AMD-Numbers, Compactness, Strict Singularity and the Essential Spectrum of Operators

2002 ◽  
Vol 9 (2) ◽  
pp. 227-270
Author(s):  
A. Castejón ◽  
E. Corbacho ◽  
V. Tarieladze
Keyword(s):  
Banach Space ◽  
Hilbert Space ◽  
Essential Spectrum ◽  
Hilbert Spaces ◽  
Single Point ◽  
Minimal Elements ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Finite Dimensional ◽  
The Family

Abstract For an operator 𝑇 acting from an infinite-dimensional Hilbert space 𝐻 to a normed space 𝑌 we define the upper AMD-number and the lower AMD-number as the upper and the lower limit of the net (δ(𝑇|𝐸))𝐸∈𝐹𝐷(𝐻), with respect to the family 𝐹𝐷(𝐻) of all finite-dimensional subspaces of 𝐻. When these numbers are equal, the operator is called AMD-regular. It is shown that if an operator 𝑇 is compact, then and, conversely, this property implies the compactness of 𝑇 provided 𝑌 is of cotype 2, but without this requirement may not imply this. Moreover, it is shown that an operator 𝑇 has the property if and only if it is superstrictly singular. As a consequence, it is established that any superstrictly singular operator from a Hilbert space to a cotype 2 Banach space is compact. For an operator 𝑇, acting between Hilbert spaces, it is shown that and are respectively the maximal and the minimal elements of the essential spectrum of , and that 𝑇 is AMD-regular if and only if the essential spectrum of |𝑇| consists of a single point.

scholarly journals Isometric Group Actions on Hilbert Spaces: Structure of Orbits

2008 ◽  
Vol 60 (5) ◽  
pp. 1001-1009 ◽  
Author(s):  
Yves de Cornulier ◽  
Romain Tessera ◽  
Alain Valette
Keyword(s):  
Hilbert Space ◽  
Nilpotent Group ◽  
Hilbert Spaces ◽  
Metabelian Group ◽  
Isometric Action ◽  
Finitely Generated ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Isometric Group Actions ◽  
Dense Orbits

AbstractOur main result is that a finitely generated nilpotent group has no isometric action on an infinite-dimensional Hilbert space with dense orbits. In contrast, we construct such an action with a finitely generated metabelian group.

scholarly journals Tomography in Abstract Hilbert Spaces

2006 ◽  
Vol 13 (03) ◽  
pp. 239-253 ◽  
Author(s):  
V. I. Man'ko ◽  
G. Marmo ◽  
A. Simoni ◽  
F. Ventriglia
Keyword(s):  
Hilbert Space ◽  
Quantum State ◽  
Trace Formula ◽  
Hilbert Spaces ◽  
Scalar Product ◽  
Linear Operators ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Dimensional Hilbert Space ◽  
Rank One

The tomographic description of a quantum state is formulated in an abstract infinite-dimensional Hilbert space framework, the space of the Hilbert-Schmidt linear operators, with trace formula as scalar product. Resolutions of the unity, written in terms of over-complete sets of rank-one projectors and of associated Gram-Schmidt operators taking into account their non-orthogonality, are then used to reconstruct a quantum state from its tomograms. Examples of well known tomographic descriptions illustrate the exposed theory.

On the Hyperinvariant Subspace Problem. IV

2008 ◽  
Vol 60 (4) ◽  
pp. 758-789 ◽  
Author(s):  
H. Bercovici ◽  
C. Foias ◽  
C. Pearcy
Keyword(s):  
Hilbert Space ◽  
Compact Operator ◽  
Essential Spectrum ◽  
Complete Lattice ◽  
Unit Disc ◽  
Diagonal Operator ◽  
Hyperinvariant Subspace ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Subspace Problem

AbstractThis paper is a continuation of three recent articles concerning the structure of hyperinvariant subspace lattices of operators on a (separable, infinite dimensional) Hilbert space . We show herein, in particular, that there exists a “universal” fixed block-diagonal operator B on such that if ε > 0 is given and T is an arbitrary nonalgebraic operator on , then there exists a compact operator K of norm less than ε such that (i) Hlat(T) is isomorphic as a complete lattice to Hlat(B + K) and (ii) B + K is a quasidiagonal, C00, (BCP)-operator with spectrum and left essential spectrum the unit disc. In the last four sections of the paper, we investigate the possible structures of the hyperlattice of an arbitrary algebraic operator. Contrary to existing conjectures, Hlat(T) need not be generated by the ranges and kernels of the powers of T in the nilpotent case. In fact, this lattice can be infinite.

scholarly journals Complementary Lagrangians in infinite dimensional symplectic Hilbert spaces

2005 ◽  
Vol 77 (4) ◽  
pp. 589-594 ◽  
Author(s):  
Paolo Piccione ◽  
Daniel V. Tausk
Keyword(s):  
Hilbert Space ◽  
Hilbert Spaces ◽  
Countable Family ◽  
Spectral Theorem ◽  
Dimensional Case ◽  
Infinite Dimensional ◽  
Finite Dimensional ◽  
Lagrangian Subspaces ◽  
Finite Dimensional Case ◽  
Adjoint Operators

We prove that any countable family of Lagrangian subspaces of a symplectic Hilbert space admits a common complementary Lagrangian. The proof of this puzzling result, which is not totally elementary also in the finite dimensional case, is obtained as an application of the spectral theorem for unbounded self-adjoint operators.

On the statistical estimation of the logarithmic derivative of a measure in a Hilbert space

2010 ◽  
Vol 17 (4) ◽  
pp. 741-747
Author(s):  
Elizbar Nadaraya ◽  
Grigol Sokhadze
Keyword(s):  
Hilbert Space ◽  
Statistical Estimation ◽  
Logarithmic Derivative ◽  
Observation Data ◽  
Independent Observation ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Finite Dimensional ◽  
Dimensional Hilbert Space ◽  
Approximating Sequence

Abstract We consider the problem of statistical estimation of the logarithmic derivative of a measure in an infinite-dimensional Hilbert space. It is shown that an approximating sequence of finite-dimensional estimates can be constructed for the unknown logarithmic derivative using independent observation data.

scholarly journals NON-UNIFORM HYPERBOLICITY FOR INFINITE DIMENSIONAL COCYCLES

2013 ◽  
Vol 13 (03) ◽  
pp. 1250026 ◽  
Author(s):  
MÁRIO BESSA ◽  
MARIA CARVALHO
Keyword(s):  
Hilbert Space ◽  
Probability Measure ◽  
Compact Hausdorff Space ◽  
Hausdorff Space ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Dimensional Hilbert Space ◽  
The Family ◽  
Uniform Hyperbolicity ◽  
Partially Hyperbolic

Let [Formula: see text] be an infinite dimensional Hilbert space, X a compact Hausdorff space and f : X → X a homeomorphism which preserves a Borel ergodic probability measure which is positive on non-empty open sets. We prove that non-uniformly Anosov cocycles are C0-dense in the family of partially hyperbolic cocycles with non-trivial unstable bundles.

scholarly journals MINIMUM UNCERTAINTY AND ENTANGLEMENT

2013 ◽  
Vol 27 (16) ◽  
pp. 1350068 ◽  
Author(s):  
N. D. HARI DASS ◽  
TABISH QURESHI ◽  
ADITI SHEEL
Keyword(s):  
Hilbert Spaces ◽  
Uncertainty Relation ◽  
Entangled State ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
System A ◽  
Finite Dimensional ◽  
Schmidt Rank ◽  
Heisenberg Uncertainty ◽  
Minimum Uncertainty

We address the question, does a system A being entangled with another system B, put any constraints on the Heisenberg uncertainty relation (or the Schrödinger–Robertson inequality)? We find that the equality of the uncertainty relation cannot be reached for any two noncommuting observables, for finite dimensional Hilbert spaces if the Schmidt rank of the entangled state is maximal. One consequence is that the lower bound of the uncertainty relation can never be attained for any two observables for qubits, if the state is entangled. For infinite-dimensional Hilbert space too, we show that there is a class of physically interesting entangled states for which no two noncommuting observables can attain the minimum uncertainty equality.

scholarly journals A Modified Halpern's Iterative Scheme for Solving Split Feasibility Problems

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Jitsupa Deepho ◽  
Poom Kumam
Keyword(s):  
Hilbert Space ◽  
Hilbert Spaces ◽  
Iterative Scheme ◽  
Split Feasibility Problem ◽  
Feasibility Problem ◽  
Strong Convergence Theorem ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
The Split Feasibility Problem ◽  
Split Feasibility

The purpose of this paper is to introduce and study a modified Halpern’s iterative scheme for solving the split feasibility problem (SFP) in the setting of infinite-dimensional Hilbert spaces. Under suitable conditions a strong convergence theorem is established. The main result presented in this paper improves and extends some recent results done by Xu (Iterative methods for the split feasibility problem in infinite-dimensional Hilbert space, Inverse Problem 26 (2010) 105018) and some others.

scholarly journals Изометрии действительных подпространств самосопряженных операторов в банаховых симметричных идеалах

2019 ◽  
Author(s):  
B.R. Aminov ◽  
V.I. Chilin
Keyword(s):  
Hilbert Space ◽  
Unitary Operator ◽  
Hermitian Operator ◽  
Uniform Norm ◽  
Compact Operators ◽  
Linear Isometry ◽  
Infinite Dimensional ◽  
Infinite Dimensional Hilbert Space ◽  
Finite Dimensional ◽  
Adjoint Operators

Let (mathcal C_E, cdot_mathcal C_E) be a Banach symmetric ideal of compact operators, acting in a complex separable infinite-dimensional Hilbert space mathcal H. Let mathcal C_Ehxin mathcal C_E : xx be the real Banach subspace of self-adjoint operators in (mathcal C_E, cdot_mathcal C_E). We show that in the case when (mathcal C_E, cdot_mathcal C_E) is a separable or perfect Banach symmetric ideal (mathcal C_E eq mathcal C_2) any skew-Hermitian operator H: mathcal C_Ehto mathcal C_Eh has the following form H(x)i(xa - ax) for same aain mathcal B(mathcal H) and for all xin mathcal C_Eh. Using this description of skew-Hermitian operators, we obtain the following general form of surjective linear isometries V:mathcal C_Eh to mathcal C_Eh. Let (mathcal C_E, cdot_mathcal C_E) be a separable or a perfect Banach symmetric ideal with not uniform norm, that is p_mathcal C_E 1 for any finite dimensional projection p inmathcal C_E with dim p(mathcal H)1, let mathcal C_E eq mathcal C_2, and let V: mathcal C_Eh to mathcal C_Eh be a surjective linear isometry. Then there exists unitary or anti-unitary operator u on mathcal H such that V(x)uxu orV(x)-uxu for all x in mathcal C_Eh.

Non-Isomorphic Non-Hyperfinite Factors

1969 ◽  
Vol 21 ◽  
pp. 1293-1308 ◽  
Author(s):  
Wai-Mee Ching
Keyword(s):  
Hilbert Space ◽  
Von Neumann Algebra ◽  
Crossed Product ◽  
Type Ii ◽  
Von Neumann ◽  
Infinite Dimensional ◽  
Type Iii ◽  
Infinite Dimensional Hilbert Space ◽  
Finite Dimensional ◽  
Dimensional Hilbert Space

A von Neumann algebra is called hyperfinite if it is the weak closure of an increasing sequence of finite-dimensional von Neumann subalgebras. For a separable infinite-dimensional Hilbert space the following is known: there exist hyperfinite and non-hyperfinite factors of type II1 (4, Theorem 16’), and of type III (8, Theorem 1); all hyperfinite factors of type Hi are isomorphic (4, Theorem 14); there exist uncountably many non-isomorphic hyperfinite factors of type III (7, Theorem 4.8); there exist two nonisomorphic non-hyperfinite factors of type II1 (10), and of type III (11). In this paper we will show that on a separable infinite-dimensional Hilbert space there exist three non-isomorphic non-hyperfinite factors of type II1 (Theorem 2), and of type III (Theorem 3).Section 1 contains an exposition of crossed product, which is developed mainly for the construction of factors of type III in § 3.

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