroscopic properties of the low-lying states were obtained in a R-matrix
analysis of the excitation function. Using these new results, we show that the
lifetime of the Mg radioactivity can be understood assuming a sequential
emission of two protons via low energy tails of Na resonances
Multiple-Point and Multiple-Time Correlations Functions in a Hard-Sphere Fluid
A recent mode coupling theory of higher-order correlation functions is tested
on a simple hard-sphere fluid system at intermediate densities. Multi-point and
multi-time correlation functions of the densities of conserved variables are
calculated in the hydrodynamic limit and compared to results obtained from
event-based molecular dynamics simulations. It is demonstrated that the mode
coupling theory results are in excellent agreement with the simulation results
provided that dissipative couplings are included in the vertices appearing in
the theory. In contrast, simplified mode coupling theories in which the
densities obey Gaussian statistics neglect important contributions to both the
multi-point and multi-time correlation functions on all time scales.Comment: Second one in a sequence of two (in the first, the formalism was
developed). 12 pages REVTeX. 5 figures (eps). Submitted to Phys.Rev.
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Challenges in QCD matter physics --The scientific programme of the Compressed Baryonic Matter experiment at FAIR
Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sNN= 2.7--4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (μB> 500 MeV), effects of chiral symmetry, and the equation of state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2024, in the context of the worldwide efforts to explore high-density QCD matter
Proton Drip-Line Calculations and the Rp-process
One-proton and two-proton separation energies are calculated for proton-rich
nuclei in the region . The method is based on Skyrme Hartree-Fock
calculations of Coulomb displacement energies of mirror nuclei in combination
with the experimental masses of the neutron-rich nuclei. The implications for
the proton drip line and the astrophysical rp-process are discussed. This is
done within the framework of a detailed analysis of the sensitivity of rp
process calculations in type I X-ray burst models on nuclear masses. We find
that the remaining mass uncertainties, in particular for some nuclei with
, still lead to large uncertainties in calculations of X-ray burst light
curves. Further experimental or theoretical improvements of nuclear mass data
are necessary before observed X-ray burst light curves can be used to obtain
quantitative constraints on ignition conditions and neutron star properties. We
identify a list of nuclei for which improved mass data would be most important.Comment: 20 pages, 9 figures, 2 table
Non-stationary distributed source approximation: an alternative to improve localization procedures
Localization of the generators of the scalp measured electrical activity is particularly difficult when a large number of brain regions are simultaneously active. In this study, we describe an approach to automatically isolate scalp potential maps, which are simple enough to expect reasonable results after applying a distributed source localization procedure. The isolation technique is based on the time-frequency decomposition of the scalp-measured data by means of a time-frequency representation. The basic rationale behind the approach is that neural generators synchronize during short time periods over given frequency bands for the codification of information and its transmission. Consequently potential patterns specific for certain time-frequency pairs should be simpler than those appearing at single times but for all frequencies. The method generalizes the FFT approximation to the case of distributed source models with non-stationary time behavior. In summary, the non-stationary distributed source approximation aims to facilitate the localization of distributed source patterns acting at specific time and frequencies for non-stationary data such as epileptic seizures and single trial event related potentials. The merits of this approach are illustrated here in the analysis of synthetic data as well as in the localization of the epileptogenic area at seizure onset in patients. It is shown that time and frequency at seizure onset can be precisely detected in the time-frequency domain and those localization results are stable over seizures. The results suggest that the method could also be applied to localize generators in single trial evoked responses or spontaneous activity
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