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我们考虑具有“自由”边界条件的Temperley-Lieb(TL)开放量子自旋链,该边界条件与量子变形的sl(2)的自旋表示相关。 我们构造传递矩阵,并使用解析Bethe ansatz确定其特征值和相应的Bethe方程。 我们证明了转移矩阵具有量子群对称性,并且为贝特方程的解数和转移矩阵特征值的简并性提出了明确的公式。 我们提出了壳外Bethe态的代数Bethe ansatz构造,并且我们推测壳上Bethe态是量子组的最高权态。 我们还为壳外Bethe状态与其壳上对偶之间的标量积以及范数的平方提出了一个行列式公式。 我们发现所有这些结果,除了简并值和标量积中的恒定因子外,在某种意义上都是通用的,因为它们不依赖于自旋值。 在附录中,我们简要考虑具有周期性边界条件的封闭TL自旋链,并说明如何改进先前提出的解决方案,以便获得完整的(尽管非通用的)光谱。
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Available online at www.sciencedirect.com
ScienceDirect
Nuclear Physics B 910 (2016) 910–928
www.elsevier.com/locate/nuclphysb
ce:document-thread
Universal Bethe ansatz solution for the Temperley–Lieb
spin chain
Rafael I. Nepomechie
a,∗
, Rodrigo A. Pimenta
a,b
a
Physics Department, P.O. Box 248046, University of Miami, Coral Gables, FL 33124, USA
b
Departamento de Física, Universidade Federal de São Carlos, Caixa Postal 676, CEP 13565-905, São Carlos, Brazil
Received 25
January 2016; received in revised form 27 April 2016; accepted 29 April 2016
Available
online 4 May 2016
Editor: Hubert
Saleur
Abstract
We
consider the Temperley–Lieb (TL) open quantum spin chain with “free” boundary conditions as-
sociated
with the spin-s representation of quantum-deformed sl(2). We construct the transfer matrix, and
determine its eigenvalues and the corresponding Bethe equations using analytical Bethe ansatz. We show
that the transfer matrix has quantum group symmetry, and we propose explicit formulas for the number of
solutions of the Bethe equations and the degeneracies of the transfer-matrix eigenvalues. We propose an
algebraic Bethe ansatz construction of the off-shell Bethe states, and we conjecture that the on-shell Bethe
states are highest-weight states of the quantum group. We also propose a determinant formula for the scalar
product between an off-shell Bethe state and its on-shell dual, as well as for the square of the norm. We find
that all of these results, except for the degeneracies and a constant factor in the scalar product, are universal
in the sense that they do not depend on the value of the spin. In an appendix, we briefly consider the closed
TL spin chain with periodic boundary conditions, and show how a previously-proposed solution can be
improved so as to obtain the complete (albeit non-universal) spectrum.
© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
DOI of linked article: http://dx.doi.org/10.1016/j.nuclphysb.2016.04.044.
*
Corresponding author.
E-mail
addresses: nepomechie@physics.miami.edu (R.I. Nepomechie), pimenta@df.ufscar.br (R.A. Pimenta).
http://dx.doi.org/10.1016/j.nuclphysb.2016.04.045
0550-3213/© 2016
The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
R.I. Nepomechie, R.A. Pimenta / Nuclear Physics B 910 (2016) 910–928 911
1. Introduction
The generators {X
(1)
, ..., X
(N−1)
} of the unital Temperley–Lieb (TL) algebra TL
N
[1],
X
2
(i)
=cX
(i)
,
X
(i)
X
(i±1)
X
(i)
=X
(i)
,
X
(i)
X
(j)
=X
(i)
X
(j)
, |i − j |> 1 , (1.1)
can be used to define the Hamiltonian of an open quantum spin chain of length N with “free”
boundary conditions
H =
N−1
i=1
X
(i)
. (1.2)
This type of model has been the subject of many investigations. For simplicity, we focus here on
the models associated with U
Q
(A
1
) = U
Q
sl(2). The generators X
(i)
have been constructed for
any value of spin s [2,3]. The s = 1/2 case is the well-known quantum-group-invariant spin-1/2
XXZ chain [4]. The s = 1 case is the quantum deformation [2] of the pure biquadratic spin-1
chain [5–7]. These models are integrable; and closed-chain versions with periodic boundary con-
ditions have been in
vestigated for s>1/2using inversion relations [8,9], numerically [10], by
coordinate Bethe ansatz [5,6,11], and by analytical Bethe ansatz [12]. Additional results can be
found in [13–17] for the open chain, and in [18–20] for the closed chain. TL models associated
with higher-rank algebras have also been investigated [21–23].
Despite these and further ef
forts, a number of fundamental problems related to these models,
such as the formulation of an algebraic Bethe ansatz solution, have remained unsolved. Moreover,
the analytical Bethe ansatz solution proposed in [12] does not give the complete spectrum.
The goal of this paper is to address some of these problems. We construct the transfer matrix
corresponding to the Hamiltonian (1.2), and we determine its eigen
values using analytical Bethe
ansatz. We prove that the transfer matrix has quantum group symmetry, which accounts for the
degeneracies of the spectrum. We propose an algebraic Bethe ansatz construction of the Bethe
states, which (when on-shell) we conjecture are highest-weight states of the quantum group. The
scalar product between an of
f-shell Bethe state and an on-shell Bethe state is also considered,
and we conjecture that it can be given in terms of a determinant formula; the square of the norm,
i.e., the scalar product between on-shell Bethe states, follo
ws as a limit.
1
We find that all of these
results, except for the degeneracies and a constant factor in the scalar product, are universal in
the sense that they do not depend on the value of the spin.
Although most of this paper concerns the open TL chain, we briefly consider the closed TL
chain with periodic boundary conditions in an appendix. There we re
visit the analytical Bethe
ansatz computation in [12], and show how the proposed solution can be improved so as to obtain
the complete spectrum. In contrast with the case of the open chain, the solutions of the closed-
chain Bethe equations are not uni
versal, as the Bethe roots depend on the value of the spin.
The outline of this paper is as follo
ws. In section 2 we describe the construction of the Hamil-
tonian (1.2) and the corresponding transfer matrix. In section 3 we use analytical Bethe ansatz
to determine the eigenvalues of the transfer matrix and the corresponding Bethe equations. In
section 4 we show that the transfer matrix has quantum group symmetry
, and we propose explicit
1
Such formulas are generally known as Slavnov [24] and Gaudin–Korepin [25–27] formulas, respectively.
912 R.I. Nepomechie, R.A. Pimenta / Nuclear Physics B 910 (2016) 910–928
formulas for the number of solutions of the Bethe equations and the degeneracies of the transfer-
matrix eigenvalues. In section 5 we present our proposals for the algebraic Bethe ansatz solution
and scalar products. We briefly discuss these results and remaining problems in section 6. We
treat the closed TL chain in Appendix A.
2. Transfer matrix
We begin this section by describing in more detail the construction of the Hamiltonian (1.2).
We then construct the corresponding transfer matrix, which is the generating function of the
Hamiltonian and the higher local conserved commuting quantities, and we review some of its
important properties.
We consider the TL open quantum spin chain corresponding to the spin-s representation of
U
Q
sl(2). The X
(i)
appearing in the Hamiltonian (1.2) are operators on
C
2s+1
⊗N
defined by
X
(i)
=X
i,i+1
, (2.1)
where X is a (2s + 1)
2
by (2s + 1)
2
matrix (an endomorphism of C
2s+1
⊗ C
2s+1
) with the
following matrix elements [2]
m
1
,m
2
|X|m
1
,m
2
=(−1)
m
1
−m
1
Q
m
1
+m
1
δ
m
1
+m
2
,0
δ
m
1
+m
2
,0
, (2.2)
where m
1
, m
2
, m
1
, m
2
=−s, −s +1, ..., s, and s =
1
2
, 1,
3
2
, .... In other words, X
(i)
is an oper-
ator on N copies of C
2s+1
, which acts as X on copies i and i + 1, and otherwise as the identity
operator,
X
(i)
=I
⊗(i−1)
⊗X ⊗I
⊗(N−i−1)
, (2.3)
where I is the identity operator on C
2s+1
. These operators satisfy the TL algebra (1.1), where c
is given by
c =
[
2s + 1
]
Q
=
Q
2s+1
−Q
−2s−1
Q −Q
−1
=
s
k=−s
Q
2k
≡−
q +
1
q
. (2.4)
We assume throughout this paper that Q has a generic value.
The Hamiltonian (1.2) is inte
grable for any value of spin s. In the notation of [12], the corre-
sponding R-matrix is given by [28]
R(u) =
uq −
1
uq
P +
u −
1
u
PX, (2.5)
where P is the permutation matrix on C
2s+1
⊗C
2s+1
. Indeed, the Yang–Baxter equation
R
12
(u
1
/u
2
)R
13
(u
1
/u
3
)R
23
(u
2
/u
3
) = R
23
(u
2
/u
3
)R
13
(u
1
/u
3
)R
12
(u
1
/u
2
) (2.6)
is satisfied. This R-matrix has the unitarity property
R
12
(u)R
21
(u
−1
) = ζ(u)I
⊗2
,ζ(u)=ω(uq
−1
)ω(u
−1
q
−1
), (2.7)
where R
21
=P
12
R
12
P
12
=R
t
1
t
2
12
, and ω(u) is defined as
ω(u) =u −
1
u
. (2.8)
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