8,353 research outputs found
Partially-massless higher-spin algebras and their finite-dimensional truncations
The global symmetry algebras of partially-massless (PM) higher-spin (HS)
fields in (A)dS are studied. The algebras involving PM generators up to
depth are defined as the maximal symmetries of free conformal
scalar field with order wave equation in dimensions. We review
the construction of these algebras by quotienting certain ideals in the
universal enveloping algebra of isometries. We discuss another
description in terms of Howe duality and derive the formula for computing trace
in these algebras. This enables us to explicitly calculate the bilinear form
for this one-parameter family of algebras. In particular, the bilinear form
shows the appearance of additional ideal for any non-negative integer values of
, which coincides with the annihilator of the one-row -box
Young diagram representation of . Hence, the
corresponding finite-dimensional coset algebra spanned by massless and PM
generators is equivalent to the symmetries of this representation.Comment: 22 pages, references added, revised version, accepted to JHE
A note on higher-derivative actions for free higher-spin fields
Higher-derivative theories of free higher-spin fields are investigated
focusing on their symmetries. Generalizing familiar two-derivative constrained
formulations, we first construct less-constrained Einstein-like and
Maxwell-like higher-derivative actions. Then, we construct Weyl-like actions -
the actions admitting constrained Weyl symmetries - with different numbers of
derivatives. They are presented in a factorized form making use of
Einstein-like and Maxwell-like tensors. The last (highest-derivative) member of
the hierarchy of the Weyl-like actions coincides with the Fradkin-Tseytlin
conformal higher-spin action in four dimensions.Comment: Version to appear in JHEP, 22 page
Weyl Action of Two-Column Mixed-Symmetry Field and Its Factorization Around (A)dS Space
We investigate the four-derivative free Weyl action for two-column
mixed-symmetry field that makes use of maximal gauge symmetries. In flat space,
the action can be uniquely determined from gauge and Weyl (trace shift)
symmetry requirements. We show that there is a smooth and unique deformation of
the flat action to (A)dS which keeps the same amount of gauge symmetries. This
action admits a factorization into two distinct two-derivative actions having
gauge parameters of different Young diagrams. Hence, this factorization pattern
naturally extends that of the Weyl actions of symmetric higher spin fields to
mixed-symmetry cases. The mass-deformation for these actions can be realized
preserving one of the gauge symmetries. Although generically non-unitary, in
special dimensions, unitarity is achieved selecting different mass deformations
for dS and AdS. We consider particular examples of our construction such as New
Massive Gravity in three dimensions, linearized bigravity in four dimensions
and their arbitrary dimensional generalizations.Comment: 25 pages, minor corrections, references added, version published in
JHE
Notes on higher-spin algebras: minimal representations and structure constants
The higher-spin (HS) algebras so far known can be interpreted as the
symmetries of the minimal representation of the isometry algebra. After
discussing this connection briefly, we generalize this concept to any classical
Lie algebras and consider the corresponding HS algebras. For sp(2N) and so(N),
the minimal representations are unique so we get unique HS algebras. For sl(N),
the minimal representation has one-parameter family, so does the corresponding
HS algebra. The so(N) HS algebra is what underlies the Vasiliev theory while
the sl(2) one coincides with the 3D HS algebra hs[lambda]. Finally, we derive
the explicit expression of the structure constant of these algebras --- more
precisely, their bilinear and trilinear forms. Several consistency checks are
carried out for our results.Comment: minor corrections, references adde
Higher-derivative massive actions from dimensional reduction
A procedure to obtain higher-derivative free massive actions is proposed. It
consists in dimensional reduction of conventional two-derivative massless
actions, where solutions to constraints bring in higher derivatives. We apply
this procedure to derive the arbitrary dimensional generalizations of
(linearized) New Massive Gravity and New Topologically Massive Gravity.Comment: 18 page
THE EFFECTS OF COMPETITION ON U.S. WHEAT MARKET SHARES IN EAST ASIA
The effects of competition between wheat export countries on the U.S. wheat market shares in ten Asian countries are analyzed. The variables are relative forms of the U.S. against Australian and Canadian variables to incorporate the effects of competition among exporters. From the estimation results, we could not find distinct effects of wheat prices, exchange rates, changes of the prices and currency values, and the U.S. export enhancement program on the U.S. wheat export performance. This implies that further studies are needed to analyze other factors beyond these variables for the Asian wheat import market, such as different protein or type of wheat, importing countries¡¯ trading policies, or utilization of the state trading agencies.International Wheat Trade, Market Share, Panel Estimation, Panel Unit-Root Test
Efros-Shklovskii variable range hopping in reduced graphene oxide sheets of varying carbon sp2 fraction
We investigate the low temperature electron transport properties of
chemically reduced graphene oxide (RGO) sheets with different carbon sp2
fractions of 55 to 80 %. We show that in the low bias (Ohmic) regime, the
temperature (T) dependent resistance (R) of all the devices follow
Efros-Shklovskii variable range hopping (ES-VRH) R ~ exp[(T(ES)/T)^1/2] with
T(ES) decreasing from 30976 to 4225 K and electron localization length
increasing from 0.46 to 3.21 nm with increasing sp2 fraction. From our data, we
predict that for the temperature range used in our study, Mott-VRH may not be
observed even at 100 % sp2 fraction samples due to residual topological defects
and structural disorders. From the localization length, we calculate a bandgap
variation of our RGO from 1.43 to 0.21 eV with increasing sp2 fraction from 55
to 80 % which agrees remarkably well with theoretical prediction. We also show
that, in the high bias regime, the hopping is field driven and the data follow
R ~ exp[(E(0)/E)^1/2] providing further evidence of ES-VRH.Comment: 13 pages, 6 figures, 1 tabl
Looking for partially-massless gravity
We study the possibility for a unitary theory of partially-massless (PM)
spin-two field interacting with Gravity in arbitrary dimensions. We show that
the gauge and parity invariant interaction of PM spin two particles requires
the inclusion of specific massive spin-two fields and leads to a reconstruction
of Conformal Gravity, or multiple copies of the latter in even dimensions. By
relaxing the parity invariance, we find a possibility of a unitary theory in
four dimensions, but this theory cannot be constructed in the standard
formulation, due to the absence of the parity-odd cubic vertex therein.
Finally, by relaxing the general covariance, we show that a `non-geometric'
coupling between massless and PM spin-two fields may lead to an alternative
possibility of a unitary theory. We also clarify some aspects of interactions
between massless, partially-massless and massive fields, and resolve
disagreements in the literature.Comment: 47 pages, journal version with minor correction
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