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H. Boos

Publications and source records attributed to H. Boos.

At least 19 recordsLinked to original sources
arXiv2022

Flat connection on four-dimensional lattice, related matrix difference equations and their solutions

In the paper [H.Boos, A.Hutsalyuk and Kh.Nirov, J.Phys.A:Math.Theor. 51 (2018) 445202] the reduced density matrix of the sl(3)-invariant fundamental exchange model was calculated for the operator length up to three by means of the reduced quantum Knizhnik-Zamolodchikov equation. In this paper we present the solution of some special difference problem originated from the study of the reduced density matrix for the operator length 4. This difference problem is related to a four-dimensional zero-curvature condition and has a clear geometrical meaning were we have a trivial fiber bundle CP^3 x C^4 with a vector function which takes value in C^4 and the base being the projective space CP^3. The local connection coefficients satisfy the above mentioned zero-curvature or flatness condition. The solution we discuss here is given in terms of the Gamma-function, its logarithmic derivative, hypergeometric functionand some other related functions defined via the functional relations of difference type.

math-ph↗
arXiv2017

Oscillator versus prefundamental representations II. Arbitrary higher ranks

We find the $\ell$-weights and the $\ell$-weight vectors for the highest $\ell$-weight $q$-oscillator representations of the positive Borel subalgebra of the quantum loop algebra $U_q(\mathcal L(\mathfrak{sl}_{l+1}))$ for arbitrary values of $l$. Having this, we establish the explicit relationship between the $q$-oscillator and prefundamental representations. Our consideration allows us to conclude that the prefundamental representations can be obtained by tensoring $q$-oscillator representations.

math-ph↗
arXiv2016

New results on integrable structure of conformal field theory

We explain how to incorporate the action of local integrals of motion into the fermionic basis for the sine-Gordon model and its UV CFT. The examples up to the level 4 are presented. Numerical computation support the results. Possible applications are discussed.

hep-th↗
arXiv2015

Oscillator versus prefundamental representations

For the case of quantum loop algebras $\mathrm U_q(\mathcal L(\mathfrak{sl}_{l + 1}))$ with $l = 1, 2$ we find the $\ell$-weights and the corresponding $\ell$-weight vectors for the representations obtained via Jimbo's homomorphism, known also as evaluation representations. Then we find the $\ell$-weights and the $\ell$-weight vectors for the $q$-oscillator representations of Borel subalgebras of the same quantum loop algebras. This allows, in particular, to relate $q$-oscillator and prefundamental representations.

math-ph↗
arXiv2013

Quantum groups and functional relations for higher rank

A detailed construction of the universal integrability objects related to the integrable systems associated with the quantum group $\mathrm U_q(\mathcal L(\mathfrak{sl}_3))$ is given. The full proof of the functional relations in the form independent of the representation of the quantum group on the quantum space is presented. The case of the general gradation and general twisting is treated. The specialization of the universal functional relations to the case when the quantum space is the state space of a discrete spin chain is described.

math-ph↗
arXiv2012

Universal integrability objects

We discuss the main points of the quantum group approach in the theory of quantum integrable systems and illustrate them for the case of the quantum group $U_q(\mathcal L(\mathfrak{sl}_2))$. We give a complete set of the functional relations correcting inexactitudes of the previous considerations. A special attention is given to the connection of the representations used to construct the universal transfer operators and $Q$-operators.

math-ph↗
arXiv2012

Universal R-matrix and functional relations

We collect and systematize general definitions and facts on the application of quantum groups to the construction of functional relations in the theory of integrable systems. As an example, we reconsider the case of the quantum group $U_q(\mathcal L(\mathfrak{sl}_2))$ related to the six-vertex model. We prove the full set of the functional relations in the form independent of the representation of the quantum group in the quantum space and specialize them to the case of the six-vertex model.

math-ph↗
arXiv2011

On the universal R-matrix for the Izergin-Korepin model

We continue our exercises with the universal $R$-matrix based on the Khoroshkin and Tolstoy formula. Here we present our results for the case of the twisted affine Kac--Moody Lie algebra of type $A^{(2)}_2$. Our interest in this case is inspired by the fact that the Tzitz\'eica equation is associated with $A^{(2)}_2$ in a similar way as the sine-Gordon equation is related to $A^{(1)}_1$. The fundamental spin-chain Hamiltonian is constructed systematically as the logarithmic derivative of the transfer matrix. $L$-operators of two types are obtained by using q-deformed oscillators.

math-ph↗
arXiv2009

Hidden Grassmann Structure in the XXZ Model IV: CFT limit

The Grassmann structure of the critical XXZ spin chain is studied in the limit to conformal field theory. A new description of Virasoro Verma modules is proposed in terms of Zamolodchikov's integrals of motion and two families of fermionic creation operators. The exact relation to the usual Virasoro description is found up to level 6.

hep-th↗
arXiv2008

Hidden Grassmann Structure in the XXZ Model II: Creation Operators

In this article we unveil a new structure in the space of operators of the XXZ chain. We consider the space of all quasi-local operators, which are products of the disorder field with arbitrary local operators. In analogy with CFT the disorder operator itself is considered as primary field. In our previous paper, we have introduced the annhilation operators which mutually anti-commute and kill the primary field. Here we construct the creation counterpart and prove the canonical anti-commutation relations with the annihilation operators. We show that the ground state averages of quasi-local operators created by the creation operators from the primary field are given by determinants.

hep-th↗
arXiv2007

Fermionic basis for space of operators in the XXZ model

In the recent study of correlation functions for the infinite XXZ spin chain, a new pair of anti-commuting operators $b(z), c(z)$ was introduced. They act on the space of quasi-local operators, which are local operators multiplied by the disorder operator. For the inhomogeneous chain with the spectral parameters $ξ_{k}$, these operators have simple poles at $z^2=ξ_{k}^2$. The residues are denoted by $b_{k}, c_{k}$. At $q=i$, we show that the operators $b_{k}, c_{k}$ are cubic monomials in free fermions. In other words, the action of these operators is very simple in the fermion basis. We give an explicit construction of these fermions. Then, we show that the existence of the fermionic basis is a consequence of the Grassmann relation, the equivariance with respect to the action of the symmetric group and the reduction property, which are all valid for the operators $b_{k}, c_{k}$ in the case of generic $q$.

hep-th↗
arXiv2006

Hidden Grassmann structure in the XXZ model

For the critical XXZ model, we consider the space W of operators which are products of local operators with a disorder operator. We introduce two anti-commutative family of operators b(z), c(z) which act on the space W. These operators are constructed as traces over representations of the q-oscillator algebra, in close analogy with Baxter's Q-operators. We show that the vacuum expectation values of operators in W can be expressed in terms of an exponential of a quadratic form of b(z), c(z).

hep-th↗
arXiv2006

Can $B -> X_c \ell ν$ help us extract |V_{ub}| ?

We study radiative corrections to $\bar{B} \to X_c \ell \barν_\ell$ decays assuming the power counting $m_c \sim \sqrt{Λ_QCD m_b}$ for the charm-quark mass. Concentrating on the shape-function region, we use effective field-theory methods to calculate the hadronic tensor at NLO accuracy. From this we deduce a shape-function independent relation between partially integrated $\bar{B} \to X_c\ell\barν_\ell$ and $\bar{B} \to X_u \ell \barν_\ell$ spectra to leading power in $1/m_b$, including first-order corrections in the strong coupling constant. This may provide an independent cross-check on the determination of the CKM element |V_{ub}|.

hep-ph↗
arXiv2006

Shape Functions from B -> X_c \ell ν

We study inclusive semi-leptonic (B -> X_c \ell ν) decay using the power counting m_c ~ \sqrt{Lambda_{QCD} m_b}. Assuming this scaling for the charm-quark mass, the decay kinematics can be chosen to access the shape-function region even in b -> c transitions. To apply effective field theory methods in this region we extend SCET to describe massive collinear quarks. We calculate the tree-level decay rate, including O(Lambda_{QCD}/m_b) power corrections, and show that it factorizes into a convolution of jet and shape functions. We identify a certain kinematical variable whose decay spectrum is proportional to the universal leading-order shape function familiar from b -> u decay, and speculate as to whether information about this shape function can be extracted from data on b -> c decay.

hep-ph↗
arXiv2006

Algebraic representation of correlation functions in integrable spin chains

Taking the XXZ chain as the main example, we give a review of an algebraic representation of correlation functions in integrable spin chains obtained recently. We rewrite the previous formulas in a form which works equally well for the physically interesting homogeneous chains. We discuss also the case of quantum group invariant operators and generalization to the XYZ chain.

hep-th↗
arXiv2006

Density matrix of a finite sub-chain of the Heisenberg anti-ferromagnet

We consider a finite sub-chain on an interval of the infinite XXX model in the ground state. The density matrix for such a subsystem was described in our previous works for the model with inhomogeneous spectral parameters. In the present paper, we give a compact formula for the physically interesting case of the homogeneous model.

hep-th↗
arXiv2005

Traces on the Sklyanin algebra and correlation functions of the eight-vertex model

We propose a conjectural formula for correlation functions of the Z-invariant (inhomogeneous) eight-vertex model. We refer to this conjecture as Ansatz. It states that correlation functions are linear combinations of products of three transcendental functions, with theta functions and derivatives as coefficients. The transcendental functions are essentially logarithmic derivatives of the partition function per site. The coefficients are given in terms of a linear functional on the Sklyanin algebra, which interpolates the usual trace on finite dimensional representations. We establish the existence of the functional and discuss the connection to the geometry of the classical limit. We also conjecture that the Ansatz satisfies the reduced qKZ equation. As a non-trivial example of the Ansatz, we present a new formula for the next-nearest neighbor correlation functions.

hep-th↗