23 research outputs found
From noncommutative string/membrane to ordinary ones
We discuss origin of equivalence between noncommutative and ordinary
Yang-Mills from point of view of string theory. Working in BRST/Hamiltonian
framework first we investigate string model in the decoupling limit and show
that change of variables and applying the conversion of constraints of
decoupled string theory gives commuting coordinates on the D-brane. Also, we
discuss algebra of constraints in general case and show the ways of having
commutative coordinates without going to decoupling limit. It could be argued
that noncommutative string in B-field is equivalent to the commutative model.
We investigate the case of the membrane ending on the M-5-brane in constant
C-field and discuss noncommutative/commutative equivalence in this case.Comment: 15 pages, Latex. Comments added and typos correcte
Superparticles in D>11
Actions for two-superparticle system in (10,2) dimensions and
three-superparticle systems in (11,3) dimensions are constructed. These actions
have worldline bosonic and fermionic local symmetries, and target space global
supersymmety generalizing the reparametrization, kappa-symmetry and Poincare
supersymmetry of the usual superparticle. With the second particle, or the
second and third particles on-shell, they describe a superparticle propagating
in the background of a second superparticle in (10,2) dimensions, or two other
superparticles in (11,3) dimensions. Symmetries of the action are shown to
exist in presence of super Yang-Mills background as well.Comment: 12 pages, latex, replaced Note Added to appear as an Addendu
BREMSSTRAHLUNG FORMATION IN THE DUAL ENERGY METHOD FOR RADIOGRAPHY OF THE UNAUTHORIZED EMBEDDING
The possibility of an effective method of dual-energy radiography unauthorized inclusions containing heavy elements in cargo containers has been investigated. A method for optimizing the energy performance of the bremsstrahlung radiation: low-energy beam (containing the maximum number of photons in the energy range, which is dominated by Compton effect) and high energy beam (with a maximum number of high-energy photons, electron-positron pairs) has been developed. The influence of the converter thickness and converter material on the spectral characteristics of the beams of photons has been investigated. The variants of treelayers efficient converters have been proposed. On the basis of the Monte Carlo and quasi-analytical method a numerical experiment radiography investments has been completed. It is shown that the use of optimally shaped beams can reliably distinguish embedding
from lead to masking the background of steel structures up to 25 c
Superparticles, p-form coordinates and the BPS condition
A model for superparticles in dimensions is studied. The target
space supersymmetry involves a product of momentum generators, and the
action has local bosonic symmetries and local fermionic
symmetries. The precise relation between the symmetries presented here and
those existing in the literature is explained. A new model is proposed for
superparticles in arbitrary dimensions where coordinates are associated with
all the -form charges occuring in the superalgebra. The model naturally
gives rise to the BPS condition for the charges.Comment: 14 pages, latex, expanded introduction, added references,
restructured sections and changed titl
On zero modes of the eleven dimensional superstring
It is shown that recently pointed out by Berkovits on-shell degrees of
freedom of the D=11 superstring do not make contributions into the quantum
states spectrum of the theory. As a consequence, the spectrum coincides with
that of the D=10 type IIA superstring.Comment: 7 pages, LaTex fil
L-branes
The superembedding approach to -branes is used to study a class of
-branes which have linear multiplets on the worldvolume. We refer to these
branes as L-branes. Although linear multiplets are related to scalar multiplets
(with 4 or 8 supersymmetries) by dualising one of the scalars of the latter to
a -form field strength, in many geometrical situations it is the linear
multiplet version which arises naturally. Furthermore, in the case of 8
supersymmetries, the linear multiplet is off-shell in contrast to the scalar
multiplet. The dynamics of the L-branes are obtained by using a systematic
procedure for constructing the Green-Schwarz action from the superembedding
formalism. This action has a Dirac-Born-Infeld type structure for the -form.
In addition, a set of equations of motion is postulated directly in superspace,
and is shown to agree with the Green-Schwarz equations of motion.Comment: revised version, minor changes, references added, 22 pages, no
figures, LaTe
Two-Time Physics with gravitational and gauge field backgrounds
It is shown that all possible gravitational, gauge and other interactions
experienced by particles in ordinary d-dimensions (one-time) can be described
in the language of two-time physics in a spacetime with d+2 dimensions. This is
obtained by generalizing the worldline formulation of two-time physics by
including background fields. A given two-time model, with a fixed set of
background fields, can be gauged fixed from d+2 dimensions to (d-1) +1
dimensions to produce diverse one-time dynamical models, all of which are
dually related to each other under the underlying gauge symmetry of the unified
two-time theory. To satisfy the gauge symmetry of the two-time theory the
background fields must obey certain coupled differential equations that are
generally covariant and gauge invariant in the target d+2 dimensional
spacetime. The gravitational background obeys a null homothety condition while
the gauge field obeys a differential equation that generalizes a similar
equation derived by Dirac in 1936. Explicit solutions to these coupled
equations show that the usual gravitational, gauge, and other interactions in d
dimensions may be viewed as embedded in the higher d+2 dimensional space, thus
displaying higher spacetime symmetries that otherwise remain hidden.Comment: Latex, 19 pages, references adde
Hermitian versus holomorphic complex and quaternionic generalized supersymmetries of the M-theory. A classification
Relying upon the division-algebra classification of Clifford algebras and
spinors, a classification of generalized supersymmetries (or, with a slight
abuse of language,"generalized supertranslations") is provided. In each given
space-time the maximal, saturated, generalized supersymmetry, compatible with
the division-algebra constraint that can be consistently imposed on spinors and
on superalgebra generators, is furnished. Constraining the superalgebra
generators in both the complex and the quaternionic cases gives rise to the two
classes of constrained hermitian and holomorphic generalized supersymmetries.
In the complex case these two classes of generalized supersymmetries can be
regarded as complementary. The quaternionic holomorphic supersymmetry only
exists in certain space-time dimensions and can admit at most a single bosonic
scalar central charge.
The results here presented pave the way for a better understanding of the
various algebra-type of structures which can be introduced in different
space-time signatures and in association with different division algebras, as
well as their mutual relations. In a previous work, e.g., the introduction of a
complex holomorphic generalized supersymmetry was shown to be necessary in
order to perform the analytic continuation of the standard -theory to the
11-dimensional Euclidean space. As an application of the present results, it is
shown that the above algebra also admits a 12-dimensional, Euclidean,
-algebra presentation.Comment: 25 pages, LaTe
Noncommutative Sp(2,R) Gauge Theories - A Field Theory Approach to Two-Time Physics
Phase-space and its relativistic extension is a natural space for realizing
Sp(2,R) symmetry through canonical transformations. On a Dx2 dimensional
covariant phase-space, we formulate noncommutative field theories, where
Sp(2,R) plays a role as either a global or a gauge symmetry group. In both
cases these field theories have potential applications, including certain
aspects of string theories, M-theory, as well as quantum field theories. If
interpreted as living in lower dimensions, these theories realize Poincare'
symmetry linearly in a way consistent with causality and unitarity. In case
Sp(2,R) is a gauge symmetry, we show that the spacetime signature is determined
dynamically as (D-2,2). The resulting noncommutative Sp(2,R) gauge theory is
proposed as a field theoretical formulation of two-time physics: classical
field dynamics contains all known results of `two-time physics', including the
reduction of physical spacetime from D to (D-2) dimensions, with the associated
`holography' and `duality' properties. In particular, we show that the solution
space of classical noncommutative field equations put all massless scalar,
gauge, gravitational, and higher-spin fields in (D-2) dimensions on
equal-footing, reminiscent of string excitations at zero and infinite tension
limits.Comment: 32 pages, LaTe