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Partial differential equations (PDEs): Existence and uniqueness, regularity, boundary conditions, linear and non-linear operators, stability, soliton theory, integrable PDEs, conservation laws, qualitative dynamics.

1 vote
0 answers
90 views

SPDE via fixed point argument and Young's theorem

Let $(P_r)_{r\geq 0}$ be a strongly continuous semi-group (not necessarily the heat kernel). It is well known that we can prove local well-posedness of a few SPDE using a fixed point argument: Young's …
mathex's user avatar
  • 573
6 votes
0 answers
240 views

Global well posedness of $\phi^4_1$

We consider the $\phi^4_1$ model: $\partial_t\phi=\Delta\phi-\phi^3+\xi$ on $[0,T] \times \mathbb{R},$ where $\xi$ is a space time white noise. I know how to solve this equation locally on the torus, …
mathex's user avatar
  • 573
4 votes
1 answer
205 views

Local solutions of renormalized stochastic PDE

To illustrate the problem consider the mild formulation of the $\Phi^4_2$ model on $[0,T]\times \mathbb{T}^d$: $$\phi=P_r\phi_0+\int_0^rP_{r-q}(-\phi^3(q))dq+Y_r \ \ \ \ \ \ (1)$$ where $(P_r)_{r \ge …
mathex's user avatar
  • 573
3 votes
0 answers
192 views

Towards Schauder estimates: smoothing effect of the semi-group generated by $\Delta+(-\Delta...

Consider the semi-group $(P_r)_r$ generated by $\Delta+(-\Delta)^{1/2}:$ for a distribution $f$ let $P_rf:=p(r,\cdot)*f$ where $p(r,x):=\sum_{q \in \mathbb{Z}^d}e^{2\pi\mathrm{i}\langle q,x\rangle}e^{ …
mathex's user avatar
  • 573
2 votes
0 answers
134 views

Towards the KPZ: Wiener-Ito integral, Kolmogorov type criterion

Consider a space-time white noise $\xi$ and the heat semi-group $(P_r).$ The following Kolmogorov type criterion allows to construct modifications in Besov Space (Here we have a partition of unity $(\ …
mathex's user avatar
  • 573
4 votes
0 answers
72 views

Regularity structures-paracontrolled distributions: do they always work for sub-critical SPDE?

Stochastic PDE could be solved using either regularity structures or paracontrolled distributions, as long it's sub-critical. I was wondering if this was proven, that is every sub-critical SPDE could …
mathex's user avatar
  • 573
1 vote
0 answers
87 views

Heat kernel and estimates

In the article by Hairer-Labbe (A simple construction of the continuum parabolic Anderson model on $\mathbb{R}^2$), they used the following "well known" fact (picture below) in holder spaces. I was w …
mathex's user avatar
  • 573
4 votes
0 answers
102 views

SPDE Renormalization

some SPDE (in higher dimensions) can only be interpreted in a "renormalised" sense. For example considering $\Phi_2^4$ on $\mathbb{R}_+\times \mathbb{T}^d$ the solution is defined as the limit of $\ph …
mathex's user avatar
  • 573
5 votes
1 answer
200 views

Continuity dependence and convergence of the renormalized $\Phi^4_2$ model

This question is continuous for the one asked here: Local solutions of renormalized stochastic PDE but it was better to ask it separetely. Again, we are interested in the local behavior of the $\Phi_2 …
mathex's user avatar
  • 573
2 votes
0 answers
118 views

Holder-Besov space and time continuity

Let $\mathbb{T}^d$ be the $d$-dimensional torus, $\mathscr{S}:=C^\infty(\mathbb{T}^d)$ the Schwartz space, $\mathscr{S}'$ the space of tempered distributions. We consider a dyadic partition of unity $ …
mathex's user avatar
  • 573
5 votes
0 answers
378 views

Is it really interesting to prove well-posedness of unsolved SPDE?

Lots of nonlinear SPDE remained open for decades (especially the non-deterministic ones in higher dimensions because of the regularity of the noise) until Hairer's breakthrough (regularity structures) …
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  • 573