Bulk and local magnetic susceptibility in CeAl2 and CeB6

A comprehensive and high-precision magnetoresistance (MR) Δρ/ρ(H,T)$\mathrm{\Delta }\rho /\rho (H,T)$ and magnetization M(H,T) measurements have been carried out for two well known and archetypal magnetic strongly correlated electron systems—CeAl₂ and CeB₆. It was shown that the main Brillouin-type component of MR in these magnetic heavy fermion compounds can be consistently interpreted in the frameworks of a simple relation between resistivity and magnetization—Δρ/ρ∼M²$\mathrm{\Delta }\rho /\rho \sim M^2$ obtained by Yosida [Phys. Rev. 107 (1957) 396]. A local magnetic susceptibility _χloc(T,H)=(1/H^*(d(Δρ/ρ)/dH))^1/2${\chi }_{\mathrm{loc}}(T,H)=(1/H^{*}(\mathrm{d}(\mathrm{\Delta }\rho /\rho )/\mathrm{d}H){)}^{1/2}$ was deduced directly from this part of MR and compared in details with the data of bulk susceptibility χ(T,H) measurements. Two additional contributions to MR have been also deduced for CeAl₂ ((i) linear (∼H) and (ii) nanoscale ferromagnetic components) and applied for a characterization of spin polarons in this magnetic material. The dependencies χ_loc(T,H) and χ(T,H) obtained in this study for CeB₆ and CeAl₂ allow us to analyze the H–T magnetic phase diagram in these magnetic heavy fermion compounds.     

Conductance oscillations in a mesoscopic ring threaded by a harmonically time-dependent magnetic flux

We consider a microscopic model for a one-dimensional ring of non-interacting electrons threaded by a magnetic flux of the form Φ(t)=Φ₀+Φ₁cos(Ω₀t)$\Phi (t)={\Phi }_0+{\Phi }_1\cos ({\Omega }_{0}t)$. The ring is attached to two reservoirs at which a bias voltage is applied. We focus on small amplitudes of Φ₁${\Phi }_1$, and we analyze the behavior of the conductance as a function of Φ₀${\Phi }_0$. We solve the problem by means of non-equilibrium Green function techniques.     

On phantom thermodynamics

The thermodynamic properties of dark energy fluids described by an equation of state parameter ω=p/ρ$\omega =p/\rho$ are rediscussed in the context of FRW type geometries. Contrarily to previous claims, it is argued here that the phantom regime ω<−1$\omega <-1$ is not physically possible since that both the temperature and the entropy of every physical fluids must be always positive definite. This means that one cannot appeal to negative temperature in order to save the phantom dark energy hypothesis as has been recently done in the literature. Such a result remains true as long as the chemical potential is zero. However, if the phantom fluid is endowed with a non-null chemical potential, the phantom field hypothesis becomes thermodynamically consistent, that is, there are macroscopic equilibrium states with T>0$T>0$ and S>0$S>0$ in the course of the Universe expansion.     

Symmetry energy from elliptic flow in Au + Au

The elliptic-flow ratio of neutrons with respect to protons or light complex particles in reactions of neutron-rich systems at relativistic energies is proposed as an observable sensitive to the strength of the symmetry term in the equation of state at supra-normal densities. The results obtained from the existing FOPI/LAND data for ¹⁹⁷Au + ¹⁹⁷Au collisions at 400 MeV/nucleon in comparison with the UrQMD model favor a moderately soft symmetry term with a density dependence of the potential term proportional to γ(ρ/ρ₀)${(\rho /{\rho }_0)}^{\gamma }$ with γ=0.9±0.4$\gamma =0.9\pm 0.4$.     

Quark mass dependence of the pion vector form factor

We examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the ρ   to pions, g_ρππ$g_{\rho \pi \pi }$, is largely independent of the quark mass while the quark mass dependence of the ρ mass is given by recent lattice data. By employing the Omnès representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the ρππ   coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for physical values for the quark masses, namely 〈r⁴〉=0.73±0.09 fm⁴$〈r^4〉=0.73\pm 0.09{\text{fm}}^4$ or equivalently cV=4.00±0.50 GeV−4$c_V=4.00\pm 0.50{\text{GeV}}^{-4}$.     

The fate of conformal symmetry in the non-linear Schrödinger theory

The free Schrödinger theory in d   space dimensions is a non-relativistic conformal field theory. The interacting non-linear theory preserves this symmetry in specific numbers of dimensions at the classical (tree) level. This holds in particular for the |Φ|⁴${|\Phi |}^4$-theory in d=2$d=2$. We compute the full quantum corrections to the 1PI 4-point function in d=2−?$d=2-\mathrm{?}$ dimensions and find a non-trivial β  -function completely given by the 1-loop result. We exhibit an explicit Ward-identity showing that scale-invariance is broken in the limit d=2$d=2$ by an anomalous contribution proportional to the β-function.     

On phantom thermodynamics with negative temperature

We discuss the thermodynamic properties of the Friedmann–Robertson–Walker universe with dark energy fluids labelled by ω=p/ρ<−1/3$\omega =p/\rho <-1/3$. Using the integrability condition, we show that the phantom phase of ω<−1$\omega <-1$ can still be thermodynamically allowed even when the temperature takes on negative values because in that case, there exists at least a condition of keeping physical values for p and ρ.     

Holographic dark energy interacting with dark matter in a closed Universe

A cosmological model of an holographic dark energy interacting with dark matter throughout a decaying term of the form Q=3(λ₁ρDE+λ₂ρm)H$Q=3({\lambda }_1{\rho }_{\mathrm{DE}}+{\lambda }_2{\rho }_m)H$ is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenario, without any reference to a specific equation of state for the dark energy. The behavior of equation of state for dark energy is also discussed.     

Transition between SU(4) and SU(2) Kondo effect

Motivated by experiments in nanoscopic systems, we study a generalized Anderson, which consist of two spin degenerate doublets hybridized to a singlet by the promotion of an electron to two conduction bands, as a function of the energy separation δ$\delta$ between both doublets. For δ=0$\delta =0$ or very large, the model is equivalent to a one-level SU(N$N$) Anderson model, with N=4$N=4$ and 2 respectively. We study the evolution of the spectral density for both doublets (ρ_1σ(ω)${\rho }_{1\sigma }(\omega )$ and ρ_2σ(ω)${\rho }_{2\sigma }(\omega )$) and their width in the Kondo limit as δ$\delta$ is varied, using the non-crossing approximation (NCA). As δ$\delta$ increases, the peak at the Fermi energy in the spectral density (Kondo peak) splits and the density of the doublet of higher energy ρ_2σ(ω)${\rho }_{2\sigma }(\omega )$ shifts above the Ferrmi energy. The Kondo temperature T_K (determined by the half-width at half maximum of the Kondo peak in density of the doublet of lower energy ρ_1σ(ω)${\rho }_{1\sigma }(\omega )$) decreases dramatically. The variation of T_K with δ$\delta$ is reproduced by a simple variational calculation.     

Systematic study on QCD interactions of heavy mesons with ρ meson

The strong interactions of the negative-parity heavy mesons with ρ   meson may be described consistently in the context of an effective Lagrangian, which is invariant under isospin SU(2)$\mathit{SU}(2)$ transformation. Four coupling constants g_HHρ$g_{HH\rho }$, f_H∗Hρ$f_{H^{\ast }H\rho }$, g_H∗H∗ρ$g_{H^{\ast }{H}^{\ast }\rho }$ and f_H∗H∗ρ$f_{H^{\ast }{H}^{\ast }\rho }$ enter the effective Lagrangian, where H  (H^∗)$(H^{\ast })$ denotes a pseudoscalar bottom or charm meson (the corresponding vector meson). Using QCD light cone sum rule (LCSR) method and, as inputs, the hadronic parameters updated recently, we give an estimate of g_H∗H∗ρ$g_{H^{\ast }{H}^{\ast }\rho }$ and f_H∗H∗ρ$f_{H^{\ast }{H}^{\ast }\rho }$, about which little was known before, and present an improved result for g_HHρ$g_{HH\rho }$ and f_H∗Hρ$f_{H^{\ast }H\rho }$. Also, we examine the heavy quark asymptotic behavior of these nonperturbative quantities and assess the two low energy parameters β and λ of the corresponding effective chiral Lagrangian.     

Hadro-charmonium

We argue that relatively compact charmonium states, J/ψ$J/\psi$, ψ(2S)$\psi (2S)$, χc${\chi }_c$, can very likely be bound inside light hadronic matter, in particular inside higher resonances made from light quarks and/or gluons. The charmonium state in such binding essentially retains its properties, so that the bound system decays into light mesons and the particular charmonium resonance. Thus such bound states of a new type, which we call hadro-charmonium, may explain the properties of some of the recently observed resonant peaks, in particular of Y(4.26)$Y(4.26)$, Y(4.32–4.36)$Y(4.32\text{–}4.36)$, Y(4.66)$Y(4.66)$, and Z(4.43)$Z(4.43)$. We discuss further possible implications of the suggested picture for the observed states and existence of other states of hadro-charmonium and hadro-bottomonium.