205 research outputs found
New Directions for New Dimensions: From Strings to Neutrinos to Axions to...
In this talk, I discuss recent developments concerning the possibility of
large extra spacetime dimensions. After briefly reviewing how such dimensions
can lower the fundamental GUT, Planck, and string scales, I then outline how
these scenarios lead to a new higher-dimensional seesaw mechanism for
generating neutrino oscillations --- perhaps even without neutrino masses. I
also discuss how extra dimensions lead to new mechanisms contributing to the
``invisibility'' of the QCD axion. This talk reports on work done in
collaboration with Emilian Dudas and Tony Gherghetta.Comment: 12 pages, LaTeX, 4 figures. Invited plenary talk given at PASCOS '99
(held at Lake Tahoe, California, 10-16 December 1999). To appear in the
Proceeding
SPACETIME PROPERTIES OF (1,0) STRING VACUA
We discuss one of the generic spacetime consequences of having (1,0)
worldsheet supersymmetry in tachyon-free string theory, namely the appearance
of a ``misaligned supersymmetry'' in the corresponding spacetime spectrum.
Misaligned supersymmetry is a universal property of (1,0) string vacua which
describes how the arrangement of bosonic and fermionic states at all string
energy levels conspires to preserve finite string amplitudes, even in the
absence of full spacetime supersymmetry. Misaligned supersymmetry also
constrains the degree to which spacetime supersymmetry can be broken without
breaking modular invariance, and is responsible for the vanishing of various
mass supertraces evaluated over the infinite string spectrum.
[Talk delivered at Strings '95, based on material drawn from hep-th/9402006
and hep-th/9409114. To appear in Proceedings.]Comment: 6 pages, LaTeX, one encapsulated figur
How Strings Make Do without Supersymmetry: An Introduction to Misaligned Supersymmetry
We provide a non-technical introduction to "misaligned supersymmetry", a
generic phenomenon in string theory which describes how the arrangement of
bosonic and fermionic states at all string energy levels conspires to preserve
finite string amplitudes even in the absence of spacetime supersymmetry.
Misaligned supersymmetry thus naturally constrains the degree to which
spacetime supersymmetry can be broken in string theory while preserving the
finiteness of string amplitudes, and explains how the requirements of modular
invariance and absence of physical tachyons affect the distribution of states
throughout the string spectrum.Comment: 13 pages, uuencoded PostScript (with figures already embedded) [Talk
presented at MRST '94: "What Next? Exploring the Future of High-Energy
Physics" (held at McGill University, Montreal, Canada, 11--13 May 1994), and
at PASCOS '94: "Particles, Strings, and Cosmology" (held at Syracuse
University, Syracuse, NY, 19--24 May 1994). To appear in Proceedings
published by World Scientific.
Shape versus Volume: Making Large Flat Extra Dimensions Invisible
Much recent attention has focused on theories with large extra compactified
dimensions. However, while the phenomenological implications of the volume
moduli associated with such compactifications are well understood, relatively
little attention has been devoted to the shape moduli. In this paper, we show
that the shape moduli have a dramatic effect on the corresponding Kaluza-Klein
spectra: they change the mass gap, induce level crossings, and can even be used
to interpolate between theories with different numbers of compactified
dimensions. Furthermore, we show that in certain cases it is possible to
maintain the ratio between the higher-dimensional and four-dimensional Planck
scales while simultaneously increasing the Kaluza-Klein graviton mass gap by an
arbitrarily large factor. This mechanism can therefore be used to alleviate (or
perhaps even eliminate) many of the experimental bounds on theories with large
extra spacetime dimensions.Comment: 9 pages, LaTeX, 5 figure
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