# Modified scattering for the critical nonlinear Schr\"odinger equation

## TL;DR

This paper analyzes the long-time behavior of solutions to the critical nonlinear Schr"odinger equation, constructing global solutions with specific decay rates and asymptotic expansions, using pseudo-conformal transformations and Sobolev norm estimates.

## Contribution

It introduces a class of initial data leading to global solutions with precise decay and asymptotic profiles, addressing regularity issues at zero and employing novel analytical techniques.

## Key findings

- Constructed solutions with decay like t^{-N/2} or (t log t)^{-N/2}
- Provided asymptotic expansions for these solutions
- Developed methods to handle non-vanishing solutions and regularity challenges

## Abstract

We consider the nonlinear Schr\"odinger equation $iu_t + \Delta u= \lambda |u|^{\frac {2} {N}} u $ in all dimensions $N\ge 1$, where $\lambda \in {\mathbb C}$ and $\Im \lambda \le 0$. We construct a class of initial values for which the corresponding solution is global and decays as $t\to \infty $, like $t^{- \frac {N} {2}}$ if $\Im \lambda =0$ and like $(t \log t)^{- \frac {N} {2}}$ if $\Im \lambda <0$. Moreover, we give an asymptotic expansion of those solutions as $t\to \infty $. We construct solutions that do not vanish, so as to avoid any issue related to the lack of regularity of the nonlinearity at $u=0$. To study the asymptotic behavior, we apply the pseudo-conformal transformation and estimate the solutions by allowing a certain growth of the Sobolev norms which depends on the order of regularity through a cascade of exponents.