80 research outputs found
Fermionic T-duality in fermionic double space
In this article we offer the interpretation of the fermionic T-duality of the
type II superstring theory in double space. We generalize the idea of double
space doubling the fermionic sector of the superspace. In such doubled space
fermionic T-duality is represented as permutation of the fermionic coordinates
and with the corresponding fermionic T-dual
ones, and , respectively. Demanding
that T-dual transformation law has the same form as inital one, we obtain the
known form of the fermionic T-dual NS-R i R-R background fields. Fermionic
T-dual NS-NS background fields are obtained under some assumptions. We conclude
that only symmetric part of R-R field strength and symmetric part of its
fermionic T-dual contribute to the fermionic T-duality transformation of
dilaton field and analyze the dilaton field in fermionic double space. As a
model we use the ghost free action of type II superstring in pure spinor
formulation in approximation of constant background fields up to the quadratic
terms.Comment: Four paragraphs in the Introduction added in order to better motivate
the subject, explained the choice of action (detailed derivation
Canonical approach to the closed string noncommutativity
We consider the closed string moving in the weakly curved background and its
totally T-dualized background. Using T-duality transformation laws, we find the
structure of the Poisson brackets in the T-dual space corresponding to the
fundamental Poisson brackets in the original theory. From this structure we
obtain that the commutative original theory is equivalent to the
non-commutative T-dual theory, whose Poisson brackets are proportional to the
background fluxes times winding and momenta numbers. The non-commutative theory
of the present article is more nongeometrical then T-folds and in the case of
three space-time dimensions corresponds to the nongeometric space-time with
-flux.Comment: We add the Sec. 4. where we compared our results with previous ones.
We also improved Abstract, Introduction and Conclusion as described above. In
addition, we corrected all typos and grammatical errors we notice
Atmospheric dispersion and the implications for phase calibration
The success of any ALMA phase-calibration strategy, which incorporates phase
transfer, depends on a good understanding of how the atmospheric path delay
changes with frequency (e.g. Holdaway & Pardo 2001). We explore how the wet
dispersive path delay varies for realistic atmospheric conditions at the ALMA
site using the ATM transmission code. We find the wet dispersive path delay
becomes a significant fraction (>5 per cent) of the non-dispersive delay for
the high-frequency ALMA bands (>160 GHz, Bands 5 to 10). Additionally, the
variation in dispersive path delay across ALMA's 4-GHz contiguous bandwidth is
not significant except in Bands 9 and 10. The ratio of dispersive path delay to
total column of water vapour does not vary significantly for typical amounts of
water vapour, water vapour scale heights and ground pressures above Chajnantor.
However, the temperature profile and particularly the ground-level temperature
are more important. Given the likely constraints from ALMA's ancillary
calibration devices, the uncertainty on the dispersive-path scaling will be
around 2 per cent in the worst case and should contribute about 1 per cent
overall to the wet path fluctuations at the highest frequencies.Comment: 13 pages, 10 figures, ALMA Memo 59
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