Searcharxiv⌕ Search

arXiv subjects

M. J. Martins

Publications and source records attributed to M. J. Martins.

At least 37 records · Page 2Linked to original sources
arXiv2008

Algebraic Bethe Ansatz for U(1) Invariant Integrable Models: The Method and General Results

In this work we have developed the essential tools for the algebraic Bethe ansatz solution of integrable vertex models invariant by a unique U(1) charge symmetry. The formulation is valid for arbitrary statistical weights and respective number $N$ of edge states. We show that the fundamental commutation rules between the monodromy matrix elements are derived by solving linear systems of equations. This makes possible the construction of the transfer matrix eigenstates by means of a new recurrence relation depending on $N-1$ distinct types of creation fields. The necessary identities to solve the eigenvalue problem are obtained exploring the unitarity property and the Yang-Baxter equation satisfied by the $R$-matrix. The on-shell and off-shell properties of the algebraic Bethe ansatz are explicitly presented in terms of the arbitrary $R$-matrix elements. This includes the transfer matrix eigenvalues, the Bethe ansatz equations and the structure of the vectors not parallel to the eigenstates.

math-ph↗
arXiv2007

The Bethe ansatz approach for factorizable centrally extended S-matrices

We consider the Bethe ansatz solution of integrable models interacting through factorized $S$-matrices based on the central extention of the $\bf{su}(2|2)$ symmetry. The respective $\bf{su}(2|2)$ $R$-matrix is explicitly related to that of the covering Hubbard model through a spectral parameter dependent transformation. This mapping allows us to diagonalize inhomogeneous transfer matrices whose statistical weights are given in terms of $\bf{su}(2|2)$ $S$-matrices by the algebraic Bethe ansatz. As a consequence of that we derive the quantization condition on the circle for the asymptotic momenta of particles scattering by the $\bf{su}(2|2) \otimes \bf{su}(2|2)$ $S$-matrix. The result for the quantization rule may be of relevance in the study of the energy spectrum of the $AdS_5 \times S^{5}$ string sigma model in the thermodynamic limit. \

hep-th↗
arXiv2006

Exact solution and finite size properties of the $U_{q}[osp(2|2m)]$ vertex model

We have diagonalized the transfer matrix of the $U_{q}[osp(2|2m)]$ vertex model by means of the algebraic Bethe ansatz method for a variety of grading possibilities. This allowed us to investigate the thermodynamic limit as well as the finite size properties of the corresponding spin chain in the massless regime. The leading behaviour of the finite size corrections to the spectrum is conjectured for arbitrary $m$. For $m=1$ we find a critical line with central charge $c=-1$ whose exponents vary continuously with the $q$-deformation parameter. For $m\geq 2$ the finite size term related to the conformal anomaly depends on the anisotropy which indicates a multicritical behaviour typical of loop models.

hep-th↗
arXiv2006

Exactly Solvable Models of Interacting Spin-s Particles in one-dimension

We consider the exact solution of a many-body problem of spin-$s$ particles interacting through an arbitrary U(1) invariant factorizable $S$-matrix. The solution is based on a unified formulation of the quantum inverse scattering method for an arbitrary $(2s+1)$-dimensional monodromy matrix. The respective eigenstates are shown to be given in terms of $2s$ creation fields by a general new recurrence relation. This allows us to derive the spectrum and the respective Bethe ansatz equations.

hep-th↗
arXiv2006

Solutions of the reflection equations for the $U_q[G_2]$ vertex model

We investigate the possible regular solutions of the boundary Yang-Baxter equation for the fundamental $U_q[G_2]$ vertex model. We find four distinct classes of reflection matrices such that half of them are diagonal while the other half are non-diagonal. The latter are parameterized by two continuous parameters but only one solution has all entries non-null. The non-diagonal solutions do not reduce to diagonal ones at any special limit of the free-parameters.

nlin.SI↗
arXiv2005

Integrable Vertex Models with General Twists

We review recent progress towards the solution of exactly solved isotropic vertex models with arbitrary toroidal boundary conditions. Quantum space transformations make it possible the diagonalization of the corresponding transfer matrices by means of the quantum inverse scattering method. Explicit expressions for the eigenvalues and Bethe ansatz equations of the twisted isotropic spin chains based on the $B_n$, $D_n$ and $C_n$ Lie algebras are presented. The applicability of this approach to the eight vertex model with non-diagonal twists is also discussed.

nlin.SI↗
arXiv2005

Algebraic Bethe ansatz for an integrable U_q[Sl(n|m)] vertex model with mixed representations

We diagonalize the transfer matrix of a solvable vertex model constructed by combining the vector representation of U_q[Sl(n|m)] and its dual by means of the quantum inverse scattering framework. The algebraic Bethe ansatz solution consider all (n+m)!/(n!m!) possibilities of choosing the grading for arbitrary values of n and m. This allows us to derive the transfer matrix eigenvalues and the respective Bethe ansatz equations for general grading choices.

nlin.SI↗
arXiv2005

New R-matrices from Representations of Braid-Monoid Algebras based on Superalgebras

In this paper we discuss representations of the Birman-Wenzl-Murakami algebra as well as of its dilute extension containing several free parameters. These representations are based on superalgebras and their baxterizations permit us to derive novel trigonometric solutions of the graded Yang-Baxter equation. In this way we obtain the multiparametric $R$-matrices associated to the $U_q[sl(r|2m)^{(2)}]$, $U_q[osp(r|2m)^{(1)}]$ and $U_q[osp(r=2n|2m)^{(2)}]$ quantum symmetries. Two other families of multiparametric $R$-matrices not predicted before within the context of quantum superalgebras are also presented. The latter systems are indeed non-trivial generalizations of the $U_q[D^{(2)}_{n+1}]$ vertex model when both distinct edge variables statistics and extra free-parameters are admissible.

nlin.SI↗
arXiv2004

Bethe ansatz for the XXX-S chain with non-diagonal open boundaries

We consider the algebraic Bethe ansatz solution of the integrable and isotropic XXX-S Heisenberg chain with non-diagonal open boundaries. We show that the corresponding K-matrices are similar to diagonal matrices with the help of suitable transformations independent of the spectral parameter. When the boundary parameters satisfy certain constraints we are able to formulate the diagonalization of the associated double-row transfer matrix by means of the quantum inverse scattering method. This allows us to derive explicit expressions for the eigenvalues and the corresponding Bethe ansatz equations. We also present evidences that the eigenvectors can be build up in terms of multiparticle states for arbitrary S.

nlin.SI↗
arXiv2004

Mixed integrable SU(N) vertex model with arbitrary twists

We consider the quantum inverse scattering method for several mixed integrable models based on the rational SU(N) R-matrix with general toroidal boundary conditions. This includes systems whose Hilbert spaces are invariant by the discrete representations of the group SU(2) and the non-compact group SU(1,1) as well as the conjugate representation of the SU(N) symmetry. Introducing certain transformations on the quantum spaces we are able to solve generalizaed impurity problems including those related to singular matrices.

nlin.SI↗
arXiv2004

R-matrices and Spectrum of Vertex Models based on Superalgebras

In this paper we investigate trigonometric vertex models associated with solutions of the Yang-Baxter equation which are invariant relative to q-deformed superalgebras sl(r|2m)^(2), osp(r|2m)^(1) and osp(r=2n|2m)^(2). The associated R-matrices are presented in terms of the standard Weyl basis making possible the formulation of the quantum inverse scattering method for these lattice models. This allowed us to derive the eigenvectors and the eigenvalues of the corresponding transfer matrices as well as explicit expressions for the Bethe ansatz equations.

nlin.SI↗
arXiv2003

Integrable SU(N) vertex models with general toroidal boundary conditions

We formulate the algebraic Bethe ansatz solution of the SU(N) vertex models with rather general non-diagonal toroidal boundary conditions. The reference states needed in the Bethe ansatz construction are found by performing gauge transformations on the Boltzmann weights in the manner of Baxter [1]. The structure of the transfer matrix eigenvectors consists of multi-particle states over such pseudovacuums and the corresponding eigenvalues depend crucially on the boundary matrix eigenvalues. We also discuss for N=2 the peculiar case of twisted boundaries associated to singular matrices.

nlin.SI↗
arXiv2003

Algebraic Bethe ansatz for a class of coupled asymmetric six-vertex free-fermion model

We present an algebraic Bethe ansatz for certain submanifolds of the bilayer vertex models proposed by Shiroishi and Wadati as coupled asymmetric six-vertex free-fermion models. A peculiar feature of our formulation is the presence of a diagonal monodromy matrix element that does not generate unwanted terms. The model contains two free-parameters entering into the Bethe ansatz equations as a pure phase factor.

nlin.SI↗
arXiv2003

Yang-Baxter equation for the asymmetric eight-vertex model

In this note we study `a la Baxter [1] the possible integrable manifolds of the asymmetric eight-vertex model. As expected they occur when the Boltzmann weights are either symmetric or satisfy the free-fermion condition but our analysis clarify the reason both manifolds need to share a universal invariant. We also show that the free-fermion condition implies three distinct classes of integrable models.

nlin.SI↗
arXiv2000

The excitations of the sympletic integrable models and their applications

The Bethe ansatz equations of the fundamental Sp(2N) integrable model are solved by a peculiar configuration of roots leading us to determine the nature of the excitations. They consist of N elementary generalized spinons and N-1 composite excitations made by special convolutions between the spinons. This fact is essential to determine the low-energy behaviour which is argued to be described in terms of 2N Majorana fermions. Our results have practical applications to spin-orbital systems and also shed new light to the connection between integrable models and Wess-Zumino-Witten field theories.

cond-mat.stat-mech↗
arXiv2000

Exact and numerical results for the dimerized spin-orbital model

We establish exact results for the one-dimensional spin-orbital model for special values of the four-spin interaction $V$ and dimerization parameter $δ$. The first exact result is at $δ=1/2$ and $V=-2$. Because we find a very small but finite gap in this dimerized chain, this can serve as a very strong test case for numerical and approximate analytical techniques. The second result is for the homogeneous chain with $V=-4$ and gives evidence that the system has a spontaneously dimerized ground state. Numerical results indicate that the interplay between dimerization and interaction could result in gapless phases in the regime $0\leq V<-2$.

cond-mat.stat-mech↗
arXiv2000

Integrability of the $D_n^2$ vertex models with open boundary

We investigate various aspects of the integrability of the vertex models associated to the $D_n^2$ affine Lie algebra with open boundaries. We first study the solutions of the corresponding reflection equation compatible with the minimal symmetry of this system. We find three classes of general solutions, one diagonal solution and two non-diagonal families with a free parameter. Next we perform the Bethe ansatz analysis for some of the associated open $D_2^2$ spin chains and we identify the boundary having quantum group invariance. We also discuss a new $D_2^2$ $R$-matrix.

nlin.SI↗