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Common framework and quadratic Bethe equations for rational Gaudin magnets in arbitrarily oriented magnetic fields
by Alexandre Faribault, Hugo Tschirhart
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Submission summary
Authors (as registered SciPost users):  Alexandre Faribault · Hugo Tschirhart 
Submission information  

Preprint Link:  http://arxiv.org/abs/1704.01873v2 (pdf) 
Date accepted:  20170721 
Date submitted:  20170703 02:00 
Submitted by:  Faribault, Alexandre 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
In this work we demonstrate a simple way to implement the quantum inverse scattering method to find eigenstates of spin1/2 XXX Gaudin magnets in an arbitrarily oriented magnetic field. The procedure differs vastly from the most natural approach which would be to simply orient the spin quantisation axis in the same direction as the magnetic field through an appropriate rotation. Instead, we define a modified realisation of the rational Gaudin algebra and use the quantum inverse scattering method which allows us, within a slightly modified implementation, to build an algebraic Bethe ansatz using the same unrotated reference state (pseudovacuum) for any external field. This common framework allows us to easily write determinant expressions for certain scalar products which would be highly nontrivial in the rotated system approach.
Published as SciPost Phys. 3, 009 (2017)
List of changes
The issue of completeness has been addressed in section 6. Indeed, in https://scipost.org/submissions/1603.03542v4/ the completeness of the Quadratic Bethe equations in the usual (zoriented field) XXX case has been demonstrate. The simple oneone correspondence between eigenstates in the generic field and the zoriented case which was presented in this section (simple shift of the eigenvalues) consequently leads to a “trivial” homotopy which preserves the completeness in the case treated here.
Following a referee’s suggestion, we have vastly expanded the discussion concerning other approaches (and consequently the list of references as well) which have been developed to deal with similar situations in a variety of integrable models. Instead of simply mentioning separation of variables, we present a broader picture of the many techniques, which should give the interested reader much more material to look into. From the sheer number of such approaches, it is in our opinion well beyond the scope of this work, to present explicitly the numerous formal possible links to our work.
We have also added references to Claeys’ work on the p+ip superconductor, which has also made use of the same technique in this explicit XXZGaudin case as well as that of Lukayenko on the same subject which, despite not discussing explicitly the eigenstates of the system has also derived similar conserved charges, Bethe equations and eigenvalues.
Section 5 has been slightly modified to make the final result appear at the very end of the section while section 4 has been reworked in order to regroup the results at beginning and leave the rest of the section as proof.
We also added a short discussion of the “triangular boundary” case, where the proposed ansatz using as many Bethe roots as we have spins, would no longer be valid. In this case, eigenstates are defined by a smaller number of Bethe roots as the pseudovacuum is now a properly defined eigenstate of the transfer matrix.
As it was explicitly mentioned in one of the reports, we added subsection 7.1 to give explicit determinant formulas the scalar products between generic offtheshell Bethe states and generic offtheshell dual states, for a given fixed (but generic) orientation of the field. This has lead to a slight shortening of 7.2, since the formulas for the canonical basis projections are obtained in an more or less identical fashion as those in 7.1
The various typos, notational errors and small precisions requested in the various reports have also all been explicitly addressed.
Submission & Refereeing History
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Reports on this Submission
Anonymous Report 3 on 2017718 (Invited Report)
 Cite as: Anonymous, Report on arXiv:1704.01873v2, delivered 20170718, doi: 10.21468/SciPost.Report.193
Strengths
Same as before
Weaknesses
Same as before
Report
I believe the minor issues raised by the referees have been all successfully addressed.
Requested changes
None
Anonymous Report 1 on 201777 (Invited Report)
 Cite as: Anonymous, Report on arXiv:1704.01873v2, delivered 20170707, doi: 10.21468/SciPost.Report.184
Strengths
The authors solve analytically an integrable model using the algebraic Bethe ansatz but without pseudovacuum.
Weaknesses
n/a
Report
The authors modified the paper as requested
Requested changes
No change