6,195 research outputs found
New Discrete States in Two-Dimensional Supergravity
Two-dimensional string theory is known to contain the set of discrete states
that are the SU(2) multiplets generated by the lowering operator of the SU(2)
current algebra.Their structure constants are defined by the area preserving
diffeomorphisms in two dimensions. We show that the interaction of
superstrings with the superconformal ghosts enlarges the algebra of dimension 1
currents and hence the new discrete states appear. These new states are the
SU(N) multiplets, if the algebra includes the currents of ghost numbers from -N
to N-2, not related by the picture-changing. We compute the structure constants
of these new discrete states for N=3 and express them in terms of SU(3)
Clebsch-Gordan coefficients,relating their operator algebra to the volume
preserving diffeomorphisms in d=3. For general N, the algebra is conjectured to
be isomorphic to SDiff(N). This points at possible holographic relations
between 2d superstrings and field theories in higher dimensions.Comment: 22 pages; typos corrected, 2 references adde
Mobile impurities in integrable models
We use a mobile impurity or depleton model to study elementary excitations in
one-dimensional integrable systems. For Lieb-Liniger and bosonic Yang-Gaudin
models we express two phenomenological parameters characterising renormalised
inter- actions of mobile impurities with superfluid background: the number of
depleted particles, and the superfluid phase drop in terms of the
corresponding Bethe Ansatz solution and demonstrate, in the leading order, the
absence of two-phonon scattering resulting in vanishing rates of inelastic
processes such as viscosity experienced by the mobile impuritiesComment: 25 pages, minor corrections made to the manuscrip
A Teacher in the Living Room? Educational Media for Babies, Toddlers, and Preschoolers
Examines available research, and arguments by proponents and critics, of electronic educational media use by young children. Examines educational claims in marketing and provides recommendations for developing research and product standards
Parallax and masses of alpha Centauri revisited
Context. Despite the thorough work of van Leeuwen (2007), the parallax of
alpha Centauri is still far from being carved in stone. Any derivation of the
individual masses is therefore uncertain, if not questionable. And yet, that
does not prevent this system from being used for calibration purpose in several
studies. Aims. Obtaining more accurate model-free parallax and individual
masses of this system. Methods. With HARPS, the radial velocities are not only
precise but also accurate. Ten years of HARPS data are enough to derive the
complement of the visual orbit for a full 3D orbit of alpha Cen. Results. We
locate alpha Cen (743 mas) right where Hipparcos (ESA 1997) had put it, i.e.
slightly further away than derived by Soderhjelm (1999). The components are
thus a bit more massive than previously thought (1.13 and 0.97 Msun for A and B
respectively). These values are now in excellent agreement with the latest
asteroseismologic results.Comment: 4 pages, 3 figures, accepted in Astronomy & Astrophysic
Comment on "Kinetic theory for a mobile impurity in a degenerate Tonks-Girardeau gas"
In a recent paper, arxiv:1402.6362, Gamayun, Lychkovskiy, and Cheianov
studied the dynamics of a mobile impurity embedded into a one-dimensional
Tonks-Girardeau gas of strongly interacting bosons. Employing the Boltzmann
equation approach, they arrived at the following main conclusions: (i) a light
impurity, being accelerated by a constant force does not exhibit Bloch
oscillations; (ii) a heavy impurity does undergo Bloch oscillations,
accompanied by a drift with the velocity proportional to the square root of
force. In this comment we argue that the result (i) is an artifact of the
classical Boltzmann approximation, which misses the formation of the (quasi)
bound-state between the impurity and a hole. Result (ii), while not valid at
asymptotically small force, indeed reflects an interesting intermediate-force
behavior. Here we clarify its limits of applicability and extend beyond the
Tonks-Girardeau limit.Comment: 2 pages, 1 figur
A Model of Persuasion - With Implications for Financial Markets
We propose a model of the phenomenon of persuasion. We argue that individual beliefs evolve in a way that overweights the opinions and information of individuals whom they "listen to" relative to other individuals. Such agents can be understood to be acting as though they believe they listen to a representative sample of the individuals with valuable information, even though they may not. We analyze dynamics and convergence of beliefs, characterizing when agents' beliefs converge over time to the same beliefs, and when they instead diverge. Convergent beliefs can be characterized as the weighted average of agents' initial beliefs, and these weights can be interpreted as a measure of ``influence.'' We then explore implications in an asset trading setting. Here we demonstrate that agents profit from being influential as well as being accurate. When agents' choice of whom to listen to is endogenous, we show that an individual's influence can be persistent, even though the individual may be inaccurate.
Persuasion bias, social influence, and uni-dimensional opinions.
We propose a boundedly rational model of opinion formation in which individuals are subject to persuasion bias; that is, they fail to account for possible repetition in the information they receive. We show that persuasion bias implies the phenomenon of social influence, whereby oneâs influence on group opinions depends not only on accuracy, but also on how well-connected one is in the social network that determines communication. Persuasion bias also implies the phenomenon of unidimensional opinions; that is, individualsâ opinions over a multidimensional set of issues converge to a single âleft-rightâ spectrum. We explore the implications of our model in several natural settings, including political science and marketing, and we obtain a number of novel empirical implications.
The multiplicity of \phi\ Phe revisited
The chemically peculiar B star Phe was, until very recently,
considered a triple system, even though the data were not conclusive and the
orbits rather uncertain. Very recent results by Korhonen et al. (2013) provided
a revised orbit, different from the then available astrometric Hipparcos orbit.
Additional spectroscopic data, obtained with the BESO spectrograph at Cerro
Armazones, confirm the newly found orbit, even though the resulting radial
velocities do not allow to improve on the recent orbit. We combine the latter
with the Hipparcos measurements to secure the astrometric orbit, and derive the
inclination of the system. Using evolutionary tracks, we can finally constrain
all the parameters of the two components in this system.
We confirm the mass of the primary, 3 M, and find that the companion
has a mass of 0.9 M. The inclination of the system is , and is potentially eclipsing; we predict the time of the next
conjunction. Given that the eccentricity of the orbit and the exact value of
the semi-amplitude of the radial velocity relies on just one set of points, we
also urge observers to measure radial velocities at the next periastron passage
in April 2015.Comment: 5 papes, accepted as Research Note in Astronomy and Astrophysic
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