Pomeron with a running coupling constant in the nucleus

The running coupling is introduced into the equation for propagation of the pomeron in the nucleus via the bootstrap relation. The resulting equation coincides with the one obtained in the color dipole formalism by summing contributions from quark–antiquark loops, with a general choice of the regularization scheme.     

Evolution of the gluon density in x with a running coupling constant

We describe the calculation of the evolution of the gluon density in from an initial value to smaller values, up to in the hard pomeron formalism with a running coupling introduced on the basis of the bootstrap equation. The obtained gluon density is used to calculate the singlet part of the proton structure function. Comparison with experiment and the results following from the fixed coupling evolutio n is made. Received: 10 June 1997 / Revised version: 20 August 1997 / Published online: 24 April 1998     

The effect of quark masses on the running of the QCD coupling constant

The presence of thresholds for finite quark masses alters the behavior of the QCD coupling constant. While the alterations are small they can have significant influence on the determination of the scale parameter Λ. Part of the discrepancy between recent highQ ² determinations of Λ and older lowQ ² determinations can be attributed to charm and bottom thresholds. We present simple, analytic expressions for the mass dependence of α(Q ²) and exploit these to discuss Λ determinations, scale breaking and the phenomenon of temporary freedom when more than 17 quark flavors exist.     

Non-perturbative determination of the running coupling constant in quenched SU (2)

Through a finite-size renormalization group technique we calculate the running coupling constant for quenched SU(2) with a few percent error over a range of energy varying by a factor thirty. The definition is based on ratio of correlations of Polyakov loops with twisted boundary conditions. The extrapolation to the continuum limit is governed by corrections due to lattice artifacts which appear to be rather smooth and proportional to the square of the lattice spacing.     

Quark-pion coupling constant in a chiral quark model

Incorporating chiral-symmetry to the potential model of quarks with confining potentialU(r)=1/2 (1 +γ°)ar ² with m _q =10 MeV anda=2.273 fm⁻³ that gives a reasonable quark-core contribution to μ _p , 〈r ² 〉 _p ^1/2 andg _A , the quark-pion coupling constant for quarks in a nucleon is estimated.G _qqπ ² /4π obtained between 0.4 and 0.5 is consistent with those extracted from experimental vector meson decay-width ratios by Suzuki and Bhaduri. The nucleon-pion coupling constantG _NNπ ² /4π comes out to be of the order of 13.1 in reasonable agreement with the experimental value.     

Holographic fermions with running chemical potential and dipole coupling

We explore the properties of the holographic fermions in extremal R-charged black hole background with a running chemical potential, as well as the dipole coupling between fermions and the gauge field in the bulk. We find that although the running chemical potential effect the location of the Fermi surface, it does not change the type of fermions. We also study the onset of the Fermi gap and the gap effected by running chemical potential and the dipole coupling. The spectral function in the limit ω→0$\omega \to 0$ and the existence of the Fermi liquid are also investigated. The running chemical potential and the dipole coupling altogether can make a non-Fermi liquid become the Landau–Fermi type.     

Properties of quark matter in a new quasiparticle model with QCD running coupling

The running of the QCD coupling in the effective mass causes thermodynamic inconsistency problem in the conventional quasiparticle model. We provide a novel treatment which removes the inconsistency by an effective bag constant. The chemical potential dependence of the renormalization subtraction point is constrained by the Cauchy condition in the chemical potential space. The stability and microscopic properties of strange quark matter are then studied within the completely self-consistent quasiparticle model, and the obtained equation of state of quark matter is applied to the investigation of strange stars. It is found that our improved model can describe well compact stars with mass about two times the solar mass, which indicates that such massive compact stars could be strange stars.     

The running coupling at finite temperature

We propose the ensemble averaged running coupling as the meaningful measure of the coupling strength of an equilibrium gas and consider its scaling behaviour. We show that the high temperature limit of the average coupling is obtained by keeping the temperature to the renormalization point ratio,T/μ, fixed. In hot QCD gas this implies asymptotic freedom and a beta function which is independent ofT up to two loops. In the MOM scheme a minimal sensitivity to temperature is obtained with the choice μ=2.6T.     

The pion nucleon coupling constant

The latest elastic scattering data are re-analysed to determine the coupling constant g_c of the charged pion, using the dispersion relation for the invariant amplitude B^{(+ )}. Depending on the choice of data-base, values to 13.65 are obtained with errors of . The mass difference between charge states of is MeV, close to twice the mass difference between neutron and proton. The difference in widths on resonance is MeV. One may account for a width difference of 4.5 MeV from phase space for decays and the extra channel .Received: 21 January 2004, Published online: 3 March 2004     

Cosmological constant and quantum gravitational corrections to the running fine structure constant

The quantum gravitational contribution to the renormalization group behavior of the electric charge in Einstein-Maxwell theory with a cosmological constant is considered. Quantum gravity is shown to lead to a contribution to the running charge not present when the cosmological constant vanishes. This reopens the possibility, suggested by Robinson and Wilczek, of altering the scaling behavior of gauge theories at high energies although our result differs. We show the possibility of an ultraviolet fixed point that is linked directly to the cosmological constant.     

Non-linear coupling in the dark sector as a running vacuum model

In this work we study a phenomenological non-gravitational interaction between dark matter and dark energy. The scenario studied in this work extends the usual interaction model proportional to the derivative of the dark component density adding to the coupling a non-linear term of the form \(Q = \rho '/3(\alpha + \beta \rho _{Dark})\) This dark sector interaction model could be interpreted as a particular case of a running vacuum model of the type \(\Lambda (H) = n_0 + n_1 H^2 + n_2 H^4\) in which the vacuum decays into dark matter. For a flat FRW Universe filled with dark energy, dark matter and decoupled baryonic matter and radiation we calculate the energy density evolution equations of the dark sector and solve them. The different sign combinations of the two parameters of the model show clear qualitative different cosmological scenarios, from basic cosmological insights we discard some of them. The linear scalar perturbation equations of the dark matter were calculated. Using the CAMB code we calculate the CMB and matter power spectra for some values of the parameters \(\alpha \) and \(\beta \) and compare it with \(\Lambda \)CDM. The model modify mainly the lower multipoles of the CMB power spectrum remaining almost the same the high ones. The matter power spectrum for low wave numbers is not modified by the interaction but after the maximum it is clearly different. Using observational data from Planck, and various galaxy surveys we obtain the constraints of the parameters, the best fit values obtained are the combinations \(\alpha = (3.7 \pm 7 )\times 10^{-4} \), \(-\,(1.5\times 10^{-5}\, \mathrm{eV}^{-1})^{4} \ll \beta < (0.07\,\mathrm{eV}^{-1})^4\).     

The NΛK coupling constant

A dispersion relation analysis has been performed using the real parts of the K^±p forward scattering amplitudes measured over the incident momentum region from 1 to 3 GeV/c by the electronics experiment of the preceding letter. Two possible values are found for the NΛK coupling constant. One of them is in very good agreement with the symmetry theory predictions.     

Jet quenching with running coupling including radiative and collisional energy losses

We calculate the nuclear modification factor for RHIC and LHC conditions accounting for the radiative and collisional parton energy loss with the running coupling constant. We find that the RHIC data can be explained both in the scenario with the chemically equilibrium quark-gluon plasma and purely gluonic plasma with slightly different thermal suppression of the coupling constant. The role of the parton energy gain due to gluon absorption is also investigated. Our results show that the energy gain gives negligible effect. The article is published in the original.     

Determination of the axial-vector weak coupling constant with ultracold neutrons

A precise measurement of the neutron decay β asymmetry A? has been carried out using polarized ultracold neutrons from the pulsed spallation ultracold neutron source at the Los Alamos Neutron Science Center. Combining data obtained in 2008 and 2009, we report A? = -0.119?66±0.000?89{-0.001?40}{+0.001?23}, from which we determine the ratio of the axial-vector to vector weak coupling of the nucleon g{A}/g{V}=-1.275?90{-0.004?45}{+0.004?09}.     

The quasi-magnetic-hysteresis behavior of polydisperse ferrofluids with small coupling constant

The magnetization behaviors of ferrofluids based on γ-Fe₂O₃/Ni₂O₃ composite nanoparticles of size about 11 nm have been investigated. The dipole coupling constant λ of these particles is so small (0.43) that they cannot form aggregates through magnetic interaction alone. Experimental results have shown that for a polydisperse ferrofluid with a particle volume fraction of ?_V=2.4%, the magnetization curve exhibits quasi-magnetic-hysteresis behavior, i.e., the demagnetization curve lies above the magnetization curve in a high field. However, for a more dilute γ-Fe₂O₃/Ni₂O₃ ferrofluid with ?_V=0.94%, the magnetization curve does not show such behavior. According to the bidisperse model for polydisperse ferrofluids, these magnetization behaviors may be attributed to field-induced effects of self-assembled pre-existing chain-like aggregates. For such pre-existing chain-like aggregates, the orientation of the moments inside the particles is not co-linear, so that during the magnetization and demagnetization processes, their apparent magnetizations at the high-field limit are different. As a consequence, the magnetization curve of the ferrofluid with ?_V=2.4% displays quasi-magnetic-hysteresis.     

Asymptotics of QCD traveling waves with fluctuations and running coupling effects

Extending the Balitsky–Kovchegov (BK) equation independently to running coupling or to fluctuation effects due to pomeron loops is known to lead in both cases to qualitative changes of the traveling-wave asymptotic solutions. In this paper we study the extension of the forward BK equation, including both running coupling and fluctuations effects, extending the method developed for the fixed coupling case [E. Brunet, B. Derrida, A.H. Mueller, S. Munier, Phys. Rev. E 73 (2006) 056126, cond-mat/0512021]. We derive the exact asymptotic behavior in rapidity of the probabilistic distribution of the saturation scale.