Commutative Variables Research Articles

The inverse of a quantum bilinear form of the oriented braid arrangement

We follow here the results of Varchenko, who assigned to each weighted arrangement \(\mathcal{A}\) of hyperplanes in the \(n\)-dimensional real space a bilinear form, which he called the quantum bilinear form of the arrangement \(\mathcal{A}\). We briefly explain the quantum bilinear form of the oriented braid arrangement in the \(n\)-dimensional real space. The main concern of this paper is to compute the inverse of the matrix of the quantum bilinear form of the oriented braid arrangement in \(\mathbb{R}^n\), \({n\ge 2}\). To solve this problem, in [3] the authors used some special matrices and their factorizations in terms of simpler matrices. So, to simplify some matrix calculations, we first introduce a twisted group algebra \({\mathcal{A}(S_{n})}\) of the symmetric group \(S_{n}\) with coefficients in the polynomial ring in \(n^2\) commutative variables and then use a natural representation of some elements of the algebra \({\mathcal{A}(S_{n})}\) on the generic weight subspaces of the multiparametric quon algebra \({\mathcal{B}}\), which immediately gives the corresponding matrices of the quantum bilinear form.

A noncommutative Bianchi I model with radiation

In this work, we study the dynamical evolution of a homogeneous and anisotropic, noncommutative (NC) Bianchi I (BI) model coupled to a radiation perfect fluid. Our first motivation is determining if the present model tends to a homogeneous and isotropic NC Friedmann–Robertson–Walker (FRW) model, during its evolution. In order to simplify our task, we use the Misner parametrization of the BI metric. In terms of that parametrization the BI metric has three metric functions: the scale factor [Formula: see text] and the two parameters [Formula: see text], which measure the spatial anisotropy of the model. Our second motivation is trying to describe the present accelerated expansion of the universe using noncommutativity (NCTY). The NCTY is introduced by two nontrivial Poisson brackets between some geometrical as well as matter variables of the model. We recover the description in terms of commutative variables by introducing some variables transformations that depend on the NC parameter. Using those variables’ transformations, we rewrite the total NC Hamiltonian of the model in terms of commutative variables. From the resulting Hamiltonian, we obtain the dynamical equations for a generic perfect fluid. In order to solve these equations, we restrict our attention to a model in which the perfect fluid is radiation. We solve, numerically, these equations and compare the NC solutions to the corresponding commutative ones. The comparison shows that the NC model may be considered as a possible candidate for describing the accelerated expansion of the universe. Finally, we obtain estimates for the NC parameter and compare the main results of the NC BI model coupled to radiation with the same NC BI model coupled to other perfect fluids. As our main result, we show that the solutions, after some time, produce an isotropic universe. Based on that result, we can speculate that the solutions may represent an initial anisotropic stage of our Universe, that later, due to the expansion, became isotropic.

A Generalization of the Dual Immaculate Quasisymmetric Functions in Partially Commutative Variables

A Generalization of the Dual Immaculate Quasisymmetric Functions in Partially Commutative Variables

Neutron Star in Quantized Space-Time

We construct and analyze a model of a neutron star in a κ-deformed space-time. This is conducted by first deriving the κ-deformed generalization of the Einstein tensor, starting from the non-commutative generalization of the metric tensor. By generalizing the energy-momentum tensor to the non-commutative space-time and exploiting the κ-deformed dispersion relation, we then set up Einstein’s field equations in the κ-deformed space-time. As we adopt a realization of the non-commutative coordinates in terms of the commutative coordinates and their derivatives, our model is constructed in terms of commutative variables. Using this, we derive the κ-deformed generalization of the Tolman–Oppenheimer–Volkoff equation. Now, by treating the interior of the star as a perfect fluid as in the commutative space-time, we investigate the modification of the neutron star’s mass due to the non-commutativity of space-time, valid up to first order in the deformation parameter. We show that the non-commutativity of space-time enhances the mass limit of the neutron star. We show that the radius and maximum mass of the neutron star depend on the deformation parameter. Further, our study shows that the mass increases as the radius increases for fixed values of the deformation parameter. We show that maximum mass and radius increase as the deformation parameter increases. We find that the mass varies from 0.26M⊙ to 3.68M⊙ as the radius changes from 8.45 km to 18.66 km. Using the recent observational limits on the upper bound of the mass of a neutron star, we find the deformation parameter to be |a|∼10−44 m. We also show that the compactness and surface redshift of the neutron star increase with its mass.

On the discrete Heisenberg group and commutative modular variables in quantum mechanics: II. Synchronization of unitary actions and homological Abelianization

On the discrete Heisenberg group and commutative modular variables in quantum mechanics: II. Synchronization of unitary actions and homological Abelianization

On the discrete Heisenberg group and commutative modular variables in quantum mechanics: I. The Abelian symplectic shadow and integrality of area

On the discrete Heisenberg group and commutative modular variables in quantum mechanics: I. The Abelian symplectic shadow and integrality of area

Hopf Algebra Structure of Generalized Quasi-Symmetric Functions in Partially Commutative Variables

We introduce a coloured generalization $\mathrm{NSym}_A$ of the Hopf algebra of non-commutative symmetric functions described as a subalgebra of the of rooted ordered coloured trees Hopf algebra. Its natural basis can be identified with the set of sentences over alphabet $A$ (the set of colours). We present also its graded dual algebra $\mathrm{QSym}_A$ of coloured quasi-symmetric functions together with its realization in terms of power series in partially commutative variables. We provide formulas expressing multiplication, comultiplication and the antipode for these Hopf algebras in various bases — the corresponding generalizations of the complete homogeneous, elementary, ribbon Schur and power sum bases of $\mathrm{NSym}$, and the monomial and fundamental bases of $\mathrm{QSym}$. We study also certain distinguished series of trees in the setting of restricted duals to Hopf algebras.

Varieties of commutative semigroups closed under dominions

In this paper, we find sufficient conditions for some commutative varieties of semigroups to be closed under dominions.

Complete noncommutativity in a cosmological model with radiation

In order to try explaining the present accelerated expansion of the universe, we consider the most complete noncommutativity, of a certain type, in a Friedmann–Robertson–Walker cosmological model, coupled to a perfect fluid. We use the ADM formalism in order to write the gravitational Hamiltonian of the model and the Schutz’s formalism in order to write the perfect fluid Hamiltonian. The noncommutativity is introduced by four nontrivial Poisson brackets between all geometrical as well as matter variables of the model. Each nontrivial Poisson bracket is associated with a noncommutative parameter. We recover the description in terms of commutative variables by introducing four variables transformations that depend on the noncommutative parameters. Using those variables transformations, we rewrite the total noncommutative Hamiltonian of the model in terms of commutative variables. From the resulting Hamiltonian, we obtain the scale factor dynamical equations for a generic perfect fluid. In order to solve these equations, we restrict our attention to a model where the perfect fluid is radiation. The solutions depend on six parameters: the four noncommutative parameters, a parameter associated with the fluid energy C, and the curvature parameter k. They also depend on the initial conditions of the model variables. We compare the noncommutative solutions to the corresponding commutative ones and determine how the former ones differ from the latter ones. The comparison shows that the noncommutative model is very useful for describing the accelerated expansion of the universe. We also obtain estimates for one of the noncommutative parameters.

On a class of automorphisms in H2 which resemble the property of preserving volume

AbstractWe give a possible extension of definition of shears and overshears in the case of two non commutative (quaternionic) variables in relation with the associated vector fields and flows. We define the divergence operator and determine the vector fields with divergence. Given the non‐existence of quaternionic volume form on H2, we define automorphisms with volume to be time‐one maps of vector fields with divergence and volume preserving automorphisms to be time‐one maps of vector fields with divergence 0. To these two classes the Andersen–Lempert theory applies. Finally, we exhibit an example of a quaternionic automorphism, which is not in the closure of the set of finite compositions of volume preserving quaternionic shears even though its restriction to the complex subspace is in the closure of the set of finite compositions of complex shears.

Divergence zero quaternionic vector fields and Hamming graphs

We give a possible extension of the definition of quaternionic power series, partial derivatives and vector fields in the case of two (and then several) non commutative (quaternionic) variables. In this setting we also investigate the problem of describing zero functions which are not null functions in the formal sense. A connection between an analytic condition and a graph theoretic property of a subgraph of a Hamming graph is shown, namely the condition that polynomial vector field has formal divergence zero is equivalent to connectedness of subgraphs of Hamming graphs H ( d , 2) . We prove that monomials in variables z and w are always linearly independent as functions only in bidegrees ( p , 0), ( p , 1), (0, q ), (1, q ) and (2, 2).

Relationships between bounded languages, counter machines, finite-index grammars, ambiguity, and commutative regularity

It is shown that for every language family that is a trio containing only semilinear languages, all bounded languages in it can be accepted by one-way deterministic reversal-bounded multicounter machines (DCM). This implies that for every semilinear trio (where these properties are effective), it is possible to decide containment, equivalence, and disjointness concerning its bounded languages. A condition is also provided for when the bounded languages in a semilinear trio coincide exactly with those accepted by DCM machines, and it is used to show that many grammar systems of finite index — such as finite-index matrix grammars (Mfin) and finite-index ET0L (ET0Lfin) — have identical bounded languages as DCM.Then connections between ambiguity, counting regularity, and commutative regularity are made, as many machines and grammars that are unambiguous can only generate/accept counting regular or commutatively regular languages. Thus, such a system that can generate/accept a non-counting regular or non-commutatively regular language implies the existence of inherently ambiguous languages over that system. In addition, it is shown that every language generated by an unambiguous Mfin has a rational characteristic series in commutative variables, and is counting regular. This result plus the connections are used to demonstrate that the grammar systems Mfin and ET0Lfin can generate inherently ambiguous languages (over their grammars), as do several machine models. It is also shown that all bounded languages generated by these two grammar systems (those in any semilinear trio) can be generated unambiguously within the systems. Finally, conditions on Mfin and ET0Lfin languages implying commutative regularity are obtained. In particular, it is shown that every finite-index ED0L language is commutatively regular.

Internal coalgebras in cocomplete categories: Generalizing the Eilenberg–Watts theorem

The category of internal coalgebras in a cocomplete category [Formula: see text] with respect to a variety [Formula: see text] is equivalent to the category of left adjoint functors from [Formula: see text] to [Formula: see text]. This can be seen best when considering such coalgebras as finite coproduct preserving functors from [Formula: see text], the dual of the Lawvere theory of [Formula: see text], into [Formula: see text]: coalgebras are restrictions of left adjoints and any such left adjoint is the left Kan extension of a coalgebra along the embedding of [Formula: see text] into [Formula: see text]. Since [Formula: see text]-coalgebras in the variety [Formula: see text] for rings [Formula: see text] and [Formula: see text] are nothing but left [Formula: see text]-, right [Formula: see text]-bimodules, the equivalence above generalizes the Eilenberg–Watts theorem and all its previous generalizations. By generalizing and strengthening Bergman’s completeness result for categories of internal coalgebras in varieties, we also prove that the category of coalgebras in a locally presentable category [Formula: see text] is locally presentable and comonadic over [Formula: see text] and, hence, complete in particular. We show, moreover, that Freyd’s canonical constructions of internal coalgebras in a variety define left adjoint functors. Special instances of the respective right adjoints appear in various algebraic contexts and, in the case where [Formula: see text] is a commutative variety, are coreflectors from the category [Formula: see text] into [Formula: see text].

A topological approach to non-uniform complexity

We investigate the feasibility of a topological method for proving separations of non-uniform circuit classes. Thereto, we chose a rather simple class of circuits: non-uniform constant size circuit classes with gate types underlying certain restrictions. In particular, we consider gate types admitting for a description through regular and commutative varieties of languages. Given a variety of regular languages V describing the gate types, we proceed by giving an alternative characterisation of the class of languages recognised by constant size circuits with the respective gates. This alternative description mainly relies on the block product principle (or substitution principle), which we extend to work with non-regular languages. The extended version of the block product principle is then used as the main tool to derive ultrafilter equations for the languages recognised by non-uniform constant size circuits with gates described by V, depending on the profinite equations that define the variety of regular languages V.

On the Varieties of Commutative Metabelian Algebras

The paper presents new results on varieties of commutative metabelian algebras over a field of zero characteristic. We study the structure of the multilinear part of the variety of all commutative metabelian algebras as a module of the symmetric group. Two almost nilpotent varieties are introduced and studied in this class of algebras. We prove the nonexistence of other almost nilpotent commutative metabelian varieties of subexponential growth.

On images of locally finite derivations and [formula omitted]-derivations

Some cases of the LFED Conjecture, proposed by the second author [15], for certain integral domains are proved. In particular, the LFED Conjecture is completely established for the field of fractions k(x) of the polynomial algebra k[x], the formal power series algebra k[[x]] and the Laurent formal power series algebra k[[x]][x−1], where x=(x1,x2,…,xn) denotes n commutative free variables and k a field of characteristic zero. Furthermore, the relation between the LFED Conjecture and the Duistermaat–van der Kallen Theorem [3] is also discussed and emphasized.

Two-particle system in Coulomb potential for twist-deformed space-time

In this article, we define a two-particle system in Coulomb potential for twist-deformed space-time with spatial directions commuting to time-dependent function . Particularly, we provide the proper Hamiltonian function and further, we rewrite it in terms of commutative variables. Besides, we demonstrate, that for small values of deformation parameters, the obtained in the perturbation framework, first-ordered corrections for ground helium energy are equal to zero. In such a way, we show that the nontrivial impact of space-time noncommutativity appears only at the second order of the quantum-mechanical correction expansion.

Special elements of the lattice of monoid varieties

We completely classify all neutral or costandard elements in the lattice $\mathbb{MON}$ of all monoid varieties. Further, we prove that an arbitrary upper-modular element of $\mathbb{MON}$ except the variety of all monoids is either a completely regular or a commutative variety. Finally, we verify that all commutative varieties of monoids are codistributive elements of $\mathbb{MON}$. Thus, the problems of describing codistributive or upper-modular elements of $\mathbb{MON}$ are completely reduced to the completely regular case.

Hopf monoids in varieties

Commutative varieties provide a natural setting for generalizing Hopf algebra theory over commutative rings, since they satisfy the various conditions identified in the category theoretical analysis of this theory to guarantee for example the existence of all naturally occurring forgetful functors in this context, the existence of universal measuring comonoids and the existence of generalized finite duals. It will be shown in addition, that crucial properties of the latter, known from the case of Hopf algebra theory over commutative rings, can be generalized Hopf algebra theory over a commutative variety. The attempt to generalize its construction leads to a couple of questions concerning properties of the monoidal structure of a commutative variety, which seem to be of a more general interest.

Noncommutative cosmological model in the presence of a phantom fluid

We study noncommutative classical Friedmann-Robertson-Walker cosmological models. The constant curvature of the spatial sections can be positive ($k=1$), negative ($k=-1$) or zero ($k=0$). The matter is represented by a perfect fluid with negative pressure, phantom fluid, which satisfies the equation of state $p =\alpha \rho$ , with $\alpha < - 1$, where $p$ is the pressure and $\rho$ is the energy density. We use Schutz's formalism in order to write the perfect fluid Hamiltonian. The noncommutativity is introduced by nontrivial Poisson brackets between few variables of the models. In order to recover a description in terms of commutative variables, we introduce variables transformations that depend on a noncommutative parameter ($\gamma$). The main motivation for the introduction of the noncommutativity is trying to explain the present accelerated expansion of the universe. We obtain the dynamical equations for these models and solve them. The solutions have four constants: $\gamma$, a parameter associated with the fluid energy $C$, $k$, $\alpha$ and the initial conditions of the models variables. For each value of $\alpha$, we obtain different equations of motion. Then, we compare the evolution of the universe between the present noncommutative models and the corresponding commutative ones ($\gamma \to 0$). The results show that $\gamma$ is very useful for describing an accelerating universe. We estimate the value of $\gamma$, for the present conditions of the Universe. Then, using that value of $\gamma$, in one of the noncommutative cosmological models, we compute the amount of time this universe would take to reach the {\it big rip}.