<p>In this work, one proves the well-posedness in the Sobolev space <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(H^{-1}({\mathbb {R}^d})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>H</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of the Cauchy problem <Equation ID="Equ97"> <EquationSource Format="TEX">\(\begin{array}{r} \displaystyle \frac{{\partial }u}{{\partial }t}-\Delta \beta (u)+\textrm{div }((D(x)b(u)+K*u)u)=0 \\ \text{ in } (0,{\infty })\times {\mathbb {R}^d}; u(0,x)=u_0(x),\end{array}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="right"> <mstyle displaystyle="true" scriptlevel="0"> <mrow> <mfrac> <mrow> <mi>∂</mi> <mi>u</mi> </mrow> <mrow> <mi>∂</mi> <mi>t</mi> </mrow> </mfrac> <mo>-</mo> <mi mathvariant="normal">Δ</mi> <mi>β</mi> <mrow> <mo stretchy="false">(</mo> <mi>u</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mtext>div</mtext> <mspace width="0.333333em" /> <mrow> <mo stretchy="false">(</mo> <mrow> <mo stretchy="false">(</mo> <mi>D</mi> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mi>b</mi> <mrow> <mo stretchy="false">(</mo> <mi>u</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mi>K</mi> <mrow /> <mo>∗</mo> <mi>u</mi> <mo stretchy="false">)</mo> </mrow> <mi>u</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mn>0</mn> </mrow> </mstyle> </mtd> </mtr> <mtr> <mtd columnalign="right"> <mrow> <mrow /> <mspace width="0.333333em" /> <mtext>in</mtext> <mspace width="0.333333em" /> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mi>∞</mi> <mo stretchy="false">)</mo> </mrow> <mo>×</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> <mo>;</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>u</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(d\ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\beta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>β</mi> </math></EquationSource> </InlineEquation> is a continuous monotonically increasing function, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(D:{\mathbb {R}^d}\rightarrow {\mathbb {R}^d}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>D</mi> <mo>:</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> <mo stretchy="false">→</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(b:{\mathbb {R}}\rightarrow {\mathbb {R}}^+\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>b</mi> <mo>:</mo> <mi mathvariant="double-struck">R</mi> <mo stretchy="false">→</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mo>+</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> are appropriate functions and <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(K\!\in \! C^1({\mathbb {R}^d}\!\setminus \!0)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mspace width="-0.166667em" /> <mo>∈</mo> <mspace width="-0.166667em" /> <msup> <mi>C</mi> <mn>1</mn> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> <mspace width="-0.166667em" /> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mspace width="-0.166667em" /> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is a singular kernel. One proves also the uniqueness of distributional solutions <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(u\in L^1\cap L^{\infty }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>u</mi> <mo>∈</mo> <msup> <mi>L</mi> <mn>1</mn> </msup> <mo>∩</mo> <msup> <mi>L</mi> <mi>∞</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> which are weakly (narrowly) continuous in <i>t</i> from <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\([0,{\infty })\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">[</mo> <mn>0</mn> <mo>,</mo> <mi>∞</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> to <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(L^1({\mathbb {R}^d})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>L</mi> <mn>1</mn> </msup> <mrow> <mo stretchy="false">(</mo> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and the uniqueness for the corresponding linearized equations, As a consequence, it follows the existence and uniqueness of strong solutions to the McKean–Vlasov stochastic differential equation (SDE) <Equation ID="Equ98"> <EquationSource Format="TEX">\(\begin{array}{l} dX_t=(D(X)b(u(t,X_t)+(K*u(t,\cdot ))(X_t))dt +\left( \displaystyle \frac{2\beta (u(t,X_t))}{u(t,X_t)}\right) ^{\!\!\frac{1}{2}}dW_t\\ {\mathcal {L}}_{X_t}(x)=u(t,x),\ X(0)=X_0,\ u_0=\mathbb {P}\circ X^{-1}_0, \end{array}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <mtable> <mtr> <mtd columnalign="left"> <mrow> <mi>d</mi> <msub> <mi>X</mi> <mi>t</mi> </msub> <mrow> <mo>=</mo> <mo stretchy="false">(</mo> <mi>D</mi> <mrow> <mo stretchy="false">(</mo> <mi>X</mi> <mo stretchy="false">)</mo> </mrow> <mi>b</mi> </mrow> <mrow> <mo stretchy="false">(</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <msub> <mi>X</mi> <mi>t</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mrow> <mo stretchy="false">(</mo> <mi>K</mi> <mrow /> <mo>∗</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mo>·</mo> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mrow> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>t</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mi>d</mi> <mi>t</mi> <mo>+</mo> <msup> <mfenced close=")" open="("> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mrow> <mn>2</mn> <mi>β</mi> <mo stretchy="false">(</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <msub> <mi>X</mi> <mi>t</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mrow> <mi>u</mi> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <msub> <mi>X</mi> <mi>t</mi> </msub> <mo stretchy="false">)</mo> </mrow> </mfrac> </mstyle> </mfenced> <mrow> <mspace width="-0.166667em" /> <mspace width="-0.166667em" /> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </msup> <mi>d</mi> <msub> <mi>W</mi> <mi>t</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd columnalign="left"> <mrow> <mrow /> <msub> <mi mathvariant="script">L</mi> <msub> <mi>X</mi> <mi>t</mi> </msub> </msub> <mrow> <mo stretchy="false">(</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>u</mi> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mspace width="4pt" /> <mi>X</mi> <mrow> <mo stretchy="false">(</mo> <mn>0</mn> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msub> <mi>X</mi> <mn>0</mn> </msub> <mo>,</mo> <mspace width="4pt" /> <msub> <mi>u</mi> <mn>0</mn> </msub> <mo>=</mo> <mi mathvariant="double-struck">P</mi> <mo>∘</mo> <msubsup> <mi>X</mi> <mn>0</mn> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <mo>,</mo> </mrow> </mtd> </mtr> </mtable> </mrow> </math></EquationSource> </Equation>where <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\({\mathcal {L}}(X_t)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">L</mi> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>t</mi> </msub> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is the density of the probability law of the process <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(X_t\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>X</mi> <mi>t</mi> </msub> </math></EquationSource> </InlineEquation> with respect to the Lebesgue measure on <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\({\mathbb {R}^d}\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="double-struck">R</mi> </mrow> <mi>d</mi> </msup> </math></EquationSource> </InlineEquation>. Moreover, the laws of solutions to this equation have the Markov property.</p>

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Nonlinear Fokker–Planck equations with singular integral drifts and McKean–Vlasov SDEs

  • Viorel Barbu

摘要

In this work, one proves the well-posedness in the Sobolev space \(H^{-1}({\mathbb {R}^d})\) H - 1 ( R d ) of the Cauchy problem \(\begin{array}{r} \displaystyle \frac{{\partial }u}{{\partial }t}-\Delta \beta (u)+\textrm{div }((D(x)b(u)+K*u)u)=0 \\ \text{ in } (0,{\infty })\times {\mathbb {R}^d}; u(0,x)=u_0(x),\end{array}\) u t - Δ β ( u ) + div ( ( D ( x ) b ( u ) + K u ) u ) = 0 in ( 0 , ) × R d ; u ( 0 , x ) = u 0 ( x ) , where \(d\ge 2\) d 2 , \(\beta \) β is a continuous monotonically increasing function, \(D:{\mathbb {R}^d}\rightarrow {\mathbb {R}^d}\) D : R d R d , \(b:{\mathbb {R}}\rightarrow {\mathbb {R}}^+\) b : R R + are appropriate functions and \(K\!\in \! C^1({\mathbb {R}^d}\!\setminus \!0)\) K C 1 ( R d \ 0 ) is a singular kernel. One proves also the uniqueness of distributional solutions \(u\in L^1\cap L^{\infty }\) u L 1 L which are weakly (narrowly) continuous in t from \([0,{\infty })\) [ 0 , ) to \(L^1({\mathbb {R}^d})\) L 1 ( R d ) and the uniqueness for the corresponding linearized equations, As a consequence, it follows the existence and uniqueness of strong solutions to the McKean–Vlasov stochastic differential equation (SDE) \(\begin{array}{l} dX_t=(D(X)b(u(t,X_t)+(K*u(t,\cdot ))(X_t))dt +\left( \displaystyle \frac{2\beta (u(t,X_t))}{u(t,X_t)}\right) ^{\!\!\frac{1}{2}}dW_t\\ {\mathcal {L}}_{X_t}(x)=u(t,x),\ X(0)=X_0,\ u_0=\mathbb {P}\circ X^{-1}_0, \end{array}\) d X t = ( D ( X ) b ( u ( t , X t ) + ( K u ( t , · ) ) ( X t ) ) d t + 2 β ( u ( t , X t ) ) u ( t , X t ) 1 2 d W t L X t ( x ) = u ( t , x ) , X ( 0 ) = X 0 , u 0 = P X 0 - 1 , where \({\mathcal {L}}(X_t)\) L ( X t ) is the density of the probability law of the process \(X_t\) X t with respect to the Lebesgue measure on \({\mathbb {R}^d}\) R d . Moreover, the laws of solutions to this equation have the Markov property.