Bilinear smoothing conjecture for Fourier integral operators

Let d2d\geq2. Let Taϕ1,ϕ2T_a^{\phi_1,\phi_2} be a bilinear Fourier integral operator whose non-degenerate phase functions satisfy the cinematic curvature condition, and let aS1,0ma\in S^m_{1,0} be compactly supported in (x,t)Rd×R(x,t)\in\mathbb{R}^d\times\mathbb{R}, of order m<0m<0. Define

1p=1p1+1p2,m=m1+m2,\frac1p=\frac1{p_1}+\frac1{p_2},\qquad m=m_1+m_2,

with m10m_1\leq0 and m2<0m_2<0. Bilinear smoothing conjecture for FIOs. For p1,p2pdp_1,p_2\geq\overline p_d and σi<1pi\sigma_i<\frac1{p_i}, one has

Taϕ1,ϕ2(f,g)Lp(Rd×R)fLs1p1(Rd)gLs2p2(Rd),\lVert T_a^{\phi_1,\phi_2}(f,g)\rVert_{L^p(\mathbb{R}^d\times\mathbb{R})}\lesssim \lVert f\rVert_{L^{p_1}_{s_1}(\mathbb{R}^d)}\lVert g\rVert_{L^{p_2}_{s_2}(\mathbb{R}^d)},

where

si=mi+(d1)(121pi)σi.s_i=m_i+(d-1)\left(\frac12-\frac1{p_i}\right)-\sigma_i.

This is proposed as the bilinear analogue of the linear local smoothing conjecture in dimensions d2d\geq2; the supplied text gives no evidence that it has been resolved.

Sources & referencesView supporting material

Primary source

Duván Cardona, “Local smoothing estimates for bilinear Fourier integral operators”, arXiv:2601.15667 (2026).

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