20,366 research outputs found
Almost-Commutative Geometries Beyond the Standard Model III: Vector Doublets
We will present a new extension of the standard model of particle physics in
its almostcommutative formulation. This extension has as its basis the algebra
of the standard model with four summands [11], and enlarges only the particle
content by an arbitrary number of generations of left-right symmetric doublets
which couple vectorially to the U(1)_YxSU(2)_w subgroup of the standard model.
As in the model presented in [8], which introduced particles with a new colour,
grand unification is no longer required by the spectral action. The new model
may also possess a candidate for dark matter in the hundred TeV mass range with
neutrino-like cross section
Almost-Commutative Geometries Beyond the Standard Model II: New Colours
We will present an extension of the standard model of particle physics in its
almost-commutative formulation. This extension is guided by the minimal
approach to almost-commutative geometries employed in [13], although the model
presented here is not minimal itself.
The corresponding almost-commutative geometry leads to a Yang-Mills-Higgs
model which consists of the standard model and two new fermions of opposite
electro-magnetic charge which may possess a new colour like gauge group. As a
new phenomenon, grand unification is no longer required by the spectral action.Comment: Revised version for publication in J.Phys.A with corrected Higgs
masse
Almost-Commutative Geometries Beyond the Standard Model
In [7-9] and [10] the conjecture is presented that almost-commutative
geometries, with respect to sensible physical constraints, allow only the
standard model of particle physics and electro-strong models as
Yang-Mills-Higgs theories. In this publication a counter example will be given.
The corresponding almost-commutative geometry leads to a Yang-Mills-Higgs
model which consists of the standard model of particle physics and two new
fermions of opposite electro-magnetic charge. This is the second
Yang-Mills-Higgs model within noncommutative geometry, after the standard
model, which could be compatible with experiments. Combined to a hydrogen-like
composite particle these new particles provide a novel dark matter candidate
Bootstrap union tests for unit roots in the presence of nonstationary volatility
We provide a joint treatment of three major issues that surround testing for a unit root in practice: uncertainty as to whether or not a linear deterministic trend is present in the data, uncertainty as to whether the initial condition of the process is (asymptotically) negligible or not, and the possible presence of nonstationary volatility in the data. Harvey, Leybourne and Taylor (2010, Journal of Econometrics, forthcoming) propose decision rules based on a four-way union of rejections of QD and OLS detrended tests, both with and without allowing for a linear trend, to deal with the first two problems. However, in the presence of nonstationary volatility these test statistics have limit distributions which depend on the form of the volatility process, making tests based on the standard asymptotic critical values invalid. We construct bootstrap versions of the four-way union of rejections test, which, by employing the wild bootstrap, are shown to be asymptotically valid in the presence of nonstationary volatility. These bootstrap union tests therefore allow for a joint treatment of all three of the aforementioned problems.Unit root; local trend; initial condition; asymptotic power; union of rejections decision rule; nonstationary volatility; wild bootstrap
Estimating the COGARCH(1,1) model - a first go
We suggest moment estimators for the parameters of a continuous time GARCH(1,1) process based on equally spaced observations. Using the fact that the increments of the COGARCH(1,1) process are ergodic, the resulting estimators are consistent. We investigate the quality of our estimators in a simulation study based on the compound Poisson driven COGARCH model. The estimated volatility with corresponding residual analysis is also presented
A Top-down and Bottom-up look at Emissions Abatement in Germany in response to the EU ETS
This paper uses top-down trend analysis and a bottom-up power sector model to define upper and lower boundaries on abatement in Germany in the first phase of the EU Emissions Trading Scheme (2005-2007). Long-term trend analysis reveals the decoupling of economic activity and carbon emissions in Germany that has occurred since 1996 and has accelerated since 2005, in response to rising commodities prices, the introduction of a carbon trading, and other measures undertaken in Germany. Differing emission intensity trends and emissions counterfactuals are constructed using emissions, power generation, and macroeconomic data. Resulting top-down estimates set the upper bound of abatement in Phase I at 121.9 mn tons for all EU-ETS sectors and 56.7 mn tons for the power sector only. Using the tuned version of the model “E-simulate” a lower boundary of Phase I abatement is established at 13.2 million tons, based only on fuel switching in the power sector, which constitutes 61% of German ETS sector emissions. The paper characterizes abatement, critically discusses the underlying assumptions of the outcomes, and examines the impact of two main factors on power sector abatement, namely price and load.Massachusetts Institute of Technology. Center for Energy and Environmental Policy Research
Quantum glass phases in the disordered Bose-Hubbard model
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal
disorder is determined using Quantum Monte Carlo simulations. A sequence of
quantum glass phases intervene at the interface between the Mott insulating and
the Superfluid phases of the clean system. In addition to the standard Bose
glass phase, the coexistence of gapless and gapped regions close to the Mott
insulating phase leads to a novel Mott glass regime which is incompressible yet
gapless. Numerical evidence for the properties of these phases is given in
terms of global (compressibility, superfluid stiffness) and local
(compressibility, momentum distribution) observables
Arithmetic complexity via effective names for random sequences
We investigate enumerability properties for classes of sets which permit
recursive, lexicographically increasing approximations, or left-r.e. sets. In
addition to pinpointing the complexity of left-r.e. Martin-L\"{o}f, computably,
Schnorr, and Kurtz random sets, weakly 1-generics and their complementary
classes, we find that there exist characterizations of the third and fourth
levels of the arithmetic hierarchy purely in terms of these notions.
More generally, there exists an equivalence between arithmetic complexity and
existence of numberings for classes of left-r.e. sets with shift-persistent
elements. While some classes (such as Martin-L\"{o}f randoms and Kurtz
non-randoms) have left-r.e. numberings, there is no canonical, or acceptable,
left-r.e. numbering for any class of left-r.e. randoms.
Finally, we note some fundamental differences between left-r.e. numberings
for sets and reals
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