11 papers
Fejér-Rogosinski theorem for the Neil algebra
Nilanjan Das, Jaydeb Sarkar
Partial sums of the Taylor expansions of functions from the Neil algebra are uniformly bounded by their uniform norms on the ball of radius centered at the origin, where de…
Invariant subspaces of Jordan blocks of
Sneha B, Jaydeb Sarkar, Michio Seto
It is known that invariant subspaces of classical Jordan blocks of the Hardy space over the open unit disc are described by factorizations of inner functions. In the polydisc setti…
Hyponormal contractions and analytic shifts
Sneha B, Neeru Bala, Jaydeb Sarkar
Hyponormal operators are known to be among the most difficult operators to analyze. In this work, we focus on two finite types of hyponormal operators. The first type becomes analy…
Foguel-type operators similar to contractions
Nilanjan Das, Soma Das, Jaydeb Sarkar
Pisier's celebrated counterexample to Halmos's similarity-to-contractions problem was based on upper triangular block operator matrices involving three classical opera…
New norm estimate for composition operators
Preeti Kumari, P. Muthukumar, Jaydeb Sarkar
The classical Littlewood's theorem establishes boundedness and provides a norm estimate for composition operators on the Hardy space. In this paper, we offer an alternative proof o…
Invariant subspaces of Brownian shifts on vector-valued Hardy spaces
Nilanjan Das, Soma Das, Jaydeb Sarkar
We characterize invariant subspaces of Brownian shifts on vector-valued Hardy spaces. We also solve the unitary equivalence problem for the invariant subspaces of these shifts.
Finite-dimensional model spaces invariant under composition operators
P. Muthukumar, Jaydeb Sarkar, Batzorig Undrakh
Finite-dimensional model spaces are quotient spaces of the Hardy space on the open unit disc, determined by finite Blaschke products. Composition operators, on the other hand, act…
Invariant subspaces and the -property of Brownian Shifts
Nilanjan Das, Soma Das, Jaydeb Sarkar
We consider the restriction of Brownian shifts to their invariant subspaces and classify when they are unitarily equivalent. Additionally, we prove an asymptotic property stating t…
Invariant subspaces of perturbed backward shift
Soma Das, Jaydeb Sarkar
We represent closed subspaces of the Hardy space that are invariant under finite-rank perturbations of the backward shift. We apply this to classify almost invariant subspaces of t…
Liftings and invariant subspaces of Hankel operators
Sneha B, Neeru Bala, Samir Panja +1
We prove a Hankel-variant commutant lifting theorem. This also uncovers the complete structure of the Beurling-type reducing and invariant subspaces of Hankel operators. Kernel spa…
Paired and Toeplitz + Hankel operators
Nilanjan Das, Soma Das, Jaydeb Sarkar
We present complete classifications of Toeplitz + Hankel operators on vector-valued Hardy spaces and classify paired operators on . We also study the latter class…