arXiv subjects

A. Delfino

Publications and source records attributed to A. Delfino.

50 records · Page 3Linked to original sources

arXiv2001

Fixed-Point Hamiltonians in Quantum Mechanics

We show how to derive fixed-point Hamiltonians in quantum mechanics from a proposed renormalization group invariance approach that relies in a subtraction procedure at a given energy scale. The scheme is valid for arbitrary interactions that originally contain point-like singularities (as the Dirac-delta and/or its derivatives). One example of diagonalization of a fixed-point Hamiltonian illustrates the procedure for an interaction that contains regular and singular parts. In another example, the fixed point Hamiltonian is derived for the case of higher order singularities in the interaction.

hep-ph↗

arXiv2000

Pin-Hole Water Flow from Cylindrical Bottles

We performed an experiment on elementary hydrodynamics. The basic system is a cylindrical bottle from which water flows through a pin-hole located at the bottom of its lateral surface. We measured the speed of the water leaving the pin-hole, as a function of both the time and the current level of water still inside the bottle. The experimental results are compared with the theory. The theoretical treatment is a very simple one based on mass and energy conservation, corresponding to a widespread exercise usually adopted in university basic disciplines of Physics. We extended the previous experiment to another similar system using two equal bottles with equal pin-holes. The water flowing from the first bottle feeds the second one located below it. The same concepts of mass and energy conservation now lead to a non-trivial differential equation for the lowest bottle dynamics. We solved this equation both numerically and analytically, comparing the results with the experimental data.

cond-mat↗

arXiv1999

Virtual states of light non-Borromean halo nuclei

It is shown that the three-body non-Borromean halo nuclei like ^{12}Be, ^{18}C, ^{20}C have p-wave virtual states with energy of about 1.6 times the corresponding neutron-core binding energy. We use a renormalizable model that guarantees the general validity of our results in the context of short range interactions.

nucl-th↗

arXiv1998

Modified Zimanyi-Moszkowski Model for Finite Nuclei

By scaling the mesonic masses in the Walecka model, to the inverse of the hadronic effective mass in medium, we generate the Zimanyi-Moszkowski (ZM) models added to a surface term. For infinite nuclear matter, the surface term vanishes and this new model becomes equivalent to the usual ZM model. For finite nuclei calculations, the surface contribution changes the spin-orbit splitting in the right experimental direction. Calculations for some nuclei are presented.

nucl-th↗

arXiv1998

Alternative Linear Chiral Models for Nuclear Matter

The equation of state of a family of alternative linear chiral models in the mean field approximation is discussed. We investigate the analogy between some of these models with current models in the literature, and we show that it is possible to reproduce very well the saturation properties of nuclear matter.

nucl-th↗

arXiv1997

The Two - Dimensional Attractive Hubbard Model: Highly Non-Linear Superconductivity With Sum Rules

We use the moment approach of Nolting (exact sum rules) (Z. Physik 255, 25 (1972)) for the attractive Hubbard model in the superconducting phase. Our diagonal and off - diagonal spectral functions are constructed and evaluated with the sum rules. They reduce to the $BCS$ limit for weak interaction. However, the presence of correlations modify the $BCS$ picture dramatically. For example, due to the presence of correlations we have postulated a three - pole ansatz for the diagonal Green function, $G(\vec{k},ω)$, while the off - diagonal one, $B(\vec{k},ω)$, is supposed to have two poles. In the paper we present results for the three spectral weights of the diagonal Green function, $α_j(\vec{k})$, j = 1,2,3. Our results compare reasonably well with more elaborated auto - consistent highly non - linear equations (double fluctuation calculations in the $T-$ Matrix approach of one of the authors). Then, the physical picture which emerges is that the lower Hubbard band is split due to the superconducting gap and the upper Hubbard band remains mostly unmodified.

cond-mat↗

arXiv1996

Finite Nuclei in a Relativistic Mean-Field Model with Derivative Couplings

We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski model and one of its variations (the ZM3 model). We calculate energy levels and ground-state properties in nuclei where the mean-field approach is reliable. The role played by the spin-orbit potential in sorting out mean-field model descriptions is emphasized.

nucl-th↗

arXiv1996

Moment Approach for the 2D Attractive Hubbard Model

We constructed the one-particle spectral functions (diagonal and off-diagonal) which reproduce BCS for weak coupling and which take into account the effect of correlations on superconductivity in the attractive Hubbard model. The diagonal spectral function is composed of three peaks and the off-diagonal one is composed of two peaks. This ansatz satisfies the sum rules for the first six moments. Our solutions are valid for intermediate coupling, i.e., for $U/t \approx -4.0$. Our set of analytical equations for the unknown variables is self-consistent and has been solved numerically in lowest order of the order parameter. As a result, we obtain that the presence of the third band, or {\it upper Hubbard band}, strongly renormalizes the two lower bands, making that the energy gap be ${\bf k}$-dependent while the order parameter is pure s-wave. This shows that the order parameter and the gap are two different quantities.

cond-mat↗

arXiv1996

Phase Transition in Warm Nuclear Matter with Alternative Derivative Coupling Models

An analysis is performed of the liquid-gas phase transition of nuclear matter obtained from different versions of scalar derivate coupling suggested by Zimanyi and Moszkowski (ZM) and the results are compared with those obtained from the Walecka model. We present the phase diagram for the models and one of them, the ZM3 model, has the lowest critical temperature $T_c=13.6$ MeV with the lowest critical density $ρ_c=0.037$ f$m^{-3}$ and pressure $p_c=0.157$ MeV f$m^{-3}$. These results are in accord with recent observations from energetic heavy-ion collisions, which suggest a small liquid-gas phase region.

nucl-th↗

arXiv1996

QCD phase transitions from relativistic hadron models

The models of translationally invariant infinite nuclear matter in the relativistic mean field models are very interesting and simple, since the nucleon can connect only to a constant vector and scalar meson field. Can one connect these to the complicated phase transitions of QCD ? For an affirmative answer to this question, one must consider models where the coupling constants to the scalar and vector fields must depend on density in a non-linear way, since as such the models are not explicitly chirally invariant. Once this is ensured, indeed one can derive a quark condensate indirectly from the energy density of nuclear matter which goes to zero at large density and temperature. The change to zero condensate indicates a smooth phase transition.

hep-ph↗

arXiv1996

Nuclear Matter Properties in Derivative Coupling Models Beyond Mean - Field Approximation

The structure of infinite nuclear matter is studied with two of the Zimanyi - Moszkowski (ZM) models in the framework of a relativistic approximation which takes into account Hartree terms and beyond and is compared with the results which come out of the relativistic Hartree - Fock approach in the linear Walecka model. The simple treatment applied to these models can be used in substitution to the more complicated Dirac - Brueckner - Hartree - Fock method to perform future calculations in finite nuclei.

nucl-th↗

arXiv1996

How reliable is the mean-field Nuclear Matter description for supporting Chiral Effective Lagrangians?

The link between non-linear chiral effective Lagrangians and the Walecka model description of bulk nuclear matter [1] is questioned. This fact is by itself due to the Mean Field Approximation (MFA) which in nuclear mater makes the picture of a nucleon-nucleon interaction based on scalar(vector) meson exchange, equivalent to the description of a nuclear matter based on attractive and repulsive contact interactions. We present a linear chiral model where this link between the Walecka model and an underlying to chiral symmetry realization still holds, due to MFA.

nucl-th↗

arXiv1996

The connection between the nuclear matter mean-field equation of state and the quark and gluon condensates at high density

It is known now that chiral symmetry restoration requires the meson-nucleon coupling to be density dependent in nuclear-matter mean-field models. We further show that quite generally, the quark and gluon condensates in medium are related to the trace of energy-momentum tensor of nuclear matter and in these models the incompressibility, K, must be less than thrice the chemical potential, $μ$. In the critical density $ρ_c$, the gluon condensate is only reduced by $20\%$ indicating a larger effective nucleon mass.

hep-ph↗

arXiv1996

Derivative-Coupling Models and the Nuclear-Matter Equation of State

The equation of state of saturated nuclear matter is derived using two different derivative-coupling Lagrangians. We show that both descriptions are equivalent and can be obtained from the sigma-omega model through an appropriate rescaling of the coupling constants. We introduce generalized forms of this rescaling to study the correlations amongst observables in infinite nuclear matter, in particular, the compressibility and the effective nucleon mass.

nucl-th↗