35,510 research outputs found
Discovery and Identification of W' and Z' in SU(2) x SU(2) x U(1) Models at the LHC
We explore the discovery potential of W' and Z' boson searches for various
SU(2) x SU(2) x U(1) models at the Large Hadron Collider (LHC), after taking
into account the constraints from low energy precision measurements and direct
searches at both the Tevatron (1.96 TeV) and the LHC (7 TeV). In such models,
the W' and Z' bosons emerge after the electroweak symmetry is spontaneously
broken. Two patterns of the symmetry breaking are considered in this work: one
is SU(2)_L x SU(2)_2 x U(1)_X to SU(2)_L x U(1)_Y (BP-I), another is SU(2)_1 x
SU(2)_2 x U(1)_Y to SU(2)_L x U(1)_Y (BP-II). Examining the single production
channel of W' and Z' with their subsequent leptonic decays, we find that the
probability of detecting W' and Z' bosons in the considered models at the LHC
(with 14 TeV) is highly limited by the low energy precision data constraints.
We show that observing Z' alone, without seeing a W', does not rule out new
physics models with non-Abelian gauge extension, such as the phobic models in
BP-I. Models in BP-II would predict the discovery of degenerate W' and Z'
bosons at the LHC.Comment: 29 pages, including 11 figures, 3 tables, added references for
introductio
Supernova Constraints on Models of Neutrino Dark Energy
In this paper we use the recently released Type Ia Supernova (SNIa) data to
constrain the interactions between the neutrinos and the dark energy scalar
fields. In the analysis we take the dark energy scalars to be either
Quintessence-like or Phantom-like. Our results show the data mildly favor a
model where the neutrinos couple to a phantom-like dark energy scalar, which
implies the equation of state of the coupled system behaves like Quintom
scenario in the sense of parameter degeneracy. We find future observations like
SNAP are potentially promising to measure the couplings between neutrino and
dark energy.Comment: Typos fixed and references updated. Version pressed in PR
Augmenting the Calvin-Benson-Bassham cycle by a synthetic malyl-CoA-glycerate carbon fixation pathway.
The Calvin-Benson-Bassham (CBB) cycle is presumably evolved for optimal synthesis of C3 sugars, but not for the production of C2 metabolite acetyl-CoA. The carbon loss in producing acetyl-CoA from decarboxylation of C3 sugar limits the maximum carbon yield of photosynthesis. Here we design a synthetic malyl-CoA-glycerate (MCG) pathway to augment the CBB cycle for efficient acetyl-CoA synthesis. This pathway converts a C3 metabolite to two acetyl-CoA by fixation of one additional CO2 equivalent, or assimilates glyoxylate, a photorespiration intermediate, to produce acetyl-CoA without net carbon loss. We first functionally demonstrate the design of the MCG pathway in vitro and in Escherichia coli. We then implement the pathway in a photosynthetic organism Synechococcus elongates PCC7942, and show that it increases the intracellular acetyl-CoA pool and enhances bicarbonate assimilation by roughly 2-fold. This work provides a strategy to improve carbon fixation efficiency in photosynthetic organisms
Maximum likelihood reconstruction for Ising models with asynchronous updates
We describe how the couplings in an asynchronous kinetic Ising model can be
inferred. We consider two cases, one in which we know both the spin history and
the update times and one in which we only know the spin history. For the first
case, we show that one can average over all possible choices of update times to
obtain a learning rule that depends only on spin correlations and can also be
derived from the equations of motion for the correlations. For the second case,
the same rule can be derived within a further decoupling approximation. We
study all methods numerically for fully asymmetric Sherrington-Kirkpatrick
models, varying the data length, system size, temperature, and external field.
Good convergence is observed in accordance with the theoretical expectations
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