We provide a simple extension of Bolthausens Morita type proof cite{Bolt2} of the replica symmetric formula for the Sherrington-Kirkpatrick (SK) model and prove the replica symmetry for all $(beta,h)$ that satisfy $beta^2 E, text{sech}^2(betasqrt{q}Z
+h) leq 1$, where $q = Etanh^2(betasqrt{q}Z+h)$. Compared to cite{Bolt2}, the key of the argument is to apply the conditional second moment method to a suitably reduced partition function.
We derive mean-field equations for a general class of ferromagnetic spin systems with an explicit error bound in finite volumes. The proof is based on a link between the mean-field equation and the free convolution formalism of random matrix theory,
which we exploit in terms of a dynamical method. We present three sample applications of our results to Ka{c} interactions, randomly diluted models, and models with an asymptotically vanishing external field.
We present a new dynamical proof of the Thouless-Anderson-Palmer (TAP) equations for the classical Sherrington-Kirkpatrick spin glass at sufficiently high temperature. In our derivation, the TAP equations are a simple consequence of the decay of the
two point correlation functions. The methods can also be used to establish the decay of higher order correlation functions. We illustrate this by proving a suitable decay bound on the three point functions from which we derive an analogue of the TAP equations for the two point functions.
We consider N bosons in a box with volume one, interacting through a two-body potential with scattering length of the order $N^{-1+kappa}$, for $kappa>0$. Assuming that $kappain (0;1/43)$, we show that low-energy states of the system exhibit complete
Bose-Einstein condensation by providing explicit bounds on the expectation and on higher moments of the number of excitations.
We consider a system of $N$ bosons interacting through a singular two-body potential scaling with $N$ and having the form $N^{3beta-1} V (N^beta x)$, for an arbitrary parameter $beta in (0,1)$. We provide a norm-approximation for the many-body evolut
ion of initial data exhibiting Bose-Einstein condensation in terms of a cubic nonlinear Schrodinger equation for the condensate wave function and of a unitary Fock space evolution with a generator quadratic in creation and annihilation operators for the fluctuations.
We study the time-evolution of initially trapped Bose-Einstein condensates in the Gross-Pitaevskii regime. Under a physically motivated assumption on the energy of the initial data, we show that condensation is preserved by the many-body evolution an
d that the dynamics of the condensate wave function can be described by the time-dependent Gross-Pitaevskii equation. With respect to previous works, we provide optimal bounds on the rate of condensation (i.e. on the number of excitations of the Bose-Einstein condensate). To reach this goal, we combine the method of cite{LNS}, where fluctuations around the Hartree dynamics for $N$-particle initial data in the mean-field regime have been analyzed, with ideas from cite{BDS}, where the evolution of Fock-space initial data in the Gross-Pitaevskii regime has been considered.
