6,765 research outputs found
Biofueling rural development: making the case for linking biofuel production to rural revitalization
Biofuels play a crucial role in America\u27s quest for oil independence. In recent years, the biofuel industry has seen significant technology and efficiency advances, as well as expansions in the materials that can be used to create biofuels. Grains and oilseeds are limited in their ability to meet fuel needs, but a shift to biomass feedstocks offers better production possibilities. For rural communities, locally owned biomass refineries may offer promise of new investment, job growth, and revitalization
Unifying R-symmetry in M-theory
In this contribution we address the following question: Is there a group with
a fermionic presentation which unifies all the physical gravitini and dilatini
of the maximal supergravity theories in D=10 and D=11 (without introducing new
degrees of freedom)? The affirmative answer relies on a new mathematical object
derived from the theory of Kac--Moody algebras, notably E10. It can also be
shown that in this way not only the spectrum but also dynamical aspects of all
supergravity theories can be treated uniformly.Comment: 17 pages. Proceedings of ICMP 200
IIA and IIB spinors from K(E10)
We analyze the decomposition of recently constructed unfaithful spinor
representations of K(E10) under its SO(9) x SO(9), and SO(9) x SO(2) subgroups,
respectively, where K(E10) is the `maximal compact' subgroup of the hyperbolic
Kac--Moody group E(10). We show that under these decompositions, respectively,
one and the same K(E10) spinor gives rise to both the fermionic fields of IIA
supergravity, and to the (chiral) fermionic fields of IIB supergravity. This
result is thus the fermionic analogue of the decomposition of E(10) under its
SO(9,9) and SL(9) x SL(2) subgroups, respectively, which yield the correct
bosonic multiplets of (massive) IIA and IIB supergravity. The essentially
unique Lagrangian for the supersymmetric E(10)/K(E10) sigma-model therefore can
also capture the dynamics of IIA and IIB including bosons and fermions in the
known truncations.Comment: 16 pages, v2: added paragraph on spinors for K(E9) and K(E11
Recognising a partitionable simplicial complex is in NP
We show that the problem of recognising a partitionable simplicial complex is a member of the complexity class NP, thus answering a question raised in [1
IIB supergravity and E10
We analyse the geodesic E10/K(E10) sigma-model in a level decomposition
w.r.t. the A8xA1 subalgebra of E10, adapted to the bosonic sector of type IIB
supergravity, whose SL(2,R) symmetry is identified with the A1 factor. The
bosonic supergravity equations of motion, when restricted to zeroth and first
order spatial gradients, are shown to match with the sigma-model equations of
motion up to level four. Remarkably, the self-duality of the five-form field
strength is implied by E10 and the matching.Comment: 14 page
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
Loops in exceptional field theory
We study certain four-graviton amplitudes in exceptional field theory in
dimensions up to two loops. As the formulation is manifestly
invariant under the U-duality group , our resulting
expressions can be expressed in terms of automorphic forms. In the low energy
expansion, we find terms in the M-theory effective action of type ,
and with automorphic coefficient functions in
agreement with independent derivations from string theory. This provides in
particular an explicit integral formula for the exact string theory threshold function. We exhibit moreover that the usual supergravity
logarithmic divergences cancel out in the full exceptional field theory
amplitude, within an appropriately defined dimensional regularisation scheme.
We also comment on terms of higher derivative order and the role of the section
constraint for possible counterterms.Comment: 1+78 pages: v2: Added references and typos corrected. Version
accepted by JHEP. v3: corrected discussion of associativity in EFT and other
typo
E10 Cosmology
We construct simple exact solutions to the E10/K(E10) coset model by
exploiting its integrability. Using the known correspondences with the bosonic
sectors of maximal supergravity theories, these exact solutions translate into
exact cosmological solutions. In this way, we are able to recover some recently
discovered solutions of M-theory exhibiting phases of accelerated expansion,
or, equivalently, S-brane solutions, and thereby accommodate such solutions
within the E10/K(E10) model. We also discuss the difficulties regarding
solutions with non-vanishing (constant) curvature of the internal manifold.Comment: 16 pages, 1 figure. v2: Additional reference
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