The semiclassical description of Skyrmions at small isospin chemical potential $μ_I$ is carefully analyzed. We show that when the calculation of the energy of a nucleon is performed using the straightforward generalization of the vacuum sector techniques ($μ_I=0$), together with the "natural" assumption $μ_I = {\cal O} (N_c^0)$, the proton and neutron masses are nonlinear in $μ_I$ in the regime $|μ_I| < m_π$. Although these nonlinearities turn out to be numerically quite small, such a result fails to strictly agree with the very robust prediction that for those values of $\mui$ the energy excitations above the vacuum are linear in $μ_I$. The resolution of this paradox is achieved by studying the realization of the large $N_c$ limit of $QCD$ in the Skyrme model at finite $\mui$. This is done in a simplified context devoid of the technical complications present in the Skyrme model but which fully displays the general scaling behavior with $N_c$. The analysis shows that the paradoxical result appears as a symptom of using the semi-classical approach beyond its regime of validity and that, at a formal level, the standard methods for dealing with the Skyrme model are only strictly justified for states of high isospin $I \sim N_c$.
The stability of the Skyrmion solution in the presence of finite isospin chemical potential $μ$ is considered, showing the existence of a critical value $μ_{c} = 222.8$ MeV where the Skyrmion mass vanishes. Using the Hamiltonian formulation, in terms of collective variables, we discuss the behavior of different skyrmionic parameters as function of the isospin chemical potential ($μ$), such as the energy density, the isoscalar radius and the isoscalar magnetic radius. We found that the radii start to grow very fast for $μ\geq 140$ MeV, suggesting the occurrence of a phase transition.
We analyze the existence of localized finite energy topological excitations on top of the perturbative pion vacuum within the Skyrme model at finite isospin chemical potential and finite pion mass. We show that there is a critical isospin chemical potential $μ_I^c$ above which such solutions cease to exist. We find that $μ_I^c$ is closely related to the value of the pion mass. In particular for vanishing pion mass we obtain $μ_I^c=0$ in contradiction with some results recently reported in the literature. We also find that below $\mui^c$ the skyrmion mass and baryon radius show, at least for th…
Using the Hamiltonian formulation, in terms of collective variables, we explore the evolution of different skyrmionic parameters as function of the isospin chemical potential ($μ$), such as the energy density, the charge density, the isoscalar radius and the isoscalar magnetic radius. We found that the radii start to grow very fast for $μ\gtrsim 140$ MeV, suggesting the occurrence of a phase transition.
We discuss the stability of the Skyrmion solution in the presence of a finite isospin chemical potential $μ$. Solving numerically the mass of the Skyrmion as function of $μ$, we find a critical value $μ_c=222.8$ MeV where the Skyrmion mass vanishes. We compare the exact numerical treatment with an analytical discussion based on a special shape for the profile of the Skyrmion due to Atiyah and Manton. The extension of this ansatz for finite $μ$ works quite well for $μ<121$ MeV. Then, for small values of $μ$, where the analytical approach is valid, we consider the possibility of having an angula…
The density of states and energy spectrum of the gluon radiation are calculated for the color current of an expanding hydrodynamic skyrmion in the quark gluon plasma with a semiclassical method. Results are compared with those in literatures.
A quantisation of chiral symmetry within the Skyrme crystal is carried out. The definition of global isospin in the crystal is explored, and found to be ambiguous. However, the state corresponding to a neutron crystal is identified, and the leading quantum correction to the classical mass is computed. The results are compared to those of Klebanov for a crystal of whole skyrmions.
In the Skyrme model, the Lagrangian can be quantized in several ways using the collective coordinate approach. Not all of which produce quantum states that can be interpreted as physical particles. For example the SU(2) collective coordinate approach produces both integral and half-integral spin and isospin states. Only half of these are the physical baryons. Less well known is the fact that it is equally possible to quantize the system using the SO(3) collective coordinates. This produces only unphysical integral spin and isospin states. To fulfill the goal of being able to express a classica…
Dynamics of two-Skyrmion systems is studied in the quasistatic approach. The quasistatic approach enables us to formulate the collective coordinate quantization of two-Skyrmion systems consistently with the 1/Nc expansion. By constructing quasistatic field configurations for largely separated two Skyrmions, their energies are computed for three independent relative orientations of the Skyrmions in the isospin space. The obtained energies are much lower than those for the product approximation. In particular, the repulsion in the two-pion range is considerably reduced.
We present the complete solution to the so-called ``Yukawa problem'' of the Skyrme model. This refers to the perceived difficulty of reproducing---purely from soliton physics---the usual pseudovector pion-nucleon coupling, echoed by pion coupling to the higher spin/isospin baryons $(I=J=3/2 , 5/2 , \cdots , N_c/2 )$ in a manner fixed by large-$N_c$ group theory. The solution involves surprisingly elegant interplay between the classical and quantum properties of a new configuration, the ``new improved skyrmion''. This is the near-hedgehog obtained by minimizing the usual skyrmion mass functiona…
We analyze the stability of different topological solutions in Quantum Field Theory when an isospin chemical potential $μ$ is included. We work in the limit when temperature vanishes. We find that static vortex solutions in $2+1D$ do exist. However, the 't Hooft-Polyakov monopole in $3+1D$ is no longer stable, as soon as the chemical potential acquires a finite value. In the case of the Skyrmion, this topological solution still exists for finite $μ$, up to a certain critical value.
The relatively small binding energy in nuclei suggests that they may be well represented by near-BPS Skyrmions since their mass is roughly proportional to the baryon number $A.$ For that purpose, we propose a generalization of the Skyrme model with terms up to order six in derivatives of the pion fields and treat the nonlinear $σ$ and Skyrme terms as small perturbations. For our special choice of mass term (or potential) $V$, we obtain well-behaved analytical BPS-type solutions with non-shell configurations for the baryon density, as opposed to the more complex shell-like configurations found …
A discussion of the stability of self gravitating Skyrmions, with a large winding number N, in a Schwarzschild type of metric, is presented for the case where an isospin chemical potential is introduced. It turns out that the chemical potential stabilizes the behavior of the Skyrmion discussed previously in the literature. This analysis is carried on in the framework of a variational approach using different ansaetze for the radial profile of the Skyrmion. We found a divergent behavior for the size of the Skyrmion, associated to a certain critical value $μ_c$ of the chemical potential. At this…
The Skyrme model is extended with a sextic derivative term - called the BPS-Skyrme term - and a repulsive potential term - called the loosely bound potential. A large part of the model's parameter space is studied for the 4-Skyrmion which corresponds to the Helium-4 nucleus and emphasis is put on preserving as much of the platonic symmetries as possible whilst reducing the binding energies. We reach classical binding energies for Helium-4 as low as 0.2%, while retaining the cubic symmetry of the 4-Skyrmion, and after taking into account the quantum mass correction to the nucleon due to spin/is…
We study the posibility of large isospin fluctuations in high-energy heavy-ion collisions by assuming that pions are produced semiclassically both directly and in pairs through the isovector channel. The leading-particle effect and the factorization property of the scattering amplitude in the impact parameter space are used to define the classical pion field. In terms of the joint probability function $P_{II_{3}}(n_{0},n_{\_})$ for producing $n_{0}$ neutral and $n_{\_}$ negative pions from a definite isospin state $II_{3}$ of the incoming leading-particle system we calculate the two pion corre…
We present the study of the influence of the leading contribution from the kinetic energy of the Skyrme Lagrangian on the scattering of low energy nucleons. This classical kinetic energy for the 2-body system is computed using the product ansatz and is correct for low energy, well separated Skyrmions. We quantize the rotational degrees of freedom of the Skyrmions in order to give them the right spin and isospin values. We are then able to compute analytically the scattering angles for some angular momenta polarizations.
We study the (anti)kaon nucleon interaction in the Skyrme model. The kaon field is introduced as a fluctuation around the rotating Skyrmion for the nucleon. As an extension of our previous work, we study scattering states and examine phase shifts in various kaon-nucleon channels. Then we study the interaction, where we find that it consists of central and spin-orbit components for isospin channels, $I = 0, 1$, with energy dependence and nonlocality. The interaction is then fitted to a Shrödinger equivalent local potential for s- and p-waves.
We study a generalization of the loosely bound Skyrme model which consists of the Skyrme model with a sixth-order derivative term - motivated by its fluid-like properties - and the second-order loosely bound potential - motivated by lowering the classical binding energies of higher-charged Skyrmions. We use the rational map approximation for the Skyrmion of topological charge B=4, calculate the binding energy of the latter and estimate the systematic error in using this approximation. In the parameter space that we can explore within the rational map approximation, we find classical binding en…
In the Skyrme model of nucleons and nuclei, the spin excitation energy of the nucleon is traditionally calculated by a fit of the rigid rotor quantization of spin/isospin of the fundamental Skyrmion (the hedgehog) to the masses of the nucleon and the Delta resonance. The resulting, quite large spin excitation energy of the nucleon of about $ 73\, \mbox{MeV}$ is, however, rather difficult to reconcile with the small binding energies of physical nuclei, among other problems. Here we argue that a more reliable value for the spin excitation energy of the nucleon, compatible with many physical cons…
A quantization of a breathing motion of a rotating chiral soliton on $S^3$ is performed in terms of a family of trial functions for a profile function of the hegdehog ansatz. We determine eigenenergies of the quantized $S^3$ skyrmion by solving the Schrödinger equation of the breathing mode for several lower spin and isospin states varying the Skyrme term constants $e$. When $S^3$ radius is smaller than $2/ef_π$, where $f_π$ is the pion decay constant, we always obtain a conformal map solution as the lowest eigenenergy state. In the conformal map case, allowed states have only symmetric or ant…
