2,124 research outputs found
Renormalization of minimally doubled fermions
We investigate the renormalization properties of minimally doubled fermions,
at one loop in perturbation theory. Our study is based on the two particular
realizations of Borici-Creutz and Karsten-Wilczek. A common feature of both
formulations is the breaking of hyper-cubic symmetry, which requires that the
lattice actions are supplemented by suitable counterterms. We show that three
counterterms are required in each case and determine their coefficients to one
loop in perturbation theory. For both actions we compute the vacuum
polarization of the gluon. It is shown that no power divergences appear and
that all contributions which arise from the breaking of Lorentz symmetry are
cancelled by the counterterms. We also derive the conserved vector and
axial-vector currents for Karsten-Wilczek fermions. Like in the case of the
previously studied Borici-Creutz action, one obtains simple expressions,
involving only nearest-neighbour sites. We suggest methods how to fix the
coefficients of the counterterms non-perturbatively and discuss the
implications of our findings for practical simulations.Comment: 23 pages, 1 figur
The Origin of Mass
The quark-lepton mass problem and the ideas of mass protection are reviewed.
The hierarchy problem and suggestions for its resolution, including Little
Higgs models, are discussed. The Multiple Point Principle is introduced and
used within the Standard Model to predict the top quark and Higgs particle
masses. Mass matrix ans\"{a}tze are considered; in particular we discuss the
lightest family mass generation model, in which all the quark mixing angles are
successfully expressed in terms of simple expressions involving quark mass
ratios. It is argued that an underlying chiral flavour symmetry is responsible
for the hierarchical texture of the fermion mass matrices. The phenomenology of
neutrino mass matrices is briefly discussed.Comment: 33 pages, 7 figures, to be published in the Proceedings of the XXXI
ITEP Winter School, Moscow, Russia, 18 - 26 February 200
Sustainable bioethanol production combining biorefinery principles using combined raw materials from wheat undersown with clover-grass
To obtain the best possible net energy balance of the bioethanol production the biomass raw materials used need to be produced with limited use of non-renewable fossil fuels. Intercropping strategies are known to maximize growth and productivity by including more than one species in the crop stand, very often with legumes as one of the components. In the present study clover-grass is undersown in a traditional wheat crop. Thereby, it is possible to increase input of symbiotic fixation of atmospheric nitrogen into the cropping systems and reduce the need for fertilizer applications. Furthermore, when using such wheat and clover-grass mixtures as raw material, addition of urea and other fermentation nutrients produced from fossil fuels can be reduced in the whole ethanol manufacturing chain. Using second generation ethanol technology mixtures of relative proportions of wheat straw and clover-grass (15:85, 50:50, and 85:15) were pretreated by wet oxidation. The results showed that supplementing wheat straw with clover-grass had a positive effect on the ethanol yield in simultaneous saccharification and fermentation experiments, and the effect was more pronounced in inhibitory substrates. The highest ethanol yield (80% of theoretical) was obtained in the experiment with high fraction (85%) of clover-grass. In order to improve the sugar recovery of clover-grass, it should be separated into a green juice (containing free sugars, fructan, amino acids, vitamins and soluble minerals) for direct fermentation and a fibre pulp for pretreatment together with wheat straw. Based on the obtained results a decentralized biorefinery concept for production of biofuel is suggested emphasizing sustainability, localness, and recycling principle
Effective String Theory and Nonlinear Lorentz Invariance
We study the low-energy effective action governing the transverse
fluctuations of a long string, such as a confining flux tube in QCD. We work in
the static gauge where this action contains only the transverse excitations of
the string. The static gauge action is strongly constrained by the requirement
that the Lorentz symmetry, that is spontaneously broken by the long string
vacuum, is nonlinearly realized on the Nambu-Goldstone bosons. One solution to
the constraints (at the classical level) is the Nambu-Goto action, and the
general solution contains higher derivative corrections to this. We show that
in 2+1 dimensions, the first allowed correction to the Nambu-Goto action is
proportional to the squared curvature of the induced metric on the worldsheet.
In higher dimensions, there is a more complicated allowed correction that
appears at lower order than the curvature squared. We argue that this leading
correction is similar to, but not identical to, the one-loop determinant
(\sqrt{-h} R \Box^{-1} R) computed by Polyakov for the bosonic fundamental
string.Comment: 15 page
The Fluctuations of the Quark Number and of the Chiral Condensate
The distributions of the quark number and chiral condensate over the gauge
fields are computed for QCD in Euclidean space at nonzero quark chemical
potential. As both operators are non-hermitian the distributions are in the
complex plane. Moreover, because of the sign problem, the distributions are not
real and positive. The computations are carried out within leading order chiral
perturbation theory and give a direct insight into the delicate cancellations
that take place in contributions to the total baryon number and the chiral
condensate.Comment: 19 pages, 2 figure
Open/Closed String Topology and Moduli Space Actions via Open/Closed Hochschild Actions
In this paper we extend our correlation functions to the open/closed case.
This gives rise to actions of an open/closed version of the Sullivan PROP as
well as an action of the relevant moduli space. There are several unexpected
structures and conditions that arise in this extension which are forced upon us
by considering the open sector. For string topology type operations, one cannot
just consider graphs, but has to take punctures into account and one has to
restrict the underlying Frobenius algebras. In the moduli space, one first has
to pass to a smaller moduli space which is closed under open/closed duality and
then consider covers in order to account for the punctures
More On The Connection Between Planar Field Theory And String Theory
We continue work on the connection between world sheet representation of the
planar phi^3 theory and string formation. The present article, like the earlier
work, is based on the existence of a solitonic solution on the world sheet, and
on the zero mode fluctuations around this solution. The main advance made in
this paper is the removal of the cutoff and the transition to the continuum
limit on the world sheet. The result is an action for the modes whose energies
remain finite in this limit (light modes). The expansion of this action about a
dense background of graphs on the world sheet leads to the formation of a
string.Comment: 27 pages, 3 figure
Field Theory On The World Sheet: Improvements And Generalizations
This article is the continuation of a project of investigating planar phi^3
model in various dimensions. The idea is to reformulate them on the world
sheet, and then to apply the classical (meanfield) approximation, with two
goals: To show that the ground state of the model is a solitonic configuration
on the world sheet, and the quantum fluctuations around the soliton lead to the
formation of a transverse string. After a review of some of the earlier work,
we introduce and discuss several generalizations and new results. In 1+2
dimensions, a rigorous upper bound on the solitonic energy is established. A
phi^4 interaction is added to stabilize the original phi^3 model. In 1+3 and
1+5 dimensions, an improved treatment of the ultraviolet divergences is given.
And significantly, we show that our approximation scheme can be imbedded into a
systematic strong coupling expansion. Finally, the spectrum of quantum
fluctuations around the soliton confirms earlier results: In 1+2 and 1+3
dimensions, a transverse string is formed on the world sheet.Comment: 29 pages, 5 figures, several typos and eqs.(74) and (75) are
corrected, a comment added to section
- …