## Publications

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Book
Bini, Dario, Torsten Ehrhardt, Alexei Yu. Karlovich, and Ilya M. Spitkovsky(eds.) Large Truncated Toeplitz Matrices, Toeplitz Operators, and Related Topics. The Albrecht Böttcher Anniversary Volume. Basel: Birkhäuser Basel, 2017.Website
Bastos, Maria Amélia, Luís Castro, and Alexei Yu. Karlovich(eds.) Operator Theory, Functional Analysis and Applications. Basel: Birkhäuser, 2020.
André, Carlos, Maria Amélia Bastos, Alexei Yu. Karlovich, Bernd Silbermann, and Ion Zaballa(Eds.) Operator Theory, Operator Algebras, and Matrix Theory. Basel: Birkhäuser, 2018.Website
Book Chapter
Karlovich, Alexei Yu. "Algebras of singular integral operators on Nakano spaces with Khvedelidze weights over Carleson curves with logarithmic whirl points." Izvestiya Vysshih Uchebnyh Zavedeniy. Severo-Kavkazskiy Region. Estestvennye Nauki. Special Issue "Pseudodifferential equations and some problems of mathematical physics". Rostov-on-Don: Rostov University Press, 2005. 135-142. Abstract22_2005_simonenko-70.pdf

We establish a Fredholm criterion for an arbitrary operator in the Banach algebra of singular integral operators
with piecewise continuous coefficients on Nakano spaces (generalized Lebesgue spaces with variable exponent) with Khvedelidze weights over Carleson curves with logarithmic whirl points.

Karlovich, Alexei Yu. "Algebras of singular integral operators with piecewise continuous coefficients on weighted Nakano spaces." The Extended Field of Operator Theory. Operator Theory: Advances and Applications, 171. Ed. Michael A. Dritschel. Basel: Birkhäuser, 2007. 171-188. Abstract

We find Fredholm criteria and a formula for the index of an arbitrary operator in the Banach algebra of singular integral operators with piecewise continuous coefficients on Nakano spaces (generalized Lebesgue spaces with variable exponent) with Khvedelidze weights over either Lyapunov curves or Radon curves without cusps. These results localize'' the Gohberg-Krupnik Fredhohn theory with respect to the variable exponent.

Karlovich, Alexei Yu. "Asymptotics of Toeplitz determinants generated by functions with Fourier coefficients in weighted Orlicz sequence classes." Function Spaces. Contemporary Mathematics, 435. Ed. K. Jarosz. Providence, RI: American Mathematical Society, 2007. 229-243. Abstract

We prove asymptotic formulas for Toeplitz determinants generated by functions with sequences of Fourier coefficients belonging to weighted Orlicz sequence classes. We concentrate our attention on the case of nonvanishing generating functions with nonzero Cauchy index.

Karlovich, Alexei Yu. "Asymptotics of Toeplitz matrices with symbols in some generalized Krein algebras." Modern Analysis and Applications: Mark Krein Centenary Conference, Vol. 1. Operator Theory Advances and Applications, 190. Eds. V. Adamyan, Y. Berezansky, I. Gohberg, M. Gorbachuk, V. Gorbachuk, A. Kochubei, H. Langer, and G. Popov. Basel: Birkhäuser, 2009. 341-359. Abstract

Let $$\alpha,\beta\in(0,1)$$ and
$K^{\alpha,\beta}:=\left\{a\in L^\infty(\mathbb{T}):\ \sum_{k=1}^\infty |\widehat{a}(-k)|^2 k^{2\alpha}<\infty,\ \sum_{k=1}^\infty |\widehat{a}(k)|^2 k^{2\beta}<\infty \right\}.$
Mark Krein proved in 1966 that $$K^{1/2,1/2}$$ forms a Banach algebra. He also observed that this algebra is important in the asymptotic theory of finite Toeplitz matrices. Ten years later, Harold Widom extended
earlier results of Gabor Szegö for scalar symbols and established the asymptotic trace formula
$\operatorname{trace}f(T_n(a))=(n+1)G_f(a)+E_f(a)+o(1) \quad\text{as}\ n\to\infty$
for finite Toeplitz matrices $$T_n(a)$$ with matrix symbols $$a\in K^{1/2,1/2}_{N\times N}$$. We show that if $$\alpha+\beta\ge 1$$ and $$a\in K^{\alpha,\beta}_{N\times N}$$, then the Szegö-Widom asymptotic trace formula holds with $$o(1)$$ replaced by $$o(n^{1-\alpha-\beta})$$.

Karlovich, Alexei Yu. "Boundedness of pseudodifferential operators on Banach function spaces." Operator Theory, Operator Algebras and Applications. Operator Theory: Advances and Applications, 242. Eds. Maria Amélia Bastos, Amarino Lebre, Stefan Samko, and Ilya M. Spitkovsky. Basel: Birkhäuser/Springer, 2014. 185-195. Abstract

We show that if the Hardy-Littlewood maximal operator is bounded on a separable Banach function space $$X(\mathbb{R}^n)$$ and on its associate space $$X'(\mathbb{R}^n)$$, then a pseudodifferential operator $$\operatorname{Op}(a)$$ is bounded on $$X(\mathbb{R}^n)$$ whenever the symbol $$a$$ belongs to the Hörmander class $$S_{\rho,\delta}^{n(\rho-1)}$$ with $$0<\rho\le 1$$, $$0\le\delta<1$$ or to the the Miyachi class $$S_{\rho,\delta}^{n(\rho-1)}(\varkappa,n)$$ with $$0\le\delta\le\rho\le 1$$, $$0\le\delta<1$$, and $$\varkappa>0$$. This result is applied to the case of variable Lebesgue spaces $$L^{p(\cdot)}(\mathbb{R}^n)$$.

Fernandes, Cláudio A., Alexei Yu. Karlovich, and Yuri I. Karlovich. "Calkin images of Fourier convolution operators with slowly oscillating symbols." Proceedings of IWOTA 2019. In Press.
Karlovich, Alexei Yu., and Ilya M. Spitkovsky. "The Cauchy singular integral operator on weighted variable Lebesgue spaces." Concrete Operators, Spectral Theory, Operators in Harmonic Analysis and Approximation. Operator Theory: Advances and Applications, 236. Eds. Manuel Cepedello Boiso, Håkan Hedenmalm, Marinus A. Kaashoek, Alfonso Montes Rodríguez, and Sergei Treil. Basel: Birkhäuser, 2014. 275-291. Abstract

Let $$p:\mathbb{R}\to(1,\infty)$$ be a globally log-Hölder continuous variable exponent and $$w:\mathbb{R}\to[0,\infty]$$ be a weight. We prove that the Cauchy singular integral operator $$S$$ is bounded on the weighted variable Lebesgue space $$L^{p(\cdot)}(\mathbb{R},w)=\{f:fw\in L^{p(\cdot)}(\mathbb{R})\}$$ if and only if the weight $$w$$ satisfies $$\sup_{-\infty < a < b < \infty} \frac{1}{b-a} \|w\chi_{(a,b)}\|_{p(\cdot)} \|w^{-1}\chi_{(a,b)}\|_{p'(\cdot)}<\infty \quad (1/p(x)+1/p'(x)=1).$$

Karlovich, Alexei Yu., and Yuri I. Karlovich. "Compactness of commutators arising in the Fredholm theory of singular integral operators with shifts." Factorization, Singular Operators and Related Problems. Eds. Stefan Samko, Amarino Lebre, and António Ferreira dos Santos. Dordrecht: Kluwer Academic Publishers, 2003. 111-129. Abstract

The paper is devoted to the compactness of the commutators $$aS_\Gamma - S_\Gamma aI$$ and $$W_\alpha S_\Gamma - S_\Gamma W_\alpha$$, where $$S_\Gamma$$ is the Cauchy singular integral operator, $$a$$ is a bounded measurable function, $$W_\alpha$$ is the shift operator given by $$W_\alpha f = f\circ\alpha$$, and $$\alpha$$ is a bi-Lipschitz homeomorphism (shift). The cases of the unit circle and the unit interval are considered. We prove that these commutators are compact on rearrangement-invariant spaces with nontrivial Boyd indices if and only if the function a or, respectively, the derivative of the shift a has vanishing mean oscillation.

Fernandes, Cláudio A., Alexei Yu. Karlovich, and Yuri I. Karlovich. "Fourier convolution operators with symbols equivalent to zero at infinity on Banach function spaces." Proceedings of ISAAC 2019. In Press.
Karlovich, Alexei Yu. "Higher order asymptotic formulas for traces of Toeplitz matrices with symbols in Hölder-Zygmund spaces." Recent Advances in Matrix and Operator Theory. Operator Theory: Advances and Applications, 179. Eds. Joseph A. Ball, Yuli Eidelman, William J. Helton, Vadim Olshevsky, and James Rovnyak. Basel: Bikhäuser, 2008. 185-196. Abstract

We prove a higher order asymptotic formula for traces of finite block Toeplitz matrices with symbols belonging to Hölder-Zygmund spaces. The remainder in this formula goes to zero very rapidly for very smooth symbols. This formula refines previous asymptotic trace formulas by Szegő and Widom and complement higher order asymptotic formulas for determinants of finite block Toeplitz matrices due to Böttcher and Silbermann.

Karlovich, Alexei Yu. "Higher-order asymptotic formulas for Toeplitz matrices with symbols in generalized Hölder spaces." Operator Algebra, Operator Theory and Applications. Operator Theory Advances and Applications, 181. Eds. MA Bastos, I. Gohberg, AB Lebre, and FO Speck. Basel: Birkhäuser, 2008. 207-228. Abstract

We prove higher-order asymptotic formulas for determinants and traces of finite block Toeplitz matrices generated by matrix functions belonging to generalized Hölder spaces with characteristic functions from the Bari-Stechkin class. We follow the approach of Böttcher and Silbermann and generalize their results for symbols in standard Hölder spaces.

Karlovich, Alexei Yu., and Yuri I. Karlovich. "Invertibility in Banach algebras of functional operators with non-Carleman shifts." Ukrains'kyj matematychnyj kongres -- 2001. Pratsi. Sektsiya 11. Funktsional'nyj analiz. Kyiv: Instytut Matematyky NAN Ukrainy, 2002. 107-124. Abstract13_2002_ukrainian_math_congress-kyiv-01.pdf

We prove the inverse closedness of the Banach algebra $$\mathfrak{A}_p$$ of functional operators with non-Carleman shifts, which have only two fixed points, in the Banach algebra of all bounded linear operators on $$L^p$$. We suppose that $$1 \le p \le \infty$$ and the generators of the algebra $$\mathfrak{A}_p$$ have essentially bounded data. An invertibility criterion for functional operators in $$\mathfrak{A}_p$$ is obtained in terms of
the invertibility of a family of discrete operators on $$l^p$$. An effective invertibility criterion is established for binomial difference operators with $$l^\infty$$ coefficients on the spaces $$l^p$$. Using the reduction to binomial difference operators, we give effective criteria of invertibility for binomial functional operators on the spaces $$L^p$$.

Karlovich, Alexei Yu., Yuri I. Karlovich, and Amarino B. Lebre. "Invertibility of functional operators with slowly oscillating non-Carleman shifts." Singular Integral Operators, Factorization and Applications. Operator Theory: Advances and Applications, 142. Eds. Albrecht Böttcher, Marinus A. Kaashoek, Amarino Brites Lebre, António Ferreira dos Santos, and Frank-Olme Speck. Basel: Birkhäuser, 2003. 147-174. Abstract

We prove criteria for the invertibility of the binomial functional operator
$A=aI-bW_\alpha$
in the Lebesgue spaces $$L^p(0,1)$$, $$1 < p < \infty$$, where $$a$$ and $$b$$ are continuous functions on $$(0,1)$$, $$I$$ is the identity operator, $$W_\alpha$$ is the shift operator, $$W_\alpha f=f\circ\alpha$$, generated by a non-Carleman shift $$\alpha:[0,1]\to[0,1]$$ which has only two fixed points $$0$$ and $$1$$. We suppose that $$\log\alpha'$$ is bounded and continuous on $$(0,1)$$ and that $$a,b,\alpha'$$ slowly oscillate at $$0$$ and $$1$$. The main difficulty connected with slow oscillation is overcome by using the method of limit operators.

Karlovich, Alexei Yu. "Maximally modulated singular integral operators and their applications to pseudodifferential operators on Banach function spaces." Function Spaces in Analysis. Contemporary Mathematics, 645. Ed. Krzysztof Jarosz. Providence, Rhode Island: American Mathematical Society, 2015. 165-178. Abstract

We prove that if the Hardy-Littlewood maximal operator is bounded on a separable Banach function space $$X(\mathbb{R}^n)$$ and on its associate space $$X'(\mathbb{R}^n)$$ and a maximally modulated Calderón-Zygmund singular integral operator $$T^{\Phi}$$ is of weak type $$(r,r)$$ for all $$r\in(1,\infty)$$, then $$T^{\Phi}$$ extends to a bounded operator on $$X(\mathbb{R}^n)$$. This theorem implies the boundedness of the maximally modulated Hilbert transform on variable Lebesgue spaces $$L^{p(\cdot)}(\mathbb{R})$$ under natural assumptions on the variable exponent $$p:\mathbb{R}\to(1,\infty)$$. Applications of the above result to the boundedness and compactness of pseudodifferential operators with $$L^\infty(\mathbb{R},V(\mathbb{R}))$$-symbols on variable Lebesgue spaces $$L^{p(\cdot)}(\mathbb{R})$$ are considered. Here the Banach algebra $$L^\infty(\mathbb{R},V(\mathbb{R}))$$ consists of all bounded measurable $$V(\mathbb{R})$$-valued functions on $$\mathbb{R}$$ where $$V(\mathbb{R})$$ is the Banach algebra of all functions of bounded total variation.

Karlovich, Alexei Yu., and Eugene Shargorodsky. "More on the density of analytic polynomials in abstract Hardy spaces." The Diversity and Beauty of Applied Operator Theory. Operator Theory: Advances and Applications, vol. 268. Eds. Albrecht Böttcher, Daniel Potts, Peter Stollman, and David Wenzel. Basel: Birkhäuser, 2018. 319-329.
Karlovich, Alexei Yu., and L. Maligranda. "On the interpolation constant for subadditive operators in Orlicz spaces." Proceedings of the International Symposium on Banach and Function Spaces II (ISBFS 2006), Kyushu Institute of Technology, Kitakyushu, Japan, 14-17 September 2006. Eds. M. Kato, and L. Maligranda. Yokohama: Yokohama Publishers, 2008. 85-101.
Karlovich, Alexei Yu., and Ilya M. Spitkovsky. "Pseudodifferential operators on variable Lebesgue spaces." Operator Theory, Pseudo-Differential Equations, and Mathematical Physics. Operator Theory: Advances and Applications, 228. Eds. Yuri I. Karlovich, Luigi Rodino, Bernd Silbermann, and Ilya M. Spitkovsky. Basel: Birkhäuser, 2013. 173-183. Abstract

Let $$\mathcal{M}(\mathbb{R}^n)$$ be the class of bounded away from one and infinity functions $$p:\mathbb{R}^n\to[1,\infty]$$ such that the Hardy-Littlewood maximal operator is bounded on the variable Lebesgue space $$L^{p(\cdot)}(\mathbb{R}^n)$$. We show that if $$a$$ belongs to the Hörmander class $$S_{\rho,\delta}^{n(\rho-1)}$$ with $$0<\rho\le 1$$, $$0\le\delta<1$$, then the pseudodifferential operator $$\operatorname{Op}(a)$$ is bounded on the variable Lebesgue space $$L^{p(\cdot)}(\mathbb{R}^n)$$ provided that $$p\in\mathcal{M}(\mathbb{R}^n)$$. Let $$\mathcal{M}^*(\mathbb{R}^n)$$ be the class of variable exponents $$p\in\mathcal{M}(\mathbb{R}^n)$$ represented as $$1/p(x)=\theta/p_0+(1-\theta)/p_1(x)$$ where $$p_0\in(1,\infty)$$, $$\theta\in(0,1)$$, and $$p_1\in\mathcal{M}(\mathbb{R}^n)$$. We prove that if $$a\in S_{1,0}^0$$ slowly oscillates at infinity in the first variable, then the condition $\lim_{R\to\infty}\inf_{|x|+|\xi|\ge R}|a(x,\xi)|>0$ is sufficient for the Fredholmness of $$\operatorname{Op}(a)$$ on $$L^{p(\cdot)}(\mathbb{R}^n)$$ whenever $$p\in\mathcal{M}^*(\mathbb{R}^n)$$. Both theorems generalize pioneering results by Rabinovich and Samko [RS08] obtained for globally log-Hölder continuous exponents $$p$$, constituting a proper subset of $$\mathcal{M}^*(\mathbb{R}^n)$$.

Karlovich, Alexei Yu., Yuri I. Karlovich, and Amarino B. Lebre. "Semi-Fredholmness of weighted singular integral operators with shifts and slowly oscillating data." Operator Theory, Operator Algebras, and Matrix Theory. Operator Theory: Advances and Applications, vol. 267. Eds. Carlos André, Maria Amélia Bastos, Alexei Yu. Karlovich, Bernd Silbermann, and Ion Zaballa. Basel: Birkhäuser, 2018. 221-246.
Karlovich, Alexei Yu. "Singular integral operators on Nakano spaces with weights having finite sets of discontinuities." Function spaces IX. Proceedings of the 9th international conference, Kraków, Poland, July 6–11, 2009. Banach Center Publications, 92. Eds. Henryk Hudzik, Grzegorz Lewicki, Julian Musielak, Marian Nowak, and Leszek Skrzypczak. Warszawa: Polish Academy of Sciences, Institute of Mathematics, 2011. 143-166. Abstract

In 1968, Gohberg and Krupnik found a Fredholm criterion for singular integral operators of the form $$aP+bQ$$, where $$a,b$$ are piecewise continuous functions and $$P,Q$$ are complementary projections associated to the Cauchy singular integral operator, acting on Lebesgue spaces over Lyapunov curves. We extend this result to the case of Nakano spaces (also known as variable Lebesgue spaces) with certain weights having finite sets of discontinuities on arbitrary Carleson curves.

Karlovich, Alexei Yu. "Singular integral operators on variable Lebesgue spaces over arbitrary Carleson curves." Topics in Operator Theory: Operators, Matrices and Analytic Functions, Vol. 1. Operator Theory: Advances and Applications, 202. Eds. JA Ball, V. Bolotnikov, JW Helton, L. Rodman, and IM Spitkovsky. Basel: Birkhäuser, 2010. 321-336. Abstract

In 1968, Israel Gohberg and Naum Krupnik discovered that local spectra of singular integral operators with piecewise continuous coefficients on Lebesgue spaces $$L^p(\Gamma)$$ over Lyapunov curves have the shape of circular arcs. About 25 years later, Albrecht Böttcher and Yuri Karlovich realized that these circular arcs metamorphose to so-called logarithmic leaves with a median separating point when Lyapunov curves metamorphose to arbitrary Carleson curves. We show that this result remains valid in a more general setting of variable Lebesgue spaces $$L^{p(\cdot)}(\Gamma)$$ where $$p:\Gamma\to(1,\infty)$$ satisfies the Dini-Lipschitz condition. One of the main ingredients of the proof is a new condition for the boundedness of the Cauchy singular integral operator on variable Lebesgue spaces with weights related to oscillations of Carleson curves.

Karlovich, Alexei Yu. "Singular integral operators on variable Lebesgue spaces with radial oscillating weights." Operator Algebras, Operator Theory and Applications.Operator Theory Advances and Applications, 195 . Eds. JJ Grobler, LE Labuschagne, and M. Möller. Basel: Birkhäuser, 2010. 185-212. Abstract

We prove a Fredholm criterion for operators in the Banach algebra of singular integral operators with matrix piecewise continuous coefficients acting on a variable Lebesgue space with a radial oscillating weight over a logarithmic Carleson curve. The local spectra of these operators are massive and have a shape of spiralic horns depending on the value of the variable exponent, the spirality indices of the curve, and the Matuszewska-Orlicz indices of the weight at each point. These results extend (partially) the results of A. Böttcher, Yu. Karlovich, and V. Rabinovich for standard Lebesgue spaces to the case of variable Lebesgue spaces.

Karlovich, Alexei Yu. "Singular integral operators with flip and unbounded coefficients on rearrangement-invariant spaces." Functional Analysis and its Applications. Proceedings of the international conference, dedicated to the 110th anniversary of Stefan Banach, Lviv National University, Lviv, Ukraine, May 28--31, 2002. Eds. V. Kadets, and W. Zelazko. Amsterdam: Elsevier, 2004. 123-131. Abstract

We prove Fredholm criteria for singular integral operators of the form
$P_++M_bP_-+M_uUP_-,$
where $$P_\pm$$ are the Riesz projections, $$U$$ is the flip operator, and $$M_b,M_u$$ are operators of multiplication by functions $$b,u$$, respectively, on a reflexive rearrangement-invariant space with nontrivial Boyd indices over the unit circle. We assume a priori that $$M_b$$ is bounded, but $$M_u$$ may be unbounded. The function $$u$$ belongs to a class of, in general, unbounded functions that relates to the Douglas algebra $$H^\infty+C$$.