240 research outputs found
One-loop matching for quark dipole operators in a gradient-flow scheme
The quark chromoelectric dipole (qCEDM) operator is a CP-violating operator describing, at hadronic energies, beyond-the-standard-model contributions to the electric dipole moment of particles with nonzero spin. In this paper we define renormalized dipole operators in a regularization-independent scheme using the gradient flow, and we perform the matching at one loop in perturbation theory to renormalized operators of the same and lower dimension in the more familiar MS scheme. We also determine the matching coefficients for the quark chromo-magnetic dipole operator (qCMDM), which contributes for example to matrix elements relevant to CP-violating and CP-conserving kaon decays. The calculation provides a basis for future lattice QCD computations of hadronic matrix elements of the qCEDM and qCMDM operators
One-loop matching of the CP-odd three-gluon operator to the gradient flow
The calculation of the neutron electric dipole moment within effective field theories for physics beyond the Standard Model requires non-perturbative hadronic matrix elements of effective operators composed of quark and gluon fields. In order to use input from lattice computations, these matrix elements must be translated from a scheme suitable for lattice QCD to the minimal-subtraction scheme used in the effective-field-theory framework. The accuracy goal in the context of the neutron electric dipole moment necessitates at least a one-loop matching calculation. Here, we provide the one-loop matching coefficients for the CP-odd three-gluon operator between two different minimally subtracted 't HooftâVeltman schemes and the gradient flow. This completes our program to obtain the one-loop gradient-flow matching coefficients for all CP-violating and flavor-conserving operators in the low-energy effective field theory up to dimension six
The continuum limit of the static-light meson spectrum
We investigate the continuum limit of the low lying static-light meson
spectrum using Wilson twisted mass lattice QCD with N_f = 2 dynamical quark
flavours. We consider three values of the lattice spacing a ~ 0.051 fm, 0.064
fm, 0.080 fm and various values of the pion mass in the range 280 MeV < m_PS <
640 MeV. We present results in the continuum limit for light cloud angular
momentum j = 1/2, 3/2, 5/2 and for parity P = +, -. We extrapolate our results
to physical quark masses, make predictions regarding the spectrum of B and B_s
mesons and compare with available experimental results.Comment: 18 pages, 3 figure
A Perfect Script? Manchester United's Class of â92
The Class of â92 is a documentary film featuring six Manchester United F.C. players who recount their time during a pivotal period for the club, English football and English society. The documentary claims to offer a commentary on Britain in the 1990s, but appears, without acknowledging the fact, to be a promotional vehicle to establish the six men as a brand labeled the Class of â92 (CO92). Creating this brand necessarily involved presenting a selective account of their time and places with the film being little more than an advertisement, masquerading as an observational documentary. The film draws freely upon the symbolic capital held by the club and the city of Manchester and uses the Busby Babes/Munich chapter and the more recent âMadchester sceneâ to forge the Class of â92 brand by editing out those elements that did not accord with this project. The article argues that a more complete representation of â90s Britain, while disrupting the intended narrative, would acknowledge the significant structural and commercial changes experienced by the club, the sport, and the city in the last decade of the 20th century. We suggest that the Class of â92 invites the viewer to consider how the documentary film genre can contribute to brand development and promotion
Lattice QCD determination of m_b, f_B and f_Bs with twisted mass Wilson fermions
We present a lattice QCD determination of the b quark mass and of the B and
B_s decay constants, performed with N_f=2 twisted mass Wilson fermions, by
simulating at four values of the lattice spacing. In order to study the b quark
on the lattice, two methods are adopted in the present work, respectively based
on suitable ratios with exactly known static limit and on the interpolation
between relativistic data, evaluated in the charm mass region, and the static
point, obtained by simulating the HQET on the lattice. The two methods provide
results in good agreement. For the b quark mass in the MSbar scheme and for the
decay constants we obtain m_b(m_b)=4.29(14) GeV, f_B=195(12) MeV, f_Bs=232(10)
MeV and f_Bs/f_B=1.19(5). As a byproduct of the analysis we also obtain the
results for the f_D and f_Ds decay constants: f_D=212(8) MeV, f_Ds=248(6) MeV
and f_Ds/f_D=1.17(5).Comment: 23 pages, 10 figures, 2 tables. Added appendix showing the agreement
of the data for the ratios with the HQE prediction. Matching JHEP published
versio
Enterprise Education Competitions: A Theoretically Flawed Intervention?
The demand for including enterprise in the education system, at all levels and for all pupils is now a global phenomenon. Within this context, the use of competitions and competitive learning activities is presented as a popular and effective vehicle for learning. The purpose of this chapter is to illustrate how a realist method of enquiry â which utilises theory as the unit of analysis â can shed new light on the assumed and unintended outcomes of enterprise education competitions. The case developed here is that there are inherent flaws in assuming that competitions will âworkâ in the ways set out in policy and guidance. Some of the most prevalent stated outcomes â that competitions will motivate and reward young people, that they will enable the development of entrepreneurial skills, and that learners will be inspired by their peers â are challenged by theory from psychology and education. The issue at stake is that the expansion of enterprise education policy into primary and secondary education increases the likelihood that more learners will be sheep dipped in competitions, and competitive activities, without a clear recognition of the potential unintended effects. In this chapter, we employ a realist-informed approach to critically evaluate the theoretical basis that underpins the use of competitions and competitive learning activities in school-based enterprise education. We believe that our findings and subsequent recommendations will provide those who promote and practice the use of competitions with a richer, more sophisticated picture of the potential flaws within such activities.Peer reviewedFinal Published versio
Individual Eigenvalue Distributions for the Wilson Dirac Operator
We derive the distributions of individual eigenvalues for the Hermitian
Wilson Dirac Operator D5 as well as for real eigenvalues of the Wilson Dirac
Operator DW. The framework we provide is valid in the epsilon regime of chiral
perturbation theory for any number of flavours Nf and for non-zero low energy
constants W6, W7, W8. It is given as a perturbative expansion in terms of the
k-point spectral density correlation functions and integrals thereof, which in
some cases reduces to a Fredholm Pfaffian. For the real eigenvalues of DW at
fixed chirality nu this expansion truncates after at most nu terms for small
lattice spacing "a". Explicit examples for the distribution of the first and
second eigenvalue are given in the microscopic domain as a truncated expansion
of the Fredholm Pfaffian for quenched D5, where all k-point densities are
explicitly known from random matrix theory. For the real eigenvalues of
quenched DW at small "a" we illustrate our method by the finite expansion of
the corresponding Fredholm determinant of size nu.Comment: 20 pages, 5 figures; v2: typos corrected, refs added and discussion
of W6 and W7 extende
Random Matrix Theory for the Hermitian Wilson Dirac Operator and the chGUE-GUE Transition
We introduce a random two-matrix model interpolating between a chiral
Hermitian (2n+nu)x(2n+nu) matrix and a second Hermitian matrix without
symmetries. These are taken from the chiral Gaussian Unitary Ensemble (chGUE)
and Gaussian Unitary Ensemble (GUE), respectively. In the microscopic large-n
limit in the vicinity of the chGUE (which we denote by weakly non-chiral limit)
this theory is in one to one correspondence to the partition function of Wilson
chiral perturbation theory in the epsilon regime, such as the related two
matrix-model previously introduced in refs. [20,21]. For a generic number of
flavours and rectangular block matrices in the chGUE part we derive an
eigenvalue representation for the partition function displaying a Pfaffian
structure. In the quenched case with nu=0,1 we derive all spectral correlations
functions in our model for finite-n, given in terms of skew-orthogonal
polynomials. The latter are expressed as Gaussian integrals over standard
Laguerre polynomials. In the weakly non-chiral microscopic limit this yields
all corresponding quenched eigenvalue correlation functions of the Hermitian
Wilson operator.Comment: 27 pages, 4 figures; v2 typos corrected, published versio
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