8 research outputs found
Discriminants, symmetrized graph monomials, and sums of squares
Motivated by the necessities of the invariant theory of binary forms J. J.
Sylvester constructed in 1878 for each graph with possible multiple edges but
without loops its symmetrized graph monomial which is a polynomial in the
vertex labels of the original graph. In the 20-th century this construction was
studied by several authors. We pose the question for which graphs this
polynomial is a non-negative resp. a sum of squares. This problem is motivated
by a recent conjecture of F. Sottile and E. Mukhin on discriminant of the
derivative of a univariate polynomial, and an interesting example of P. and A.
Lax of a graph with 4 edges whose symmetrized graph monomial is non-negative
but not a sum of squares. We present detailed information about symmetrized
graph monomials for graphs with four and six edges, obtained by computer
calculations
Low temperature magnetic phase diagram of the cubic non-Fermi liquid system CeIn_(3-x)Sn_x
In this paper we report a comprehensive study of the magnetic susceptibility
(\chi), resistivity (\rho), and specific heat (C_P), down to 0.5 K of the cubic
CeIn_(3-x)Sn_x alloy. The ground state of this system evolves from
antiferromagnetic (AF) in CeIn_3(T_N=10.2 K) to intermediate-valent in CeSn_3,
and represents the first example of a Ce-lattice cubic non-Fermi liquid (NFL)
system where T_N(x) can be traced down to T=0 over more than a decade of
temperature. Our results indicate that the disappearance of the AF state occurs
near x_c ~ 0.7, although already at x ~ 0.4 significant modifications of the
magnetic ground state are observed. Between these concentrations, clear NFL
signatures are observed, such as \rho(T)\approx \rho_0 + A T^n (with n<1.5) and
C_P(T)\propto -T ln(T) dependencies. Within the ordered phase a first order
phase transition occurs for 0.25 < x < 0.5. With larger Sn doping, different
weak \rho(T) dependencies are observed at low temperatures between x=1 and x=3
while C_P/T shows only a weak temperature dependence.Comment: 7 pages, 7 figures. Accepted in Eur. J. Phys.