## The Weyl calculus with locally temperate metric and weights.(English)Zbl 0621.47045

We extend the Weyl calculus of L. Hörmander [Commun. Pure Appl. Math. 32, 359-443 (1979; Zbl 0388.47032)] to symbols in $$T^*{\mathbb{R}}^ n$$, which are temperate in the $$\xi$$ variables. Thus they may grow exponentially in the x variables. In order to do that, we introduce a metric in the x variables, to define neighborhoods over which the symbols are temperate. We use cut-off functions $$\chi$$ supported in the corresponding neighborhood of the diagonal, to define the operators $a^ w_{\chi}(x,D)u(x)=(2\pi)^{-n}\iint e^{<x-y,\xi >}\chi (x,y)a(\frac{x+y}{2},\xi)u(y)dyd\xi,\quad u\in C_ 0^{\infty}({\mathbb{R}}^ n),$ where a(x,$$\xi)$$ is locally temperate. This generalizes V. I. Feijgin’s definition [Trudy Mosk. Mat. O.- va. 36, 155-194 (1978; Zbl 0421.35083)], and is independent of the choice of $$\chi$$ modulo terms of arbitrary low order, if $$\chi\equiv 1$$ in a neighborhood of the diagonal. We develop a calculus for these operators and show that they are continuous in $$C_ 0^{\infty}$$ and $${\mathcal D}'$$. We prove $$L^ 2$$-continuity when the symbol is bounded, and compactness when the symbol vanishes at $$\infty$$. The Hilbert-Schmidt norm of the operator is bounded by the $$L^ 2$$-norm of the symbol, and we prove an estimate on the trace class norm.
Finally, we give an application of the calculus by improving and generalizing V. I. Feijgin’s estimate [Math. Sb., n. Ser. 99(141), 594-614 (1976; Zbl 0336.35079)] of the error term in the Weyl formula of the number N($$\lambda)$$ of eigenvalues $$\leq \lambda$$ of certain self- adjoint $$p^ w_{\chi}$$ in $${\mathbb{R}}^ n$$, $N(\lambda)\sim (2\pi)^{-n}\iint_{p(x,\xi)\leq \lambda}dxd\xi,$ in the same way L. Hörmander [Ark. Mat. 17, 297-313 (1979; Zbl 0436.35064)] improved the estimate of V. N. Tulovskij and M. A. Shubin [Mat. Sb. n. Ser. 92(134), 571-588 (1973; Zbl 0286.35059)]. One example is the Laplacean with an exponentially growing real potential. For some temperated symbol classes sharper estimates for the error term are known, see V. I. Feijgin [Funkts. Anal. Prilozh. 16, No.3, 88-89 (1982; Zbl 0509.35077)] and references there.
Non-temperature metrics and weights also appear in higher order micro- localizations. For a more refined calculus for these symbol classes, see J. M. Bony and N. Lerner [Sém. éq. aux dér. part. 1986- 1987, No.2 and 3, École Polytechnique].

### MSC:

 47Gxx Integral, integro-differential, and pseudodifferential operators 35S05 Pseudodifferential operators as generalizations of partial differential operators 35P20 Asymptotic distributions of eigenvalues in context of PDEs 47B10 Linear operators belonging to operator ideals (nuclear, $$p$$-summing, in the Schatten-von Neumann classes, etc.)
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### References:

 [1] Beals, R. andFefferman, C., Spatially Inhomogeneous Pseudodifferential Operators I,Comm. Pure Appl. Math.,27 (1974), 1–24. · Zbl 0279.35071 [2] Beals, R., Spatially Inhomogeneous Pseudodifferential Operators II,Comm. Pure Appl. Math.,27 (1974), 161–205. · Zbl 0283.35071 [3] Beals, R., A general calculus of pseudodifferential operators,Duke Math. J.,42 (1975), 1–42. · Zbl 0343.35078 [4] Feigin, V. I., Asymptotic distribution of eigenvalues for hypoelliptic systems inR n. ,Mat. Sbornik,99 (141) (1976), 594–614 (Russian). English translation inMath. USSR Sbornik,28 (1976), 533–552. [5] Feigin, V. I., New classes of pseudodifferential operators inR n and some applications,Trudy Moskov. Mat., Obshch.,36 (1978), 155–194 (Russian). English translation inTrans. Moscov Math Soc.,36 (1978), 153–195. [6] Feigin, V. I., Sharp estimates of the remainder in the spectral asymptotic for pseudodifferential operators inR n. ,Funktsional. Anal. i Prilozhen.,16 (1982), 88–89 (Russian). English translation inFunctional Anal. Appl.,16 (1982), 233–235. · Zbl 0505.58031 [7] Hörmander, L., The Weyl Calculus of Pseudodifferential Operators,Comm. Pure Appl. Math.,32 (1979), 359–443. · Zbl 0396.47029 [8] Hörmander, L., On the asymptotic distribution of the eigenvalues of pseudodifferential operators inR n ,Ark. Mat.,17 (1979), 297–313. · Zbl 0436.35064 [9] Tulovskii, V. N. andŜubin, M. A., On the asymptotic distribution of eigenvalues of pseudodifferential operators inR n ,Mat. Sbornik,92 (134) (1973), 571–588 (Russian). English translation inMath. USSR Sbornik,21 (1973), 565–583.
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