65,496 research outputs found
The low energy expansion of the one-loop type II superstring amplitude
The one-loop four-graviton amplitude in either of the type II superstring
theories is expanded in powers of the external momenta up to and including
terms of order s^4 log s R^4, where R^4 denotes a specific contraction of four
linearized Weyl tensors and s is a Mandelstam invariant. Terms in this series
are obtained by integrating powers of the two-dimensional scalar field theory
propagator over the toroidal world-sheet as well as the moduli of the torus.
The values of these coefficients match expectations based on duality relations
between string theory and eleven-dimensional supergravity.Comment: harvmac (b), 25 pages, 3 eps figures. v2: Factors of 2 corrected.
Conclusion unchange
Gauge symmetries decrease the number of Dp-brane dimensions
It is known that the presence of antisymmetric background field
leads to noncommutativity of Dp-brane manifold. Addition of the linear dilaton
field in the form , causes the appearance of the
commutative Dp-brane coordinate . In the present article we show
that for some particular choices of the background fields, and $\tilde a^2\equiv [ (G-4BG^{-1}B)^{-1}\
]^{\mu\nu}a_\mu a_\nu=0$, the local gauge symmetries appear in the theory. They
turn some Neuman boundary conditions into the Dirichlet ones, and consequently
decrease the number of the Dp-brane dimensions.Comment: We improve Sec.4. and Conclusion and we added the Appendix in order
to clarify result
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From bedside to bench: Comroe and dripps revisited
Twenty-five years ago a paper published in Science by Julius Comroe and Robert Dripps purported to demonstrate that 41 per cent of all articles judged to be essential for later clinical advances were not clinically oriented at the time of the study and 62 per cent of key articles were the result of basic research.
Since that analysis, support for basic research has increased in the G7 countries. In the UK, Research Council expenditure on basic research has increased from a low of ÂŁ444 million (or 42 per cent of total civil R&D) in 1991/92 to ÂŁ769 million (or 61 per cent of total civil R&D) in 1998/99. Although it would be difficult to argue that Comroe and Dripps were directly responsible for a strategic shift (or drift) in the type of science supported by research funders, their arguments are often cited (albeit at times implicitly) in support of the increased funding for basic biomedical research.
In 1987 Richard Smith wrote a critical paper reassessing Comroe and Dripps. His main argument was that the original study was in itself âunscientificâ and that it should be âfollowed by bigger and better studiesâ. This study is, in part, an answer to that challenge.
Given the increased support for basic research, and the apparent importance based on the work of Comroe and Dripps, we felt it was important to investigate Smithâs comments by replicating Comroe and Drippsâs study and at the same time try to improve upon the methodology. The current project had two objectives:
1. To see if the original Comroe and Drippsâs methodology was âreplicableâ.
2. To validate the key findings of Comroe and Dripps.
By looking at neonatal intensive care (NIC), we concluded that Comroe and Drippsâ study â as reported â is not repeatable, reliable or valid, and thus is an insufficient evidence base for increased expenditure on basic biomedical research. We did, however, develop an alternative methodology which used bibliographic databases and bibliometric techniques to describe the research underpinning five of the most important clinical advances in NIC, as identified through a Delphi survey.
Using the revised bibliometric protocol, we demonstrated that after a time-lag of about 17 years, between 2 and 21 per cent of research underpinning the clinical advances could be described as basic. This observation is at odds with Comroe and Drippsâs finding that 62 per cent of key research articles judged to be essential for latter clinical advance were the result of basic research.
In reaching this conclusion we are acutely aware of the significant limitations to the revised methodology and, therefore, we caution against the over-interpretation of our results. However, we would argue that there needs to be a greater understanding of how basic research supports healthcare and hope this report will inform part of this wider debate.R&D Directorate of the NHS Executive London; Wellcome Trus
String Bit Models for Superstring
We extend the model of string as a polymer of string bits to the case of
superstring. We mainly concentrate on type II-B superstring, with some
discussion of the obstacles presented by not II-B superstring, together with
possible strategies for surmounting them. As with previous work on bosonic
string we work within the light-cone gauge. The bit model possesses a good deal
less symmetry than the continuous string theory. For one thing, the bit model
is formulated as a Galilei invariant theory in dimensional
space-time. This means that Poincar\'e invariance is reduced to the Galilei
subgroup in space dimensions. Naturally the supersymmetry present in the
bit model is likewise dramatically reduced. Continuous string can arise in the
bit models with the formation of infinitely long polymers of string bits. Under
the right circumstances (at the critical dimension) these polymers can behave
as string moving in dimensional space-time enjoying the full
Poincar\'e supersymmetric dynamics of type II-B superstring.Comment: 43 pages, phyzzx require
Supersymmetry Constraints on Type IIB Supergravity
Supersymmetry is used to derive conditions on higher derivative terms in the
effective action of type IIB supergravity. Using these conditions, we are able
to prove earlier conjectures that certain modular invariant interactions of
order alpha' **3 relative to the Einstein-Hilbert term are proportional to
eigenfunctions of the Laplace operator on the fundamental domain of SL(2,Z). We
also discuss how these arguments generalize to terms of higher order in alpha',
as well as to compactifications of supergravity.Comment: 31 pages, harvmac (b); minor correction
Teacher Leader Administrators: Part 3 Of A Symposium On Teachers As Leaders
In this latest continuation of our multipart symposium on teacher leadership, we examine what happens when self-defined teacher leaders become school administrators. Do teacher leaders who become administrators maintain a teacher identity? Can they remain committed to their vision of teacher leadership when they take on the normative requirements and responsibilities of school administration? Through a conversation with three teachers leaders, we explore the rewards and trials of teaching, the choice to become teacher leaders and then administrators, and the unique challenges that face administrators who deeply value the professional, political, and collaborative work of teachers
Remarks on the Classical Size of D-Branes
We discuss different criteria for `classical size' of extremal Dirichlet
p-branes in type-II supergravity. Using strong-weak coupling duality, we find
that the size of the strong-coupling region at the core of the (p<3)-branes, is
always given by the asymptotic string scale, if measured in the weakly coupled
dual string metric. We also point out how the eleven-dimensional Planck scale
arises in the classical 0-brane solution, as well as the ten-dimensional Planck
scale in the D-instanton solution.Comment: 8 pp, harvma
Galois covers of the open p-adic disc
This paper investigates Galois branched covers of the open -adic disc and
their reductions to characteristic . Using the field of norms functor of
Fontaine and Wintenberger, we show that the special fiber of a Galois cover is
determined by arithmetic and geometric properties of the generic fiber and its
characteristic zero specializations. As applications, we derive a criterion for
good reduction in the abelian case, and give an arithmetic reformulation of the
local Oort Conjecture concerning the liftability of cyclic covers of germs of
curves.Comment: 19 pages; substantial organizational and expository changes; this is
the final version corresponding to the official publication in Manuscripta
Mathematica; abstract update
Combinatorics of Boundaries in String Theory
We investigate the possibility that stringy nonperturbative effects appear as
holes in the world-sheet. We focus on the case of Dirichlet string theory,
which we argue should be formulated differently than in previous work, and we
find that the effects of boundaries are naturally weighted by .Comment: 12 pages, 2 figures, LaTe
Mass corrections in string theory and lattice field theory
Kaluza-Klein compactifications of higher dimensional Yang-Mills theories
contain a number of four dimensional scalars corresponding to the internal
components of the gauge field. While at tree-level the scalar zero modes are
massless, it is well known that quantum corrections make them massive. We
compute these radiative corrections at 1-loop in an effective field theory
framework, using the background field method and proper Schwinger-time
regularization. In order to clarify the proper treatment of the sum over
KK--modes in the effective field theory approach, we consider the same problem
in two different UV completions of Yang-Mills: string theory and lattice field
theory. In both cases, when the compactification radius is much bigger than
the scale of the UV completion (), we recover a mass
renormalization that is independent of the UV scale and agrees with the one
derived in the effective field theory approach. These results support the idea
that the value of the mass corrections is, in this regime, universal for any UV
completion that respects locality and gauge invariance. The string analysis
suggests that this property holds also at higher loops. The lattice analysis
suggests that the mass of the adjoint scalars appearing in
Super Yang-Mills is highly suppressed due to an interplay between the
higher-dimensional gauge invariance and the degeneracy of bosonic and fermionic
degrees of freedom.Comment: 27 page
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