Emmanuel Briand's Publications 
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Articles in Journals




The stability of the Kronecker products of Schur functions.
Emmanuel Briand, Rosa Orellana and Mercedes Rosas.
Journal of Algebra,
vol. 331(1) pp. 1127 (2011).
In the late 1930's Murnaghan discovered the existence of a stabilization phenomenon for the Kronecker product of Schur functions. For n sufficiently large, the values of the Kronecker coefficients appearing in the product of two Schur functions of degree n do not depend on the first part of the indexing partitions, but only on the values of their remaining parts. We compute the exact value of n for which all the coefficients of a Kronecker product of Schur functions stabilize. We also compute two new bounds for the stabilization of a sequence of coefficients and show that they improve existing bounds of M. Brion and E. Vallejo.




Reduced Kronecker coefficients and counterexamples to Mulmuley's strong saturation conjecture SH.
Emmanuel Briand, Rosa Orellana and Mercedes Rosas.
Computational Complexity,
vol. 18(4) pp. 577600 (2009).
We provide counterexamples to Mulmuley's strong saturation conjecture (strong SH) for the Kronecker coefficients. This conjecture was proposed in the setting of Geometric Complexity Theory to show that deciding whether or not a Kronecker coefficient is zero can be done in polynmial time. We also provide a short proof of the #Phardness of computing the Kronecker coefficients and another family of structural constants in the representation theory of the symmetric groups, Murnaghan's reduced Kronecker coefficients. An appendix by Mulmuley introduces a relaxed form of the saturation hypothesis SH, still strong enough for the aims of Geometric Complexity Theory.



 
Milne's volume function and vector symmetric polynomials.
Emmanuel Briand and Mercedes Rosas.
Journal of Symbolic Computation
vol. 44, pp. 583590 (2009).
The volume function introduced by P. Milne to count the real roots of a system of polynomial equations in a box is a vector symmetric polynomial. Its expansion in the basis of monomial functions is provided. Only monomial functions of a particular kind appear in this expansion ("squarefree monomial functions"). By means of an appropriate specialization of the vector symmetric Newton identities, we derive an inductive formula to decompose the squarefree monomial functions in power sums. This formula is related to the lattice of the subhypergraphs of an hypergraph. As a corollary, an inductive formula to express the components of Milne's volume function in the power sums is obtained.


 
On the S_nmodule structure of the noncommutative harmonics.
Emmanuel Briand, Mercedes Rosas and Mike Zabrocki.
Journal of Combinatorial Theory, series A
vol. 115(6), pp. 10771085 (2008).
Using the a noncommutative version of Chevalley's theorem due to Bergeron, Reutenauer, Rosas, and Zabrocki we compute the graded Frobenius series for their two sets of noncommutative harmonics with respect to the left action of the symmetric group (acting on variables). We use these results to derive the Frobenius series for the enveloping algebra of the derived free Lie algebra in n variables.
The paper on arxiv ( on the left) is an expanded version of the published paper.




Equations, inequations and inequalities characterizing the configurations of two real projective conics.
Emmanuel Briand.
Applicable Algebra in Engineering, Communication and Computing
vol. 18 (12), pp. 2152 (2007).
Ordered pairs of
proper, nonempty real
projective conics can be classified modulo rigid isotopy and ambient isotopy.
We characterize the classes
by equations, inequations and
inequalities in the coefficients of the quadratic forms defining the
conics.
The results are welladapted to the study of the relative position of two
conics defined by equations depending on parameters.


 
On a matrix function interpolating between determinant and permanent.
Emmanuel Briand.
Linear Algebra and its applications
vol. 411 (special issue on Determinants and the legacy of Sir Thomas Muir), pp. 343347 (2005).
A matrix function, depending on a parameter t, and interpolating between the determinant and the permanent, is introduced.
It is shown this function admits a simple expansion in terms of determinants and permanents of submatrices.
This expansion is used to explain some formulas ocurring in the resolution of some systems of algebraic equations.


 
The moduli space of three qutrit states.
Emmanuel Briand, JeanGabriel Luque, JeanYves Thibon and Frank Verstraete.
Journal of Mathematical Physics
vol. 45, num. 12, pp. 48554867, (2004).
We investigate the normal forms of pure entangled threepartite qutrit states under local filtering operations. This amounts to study the orbits of the group $SL(3,C)^{\times 3}$ acting on $(C^3)^{\otimes 3}$. We describe the moduli space of this action in terms of a very symmetric normal form parameterized by three complex numbers. The parameters of the possible normal forms of a given state are roots of an algebraic equation, which is proved to be solvable by radicals in a completely explicit way. The structure of the sets of equivalent normal forms is related to the geometry of certain regular complex polytopes.


 
When is the Algebra of Multisymmetric Polynomials generated by the Elementary Multisymmetric Polynomials ?.
Emmanuel Briand.
Beiträge zur Algebra und Geometrie
vol.45(2), 353368 (2004).
Multisymmetric polynomials are the diagonal invariants
of the symmetric group. Elementary multisymmetric polynomials are analogues
of the elementary symmetric polynomials, in the multisymmetric setting.
In this paper, we give a necessary and sufficient condition on a ring A
for an algebra of multisymmetric polynomials with coefficients in A to
be generated by the elementary multisymmetric polynomials.


 
A Complete Set of Covariants of the Four Qubit System.
Emmanuel Briand, JeanGabriel Luque and JeanYves Thibon.
Journal of Physics A: Math. Gen.
38, pp. 99159927 (2003).
We obtain a complete and minimal set of 170 generators
for the algebra of $SL(2,C)^{\times 4}$covariants of a four qubit system.
This sheds light on the structure of the SLOCC orbits in the Hilbert space
of this system, as well as on the more complicated algebra of its local
unitary invariants.


 
Multivariate Newton Sums : Identities and Generating Functions.
Emmanuel Briand and Laureano GonzálezVega.
Communications in Algebra
vol. 30, num. 9, pp. 45274547 (2002).
This article is devoted to present, first, a family of formulas extending
to the multivariate case the classical Newton Identities relating the coefficients
of an univariate polynomial equation with its roots through the Power Sums
and, secondly, the Generating Functions associated to the introduced Power
Sums of the multivariate case. As a byproduct the kinds of systems accepting
these Newton Identities are also characterized together with those allowing
the Power Sums to be computed in an inductive way directly from the coefficients
of the polynomial system under consideration.


Book chapters


 
Covariants decomposing on totally decomposable forms.
Emmanuel Briand.
pp. 237256 in
Liaison, Schottky Problem and Invariant Theory. Remembering Federico Gaeta
,
ed: Alonso M.E., Arrondo E., Mallavibarrena R., Sols I. Progress in Mathematics 280, Birkhauser (2010).
We consider the problem of providing systems of equations characterizing the forms with complex coefficients that are totally decomposable, i.e. products of linear forms. Our focus is computational. We present the wellknown solution given at the end of the nineteenth century by Brill and Gordan and give a complete proof that their system does vanish only on the decomposable forms. We explore an idea due to Federico Gaeta which leads to an alternative system of equations, vanishing on the totally decomposable forms and on the forms admitting a multiple factor. Last, we give some insight on how to compute efficiently these systems of equations and point out possible further improvements.





Some covariants related to Steiner surfaces.
Franck Aries, Emmanuel Briand and Claude Bruchou.
pp. 3146 in
Geometric Modeling and Algebraic Geometry,
ed. Bert Jüttler and Ragni Piene, Springer, ISBN 9783540721840 (2008).
A Steiner surface is the generic case of a quadratically
parameterizable quartic surface used in geometric modeling.
This paper studies quadratic parameterizations of surfaces under the
angle of Classical Invariant Theory. Precisely, it exhibits a
collection of covariants associated to projective quadratic
parameterizations of surfaces, under the actions of linear
reparameterization and linear transformations of the goal space. Each
of these covariants comes with a simple geometric interpretation.
As an application, some of these covariants are used to produce
explicit equations, inequations and inequalities defining the orbits
of projective quadratic parameterizations of quartic surfaces.

Conference Proceedings


 
Combinatorial proof for a stability property of plethysm coefficients.
Emmanuel Briand and Laura Colmenarejo.
Electronic Notes in Discrete Mathematics . Vol. 46.
Proceedings of the IX Jornadas de Matemática discreta y algoritmica (Tarragona, 911 july 2014).
Edited by Juan Alberto Rodríguez Velázquez and Ismael González Yero.
pp. 4350 (sept. 2014).
abstract


 
Generating vector partitions.
Emmanuel Briand.
Avances en Matemática Discreta en Andalucía. vol 2. VII encuentro andaluz de matemática discreta, ed. José Caceres, Clara Grima, Alberto Márquez, María Luz Puertas. Univ. de Almería, ISBN 9788469456279. pp. 1723 (2012).
abstract


 
The stability of the Kronecker product of Schur functions.
Emmanuel Briand, Rosa Orellana and Mercedes Rosas.
DMTCS Proceedings,
22nd International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2010), pp. 557568 (2010).
In the late 1930's Murnaghan discovered the existence of a stabilization phenomenon for the Kronecker product of Schur functions. For n large enough, the values of the Kronecker coefficients appearing in the product of two Schur functions of degree n do not depend on the first part of the indexing partitions, but only on the values of their remaining parts. We compute the exact value of n when this stable expansion is reached. We also compute two new bounds for the stabilization of a particular coefficient of such a product. Given partitions α and β, we give bounds for all the parts of any partition γ such that the corresponding Kronecker coefficient is nonzero. Finally, we also show that the reduced Kronecker coefficients are structure coefficients for the Heisenberg product introduced by Aguiar, Ferrer and Moreira.



 
Quasipolynomial formulas for the Kronecker coefficients indexed by two tworow shapes (extended abstract).
Emmanuel Briand, Rosa Orellana and Mercedes Rosas.
DMTCS Proceedings,
21st International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2009), pp. 241252 (2009).
We show that the Kronecker coefficients indexed by two tworow shapes are given by quadratic quasipolynomial formulas whose domains are the maximal cells of a fan. Simple calculations provide explicitly the quasipolynomial formulas and a description of the associated fan.
These new formulas are obtained from analogous formulas for the corresponding reduced Kronecker coefficients and a formula recovering the Kronecker coefficients from the reduced Kronecker coefficients.
As an application, we characterize all the Kronecker coefficients indexed by two tworow shapes that are equal to zero. This allowed us to disprove a conjecture of Mulmuley about the behavior of the
stretching functions attached to the Kronecker coefficients.


  
Reduced Kronecker coefficients.
Emmanuel Briand, Rosa Orellana and Mercedes Rosas.
Actas de los XI Encuentros de Algebra Computacional y Aplicaciones: EACA 2008 (Granada), pp. 101104.
We provide a formula that recovers the Kronecker coefficients (the multiplicities of the irreducible representations in the tensor products of two irreducible representations of the symmetric group) from the reduced Kronecker coefficients (limits of certain stationary sequences of Kronecker coefficients introduced by Murnaghan). This formula generalizes a formula due to Rosas for Kronecker coefficients indexed by two tworow shapes.
We use our formula to obtain a new stability bound for the Kronecker coefficients, and to describe explicitely the Kronecker coefficients indexed by two tworow shapes as a piecewise quasipolynomial, with the chambers of a fan as domains of quasipolynomiality.



 
Diagonally symmetric polynomials of the roots of some systems of polynomial equations .
Emmanuel Briand.
Actas de los X Encuentros de Algebra Computacional y Aplicaciones: EACA 2006 (Sevilla), 6164.
We present two situations in which the
diagonally symmetric
polynomials of the n roots of a system of polynomial equations
depend in a simple way on the coefficients of the equations: for
Gröbner bases with prescribed leading terms, and for zerodimensional
strict complete intersections. The results are independent on the
characteristic of the ground field.

  
Brill's equations for the subvariety of factorizable forms .
Emmanuel Briand.
Actas de los IX Encuentros de Algebra Computacional y Aplicaciones: EACA 2004 (Santander), 5963.
The products of n linear forms in N variables are a subvariety of the space of the forms of degree n in N variables. At the end of the nineteenth century, Brill and Gordan used invariant theory to design a method to derive a system of equations defining settheoretically this subvariety (Brill's equations).
We show how to compute efficiently Brill's equations, and compare them with the ideal of the subvariety.



Other texts


  
Une traduction de Das Zerfallen der Curven in
gerade Linien (Au sujet des courbes qui se décomposent en
lignes droites) de Paul Gordan.
Emmanuel Briand and Andreas Seidl.
2005.
This is a translation, form german to french, of Paul Gordan's 1894 paper Das Zerfallen
der Curven in gerade Linien (About the curves that decompose into straight lines).


  
Duality for couples of conics.
Emmanuel Briand.
2005, 10 pp.
Consider the couples of distinct proper nonempty real projective conics. A
rigid isotopy for such an object
is a continuous deformation of the defining equations of the two
conics, not modifying the singularity of the intersection points. Each class of rigid
isotopy corresponds to a ``configuration'' of a couple of conics.
In the present paper, we show that if two couples of conics are in the
same configuration, so are the corresponding couples of tangential
conics. We make explicit the induced bijection between the
configurations in the primal space and the configurations in the dual space.
