Stochastic dynamics from O(2N) fractional Laplacian vector model and O(N) vector model free energy in finite temperature

Abstract

We explore O(2N) vector model with fractional Laplacian, $\sqrt{-\nabla^2}$ in $d$-dimension and its Hamiltonain dynamics which is described by a Schrodinger type equation. This equation is a kind of current conservation equation, where one can define a current $j(ϕ^a)$ of a probability $P(ϕ^a)$, where $ϕ^a$ is the O(2N) vector field. Naturally, Gibbs entropy $S=-\int [Dϕ^a] P(ϕ^a)\log P(ϕ^a)$ can be considered to explore the system. We realize that this Gibbs entropy of the O(2N) vector model with fractional Laplacian is matched with free energy of O(N) vector model in finite temperature, $1/β$ with a deformation, $μ$ in $d$-dimension. The precise map between the stochastic fictitious time $t$ and the inverse temperature $β$ is $β=2t$. Therefore, the temperature dependence of the thermal O(N) vector model can be realized as a dynamics of time dependent solution satisfying Schrodinger type equation. This free energy is obtained by putting O(N) vector model in $S^1\times \mathbb R_d$, where $S^1$ is thermal circle with its periodicity $β$. To get $d$-dimensional theory, we sum up all possible frequencies on the circle(so called Matsubara frequency summation) which gives $d$-dimensional thermal partition function. We note that the nontrivial $t$-dependence appears beyond classical limit. To take into account quantum effects, we solve the Hamiltonian dynamics by keeping $\hbar$ corrections. The spectral deformation is mediated by a parameter $l$ such that $μ=β^{-1}\log l$ and so we call this $l$-deformation. This is related to the initial boundary condition of the Schrodinger equation. We also note that the two theoreis are not equivalent each other and we just check their correspondence in the level of one-loop determinant, i.e. zero point function in the note.