1,131 research outputs found
Supersymmetric Models with Higher Dimensional Operators
In 4D renormalisable theories, integrating out massive states generates in
the low energy effective action higher dimensional operators (derivative or
otherwise). Using a superfield language it is shown that a 4D N=1
supersymmetric theory with higher derivative operators in either the Kahler or
the superpotential part of the Lagrangian and with an otherwise arbitrary
superpotential, is equivalent to a 4D N=1 theory of second order (i.e. without
higher derivatives) with additional superfields and renormalised interactions.
We provide examples where a free theory with trivial supersymmetry breaking
provided by a linear superpotential becomes, in the presence of higher
derivatives terms and in the second order version, a non-trivial interactive
one with spontaneous supersymmetry breaking. The couplings of the equivalent
theory acquire a threshold correction through their dependence on the scale of
the higher dimensional operator(s). The scalar potential in the second order
theory is not necessarily positive definite, and one can in principle have a
vanishing potential with broken supersymmetry. We provide an application to
MSSM and argue that at tree-level and for a mass scale associated to a higher
derivative term in the TeV range, the Higgs mass can be lifted above the
current experimental limits.Comment: 36 pages; some clarifications and references adde
Higher Derivative Operators from Scherk-Schwarz Supersymmetry Breaking on T^2/Z_2
In orbifold compactifications on T^2/Z_2 with Scherk-Schwarz supersymmetry
breaking, it is shown that (brane-localised) superpotential interactions and
(bulk) gauge interactions generate at one-loop higher derivative counterterms
to the mass of the brane (or zero-mode of the bulk) scalar field. These
brane-localised operators are generated by integrating out the bulk modes of
the initial theory which, although supersymmetric, is nevertheless
non-renormalisable. It is argued that such operators, of non-perturbative
origin and not protected by non-renormalisation theorems, are generic in
orbifold compactifications and play a crucial role in the UV behaviour of the
two-point Green function of the scalar field self-energy. Their presence in the
action with unknown coefficients prevents one from making predictions about
physics at (momentum) scales close to/above the compactification scale(s). Our
results extend to the case of two dimensional orbifolds, previous findings for
S^1/Z_2 and S^1/(Z_2 x Z_2') compactifications where brane-localised higher
derivative operators are also dynamically generated at loop level, regardless
of the details of the supersymmetry breaking mechanism. We stress the
importance of these operators for the hierarchy and the cosmological constant
problems in compactified theories.Comment: 23 pages, LaTeX, one figure, published version in JHE
The Self-Dual String and Anomalies in the M5-brane
We study the anomalies of a charge self-dual string solution in the
Coulomb branch of M5-branes. Cancellation of these anomalies allows us to
determine the anomaly of the zero-modes on the self-dual string and their
scaling with and . The dimensional reduction of the five-brane
anomalous couplings then lead to certain anomalous couplings for D-branes.Comment: 13 pages, Harvmac, refs adde
Toward an integrated approach to perception and action: conference report and future directions
This article was motivated by the conference entitled “Perception & Action – An Interdisciplinary Approach to Cognitive Systems Theory,” which took place September 14–16, 2010 at the Santa Fe Institute, NM, USA. The goal of the conference was to bring together an interdisciplinary group of neuroscientists, roboticists, and theorists to discuss the extent and implications of action–perception integration in the brain. The motivation for the conference was the realization that it is a widespread approach in biological, theoretical, and computational neuroscience to investigate sensory and motor function of the brain in isolation from one another, while at the same time, it is generally appreciated that sensory and motor processing cannot be fully separated. Our article summarizes the key findings of the conference, provides a hypothetical model that integrates the major themes and concepts presented at the conference, and concludes with a perspective on future challenges in the field
Progress in Absorber R&D for Muon Cooling
A stored-muon-beam neutrino factory may require transverse ionization cooling
of the muon beam. We describe recent progress in research and development on
energy absorbers for muon-beam cooling carried out by a collaboration of
university and laboratory groups.Comment: 7 pages, 1 figure, presented at the 3rd International Workshop on
Neutrino Factory Based on Muon Storage Rings (NuFACT'01), May 24-30, 2001,
Tsukuba, Japa
Recommended from our members
Issues for high-luminosity fixed-target rare-B-decay experiments
Fermilab E789 is the prototype of a new approach to the study of heavy-quark decays using fixed target. The apparatus acceptance is restricted to charged particles of relatively large momentum emerging at relatively large angles, allowing operation at high interaction rates. At rates up to 10 interactions per RF-bucket, the experiment may have sensitivity at the level of 10{sup {minus}6} per running period for such rare decay modes as B {yields} {pi}{sup +}{pi}{sup {minus}}. Could such an approach be extended to give sensitivity to standard-model CP violation in the beauty sector Since the predicted CP asymmetry in B {yields} {pi}{sup +}{pi}{sup {minus}} is of order 10{sup {minus}1}, this is a particularly attractive mode to consider. The simplest CP asymmetry would be a difference in absolute rates for B{sup 0} {yields} {pi}{sup +}{pi}{sup {minus}} and {ovr B{sup 0}} {yields} {pi}{sup +}{pi}{sup {minus}}, requiring tagging of the b-quark charge for its observation. Assuming a plausible branching ratio of 10{sup {minus}5} for B {yields} {pi}{sup +}{pi}{sup {minus}}, E789 should reconstruct some 30 events per run. In a restricted-acceptance experiment such as E789, the most plausible tagging technique is detection of single muons from semileptonic decay of the B. Since the B semileptonic branching ratios are {approx}10% and the E789 acceptance for muons from B decay is {approx}10%, fewer than 1 tagged event per run would be expected. We are thus looking for at least two orders of magnitude improvement in the produce luminosity {times} acceptance {times} tagging efficiency
Sub-Riemannian Calculus on Hypersurfaces in Carnot Groups
We develope basic geometric quantities and properties of hypersurfaces in
Carnot groups
Axion-photon Couplings in Invisible Axion Models
We reexamine the axion-photon couplings in various invisible axion models
motivated by the recent proposal of using optical interferometry at the ASST
facility in the SSCL to search for axion. We illustrate that the assignment of
charges for the fermion fields plays an important role in
determining the couplings. Several simple non-minimal invisible axion models
with suppressed and enhanced axion-photon couplings are constructed,
respectively. We also discuss the implications of possible new experiments to
detect solar axions by conversion to -rays in a static magnetic apparatus
tracking the sun.Comment: 14 pages, LaTeX fil
Measuring proper motions of isolated neutron stars with Chandra
The excellent spatial resolution of the Chandra observatory offers the
unprecedented possibility to measure proper motions at X-ray wavelength with
relatively high accuracy using as reference the background of extragalactic or
remote galactic X-ray sources. We took advantage of this capability to
constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray
bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and
lacking an optical counterpart. In this paper, we present results from a
preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and
138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022
respectively. We use these values together with those of other ROSAT discovered
INSs to constrain the origin, distance and evolutionary status of this
particular group of objects. We find that the tangential velocities of radio
quiet ROSAT neutron stars are probably consistent with those of 'normal'
pulsars. Their distribution on the sky and, for those having accurate proper
motion vectors, their possible birth places, all point to a local population,
probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in
the proceedings of "Isolated Neutron Stars: from the Interior to the
Surface", edited by D. Page, R. Turolla and S. Zan
- …