arXiv subjects

Amir H. Rezaeian

Publications and source records attributed to Amir H. Rezaeian.

44 records · Page 3Linked to original sources

arXiv2006

The Nuclear matter stability in a non-local chiral quark model

We study the stability of the nuclear matter in a non-local Nambu-Jona-Lasinio model. We work out the equation of state in a relativistic Faddeev approach where we take into account the internal structure of nucleon. We show that the binding energy saturates when the nucleon as a composite particle made of quarks is incorporated. After truncation of the two-body channels to the scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon bound states in medium is solved in the covariant diquark-quark picture. We investigate the nucleon properties in the nuclear medium such as the role of diquarks within the nucleon and the in-medium modification of the nucleon mass and size.

nucl-th↗

arXiv2005

Topics in quantum field theory: Renormalization groups in Hamiltonian framework and baryon structure in a non-local QCD model

In this thesis we investigate aspects of two problems. In the first part of this thesis, we concentrate on renormalization group methods in Hamiltonian framework. We show that the well-known coupled-cluster many-body theory techniques can be incorporated in the Wilsonian renormalization group to provide a very powerful framework for construction of effective Hamiltonian field theories. Eventhough the formulation is intrinsically non-perturbative, we have shown that a loop-expansion can be implemented. As illustrative examples, we apply our formulation on the $Φ^{4}$ theory and an extended Lee model. The many-body problem in an extended Lee model is also studied. We show that a combination of the coupled-cluster theory and the Feshbach projection techniques leads to a renormalized generalized Brueckner theory. The second part of the thesis is rather phenomenologically orientated. In this part, we will employ an effective field-theoretical model as can be constructed by means of the techniques of the first part of the thesis, a quark-confining non-local NJL model and study the baryon and diquarks in this model. After truncation of the two-body channels to the scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon bound states is solved in the covariant diquark-quark picture. We study the possible implications of quark confinement for the description of the diquarks and the nucleon. We also examine alternative field theoretical approaches for describing baryons.

hep-ph↗

arXiv2004

Baryon structure in a quark-confining non-local NJL model

We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model. For certain parameters the model exhibits quark confinement, in the form of a propagator without real poles. After truncation of the two-body channels to the scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon bound states is solved in the covariant diquark-quark picture. The dependence of the nucleon mass on diquark masses is studied in detail. We find parameters that lead to a simultaneous reasonable description of pions and nucleons. Both the diquarks contribute attractively to the nucleon mass. Axial-vector diquark correlations are seen to be important, especially in the confining phase of the model. We study the possible implications of quark confinement for the description of the diquarks and the nucleon. In particular, we find that it leads to a more compact nucleon.

hep-ph↗

arXiv2003

Renormalization of Hamiltonian Field Theory; a non-perturbative and non-unitarity approach

Renormalization of Hamiltonian field theory is usually a rather painful algebraic or numerical exercise. By combining a method based on the coupled cluster method, analysed in detail by Suzuki and Okamoto, with a Wilsonian approach to renormalization, we show that a powerful and elegant method exist to solve such problems. The method is in principle non-perturbative, and is not necessarily unitary.

hep-ph↗

arXiv2003

Coupled-cluster renormalization group

The coupled cluster method (CCM) is one of the most successful and universally applicable techniques in quantum many-body theory. The intrinsic nonlinear and non-perturbative nature of the method is considered to be one of its advantages. We present here a combination of CCM with the Wilsonian renormalization group which leads to a powerful framework for construction of effective Hamiltonian field theories. As a toy example we obtain the two-loop renormalized $ϕ^{4}$ theory.

hep-th↗

arXiv2003

Relativistic Faddeev approach to a non-local NJL model

The diquark and nucleon are studied in a non-local NJL model. We solve the relativistic Faddeev equation and compare the results with the ordinary NJL model. Although the model is quark confining, it is not diquark confining in the rainbow-ladder approximation. We show that the off-shell contribution to the diquark $T$ matrix is crucial for the structure of the nucleon: without its inclusion the attraction in the scalar channel is too weak to form a three-body bound state.

hep-ph↗

arXiv2003

Linked-cluster Tamm-Dancoff Field Theory

To solve the relativistic bound-state problem one needs to systematically and simultaneously decouple the high-energy from the low-energy modes and the many-body from the few-particle states using a consistent renormalization scheme. In a recent paper we have shown that one such approach can be a combination of the coupled cluster method as used in many-body theory and the Wilsonian exact renormalization group. Even though the method is intrinsically non-perturbative, one can easily implement a loop expansion within it. In this letter we provide further support for this aspect of our formalism by obtaining results for the two-loop renormalized $ϕ^{4}$ theory. We show that the non-unitary representation inherent in our method leads to an economic computation and does not produce any non-hermiticity in the relevant terms.

hep-th↗

arXiv2002

Local Casimir Energy for a Wedge with circular outer boundary

The local Casimir energy is investigated for a wedge with and without a circular outer boundary due to the confinement of a massless scalar field with general curvature coupling parameter and satisfying the Dirichlet boundary conditions. Regularization procedure is carried out making use of a variant of the generalized Abel-Plana formula, previously established by one of the authors. The surface divergences in the vacuum expectation values of the energy density near the boundaries are considered. The corresponding results can be applied to the cosmic strings.

hep-th↗