29,876 research outputs found
RG-flows and Open/Closed String Duality
We discuss the interpaly between IR and UV divergences in theories with open
and unoriented strings in view of the AdS/CFT correspondence. We start by
deriving general formulas for the computation of threshold corrections to gauge
couplings in generic configurations with open and unoriented strings. These
allow us to discuss the IR/UV correspondence between beta-function coefficients
and ``dilaton'' tadpoles for several brane configurations probed by D3-branes.
Finally we comment on the AdS supergravity descriptions of gauge theories that
are (super)conformal in the large N limit.Comment: Minor corrections. References added. Version to be published in
JHEP08(2000)035. 22 pages, Late
Anomalies & Tadpoles
We show that massless RR tadpoles in vacuum configurations with open and
unoriented strings are always related to anomalies. RR tadpoles arising from
sectors of the internal SCFT with non-vanishing Witten index are in one-to-one
correspondence with conventional irreducible anomalies. The anomalous content
of the remaining RR tadpoles can be disclosed by considering anomalous
amplitudes with higher numbers of external legs. We then provide an explicit
parametrization of the anomaly polynomial in terms of the boundary reflection
coefficients, i.e. one-point functions of massless RR fields on the disk. After
factorization of the reducible anomaly, we extract the relevant WZ couplings in
the effective lagrangians.Comment: 20 pages, Late
Novel calibrations of virial black hole mass estimators in active galaxies based on X-ray luminosity and optical/NIR emission lines
Accurately weigh the masses of SMBH in AGN is currently possible for only a
small group of local and bright broad-line AGN through reverberation mapping
(RM). Statistical demographic studies can be carried out considering the
empirical scaling relation between the size of the BLR and the AGN optical
continuum luminosity. However, there are still biases against low-luminosity or
reddened AGN, in which the rest-frame optical radiation can be severely
absorbed/diluted by the host and the BLR emission lines could be hard to
detect. Our purpose is to widen the applicability of virial-based SE relations
to reliably measure the BH masses also for low-luminosity or intermediate/type
2 AGN that are missed by current methodology. We achieve this goal by
calibrating virial relations based on unbiased quantities: the hard X-ray
luminosities, in the 2-10 keV and 14-195 keV bands, that are less sensitive to
galaxy contamination, and the FWHM of the most important rest-frame NIR and
optical BLR emission lines. We built a sample of RM AGN having both X-ray
luminosity and broad optical/NIR FWHM measurements available in order to
calibrate new virial BH mass estimators. We found that the FWHM of the
H, H and NIR lines (i.e. Pa, Pa and
HeI10830) all correlate each other having negligible or small offsets.
This result allowed us to derive virial BH mass estimators based on either the
2-10 keV or 14-195 keV luminosity. We took also into account the recent
determination of the different virial coefficients for pseudo and classical
bulges. By splitting the sample according to the bulge type and adopting
separate factors we found that our virial relations predict BH masses of
AGN hosted in pseudobulges 0.5 dex smaller than in classical bulges.
Assuming the same average factor for both populations, a difference of
0.2 dex is still found.Comment: 11 pages, 2 figures, 4 tables, accepted for publication on A&
Probing Fuzzballs with Particles, Waves and Strings
We probe D1D5 micro-state geometries with massless particles, waves and
strings. To this end, we study geodetic motion, Klein-Gordon equation and
string scattering in the resulting gravitational background. Due to the reduced
rotational symmetry, even in the simple case of a circular fuzzball, the system
cannot be integrated elementarily. Yet, for motion in the plane of the string
profile or in the orthogonal plane to it, one can compute the deflection angle
or the phase shift and identify the critical impact parameter, at which even a
massless probe is captured by the fuzzball if its internal momentum is properly
tuned. We find agreement among the three approaches, thus giving further
support to the fuzzball proposal at the dynamical level.Comment: 35 pages. Extended and improved discussions on the integrability of
the geodetic equations and on the critical impact parameter
Utilising intrinsic robustness in agricultural production systems: Inventions for a sustainable development of agriculture
This paper explores the potential of utilising robust crops and livestock for improving sustainability of agriculture. Two approaches for dealing with unwanted fluctuations that may influence agricultural production, such as diseases and pests, are discussed. The prevailing approach, which we call the âControl Modelâ, is to protect crops and livestock from disturbances as much as possible, to regain balance with monitoring and intervention and to look for add-on solutions only. There are a number of problems associated with the Control Model, including reduced animal welfare, environmental pollution and low public support. An alternative approach, which we call the âAdaptation Modelâ, is based on reducing the consequences of disturbances rather than taking disturbances ou
On stringy AdS_5 x S^5 and higher spin holography
We derive the spectrum of Kaluza-Klein descendants of string excitations on
AdS_5 x S^5. String states are organized in long multiplets of the AdS
supergroup SU(2,2|4,R) with a rich pattern of shortenings at the higher spin
enhancement point \lambda=0. The string states holographically dual to the
higher spin currents of SYM theory in the strict zero coupling limit are
identified together with the corresponding Goldstone particles responsible for
the Higgsing of the higher spin symmetry at \lambda\neq 0. Exploiting higher
spin symmetry we propose a very simple yet effective mass formula and establish
a one-to-one correspondence between the complete spectrum of \Delta_0 <= 4
string states and relevant/marginal single-trace deformations in N=4 SYM theory
at large N. To this end, we describe how to efficiently enumerate scaling
operators in `free' YM theory, with the inclusion of fermionic `letters', by
resorting to Polya theory. Comparison between the spectra of 1/4-BPS states is
also presented. Finally, we discuss how to organize the spectrum of N=4 SYM
theory in SU(2,2|4,R) supermultiplets by means of some kind of `Eratostenes's
sieve'.Comment: 38 pages, LateX2e, references adde
The role of magnetic field for quiescence-outburst models in CVs
In this paper we present the elementary assumptions of our research on the
role of the magnetic field in modelling the quiescence-outbursts cycle in
Cataclysmic Variables (CVs). The behaviour of the magnetic field is crucial not
only to integrate the disk instability model (Osaki 1974), but also to
determine the cause and effect nexus among parameters affecting the behavior of
complex systems. On the ground of our interpretation of the results emerging
from the literature, we suggest that in models describing DNe outbursts, such
as the disk instability model, the secondary instability model (Bath 1973) and
the thermonuclear runaway model (Mitrofanov 1978), the role of the magnetic
field is at least twofold. On the one hand, it activates a specific dynamic
pathway for the accreting matter by channelling it. On the other hand, it could
be indirectly responsible for switching a particular outburst modality. In
order to represent these two roles of the magnetic field, we need to integrate
the disk instability model by looking at the global behaviour of the system
under analysis. Stochastic resonance in dynamo models, we believe, is a
suitable candidate for accomplishing this task. We shall present the MHD model
including this mechanism elsewhere.Comment: 5 pages, 2 figures, CTU Proceedings, Acta Polytechnica (accepted
Polar features in the flagellar propulsion of E. coli bacteria
E. coli bacteria swim following a run and tumble pattern. In the run state
all flagella join in a single helical bundle that propels the cell body along
approximately straight paths. When one or more flagellar motors reverse
direction the bundle unwinds and the cell randomizes its orientation. This
basic picture represents an idealization of a much more complex dynamical
problem. Although it has been shown that bundle formation can occur at either
pole of the cell, it is still unclear whether this two run states correspond to
asymmetric propulsion features. Using holographic microscopy we record the 3D
motions of individual bacteria swimming in optical traps. We find that most
cells possess two run states characterised by different propulsion forces,
total torque and bundle conformations. We analyse the statistical properties of
bundle reversal and compare the hydrodynamic features of forward and backward
running states. Our method is naturally multi-particle and opens up the way
towards controlled hydrodynamic studies of interacting swimming cells
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