1,419 research outputs found
Oxidizing Borcherds symmetries
The tensor hierarchy of maximal supergravity in D dimensions is known to be
closely related to a Borcherds (super)algebra that is constructed from the
global symmetry group E(11-D). We here explain how the Borcherds algebras in
different dimensions are embedded into each other and can be constructed from a
unifying Borcherds algebra. The construction also has a natural physical
explanation in terms of oxidation. We then go on to show that the Hodge duality
that is present in the tensor hierarchy has an algebraic counterpart. For D>8
the Borcherds algebras we find differ from the ones existing in the literature
although they generate the same tensor hierarchy.Comment: 21 pages, 3 figures, 5 table
Symmetries of M-theory and free Lie superalgebras
We study systematically various extensions of the Poincar\'e superalgebra.
The most general structure starting from a set of spinorial supercharges
is a free Lie superalgebra that we discuss in detail. We explain how
this universal extension of the Poincar\'e superalgebra gives rise to many
other algebras as quotients, some of which have appeared previously in various
places in the literature. In particular, we show how some quotients can be very
neatly related to Borcherds superalgebras. The ideas put forward also offer
some new angles on exotic branes and extended symmetry structures in M-theory.Comment: 36 pages. v2: References added, JHEP versio
Does High Inflation Cause Central Bankers to Lose their Job? Evidence Based on a New Data Set
This paper introduces new data on the term in office of central bank governors in 137 countries for 1970-2004. Our panel models show that the probability that a central bank governor is replaced in a particular year is positively related to the share of the term in office elapsed, political and regime instability, the occurrence of elections, and inflation. The latter result suggests that the turnover rate of central bank governors (TOR) is a poor indicator of central bank independence. This is confirmed in models for cross-section inflation in which TOR becomes insignificant once its endogeneity is taken into account.central bank governors, central bank independence, inflation
Beyond E11
We study the non-linear realisation of E11 originally proposed by West with
particular emphasis on the issue of linearised gauge invariance. Our analysis
shows even at low levels that the conjectured equations can only be invariant
under local gauge transformations if a certain section condition that has
appeared in a different context in the E11 literature is satisfied. This
section condition also generalises the one known from exceptional field theory.
Even with the section condition, the E11 duality equation for gravity is known
to miss the trace component of the spin connection. We propose an extended
scheme based on an infinite-dimensional Lie superalgebra, called the tensor
hierarchy algebra, that incorporates the section condition and resolves the
above issue. The tensor hierarchy algebra defines a generalised differential
complex, which provides a systematic description of gauge invariance and
Bianchi identities. It furthermore provides an E11 representation for the field
strengths, for which we define a twisted first order self-duality equation
underlying the dynamics.Comment: 97 pages. v2: Minor changes, references added. Published versio
Galilean free Lie algebras
We construct free Lie algebras which, together with the algebra of spatial rotations, form infinite-dimensional extensions of finite-dimensional Galilei Maxwell algebras appearing as global spacetime symmetries of extended non-relativistic objects and non-relativistic gravity theories. We show how various extensions of the ordinary Galilei algebra can be obtained by truncations and contractions, in some cases via an affine Kac-Moody algebra. The infinite-dimensional Lie algebras could be useful in the construction of generalized Newton-Cartan theories gravity theories and the objects that couple to them
Optimal 3D Cell Planning: A Random Matrix Approach
International audienceThis article proposes a large system approximation of the ergodic sum-rate (SR) for cellular multi-user multiple-input multiple-output uplink systems. The considered system has various degrees of freedom, such as clusters of base stations (BSs) performing cooperative multi-point processing, randomly distributed user terminals (UTs), and supports arbitrarily configurable antenna gain patterns at the BSs. The approximation is provably tight in the limiting case of a large number of single antenna UTs and antennas at the BSs. Simulation results suggest that the asymptotic analysis is accurate for small system dimensions. Our deterministic SR approximation result is applied to numerically study and optimize the effects of antenna tilting in an exemplary sectorized 3D small cell network topology. Significant SR gains are observed with optimal tilt angles and we provide new insights on the optimal parameterization of cellular networks, along with a discussion of several non-trivial effects
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