13 research outputs found
Partonic transverse momenta in non-relativistic hyper-central quark potential models
We investigate the impact of three-body forces on the transverse-momentum
distribution of partons inside the proton. This is achieved by considering the
three-body problem in a class of hyper-central quark potential models. Solving
the corresponding Schr\"odinger equation, we determine the quark wave function
in the proton and with appropriate transformations and projections we find the
transverse-momentum distribution of a single quark. In each case the parameters
of the quark potentials are adjusted in order to sufficiently describe
observable properties of the proton. Using a factorization ansatz, we
incorporate the obtained transverse-momentum distribution in a perturbative QCD
scheme for the calculation of the cross-section for prompt photon production in
pp collisions. A large set of experimental data is fitted using as a single
free parameter the mean partonic transverse momentum. The dependence of
on the collision characteristics (initial energy and transverse momentum of the
final photon) is much smoother when compared with similar results found in the
literature using a Gaussian distribution for the partonic transverse momenta.
Within the considered class of hyper-central quark potentials the one with the
weaker dependence on the hyper-radius is preferred for the description of the
data since it leads to the smoothest mean partonic transverse-momentum profile.
We have repeated all the calculations using a two-body potential of the same
form as the optimal (within the considered class) hyper-central potential in
order to check if the presence of three-body forces is supported by the
experimental data. Our analysis indicates that three-body forces influence
significantly the form of the parton transverse-momentum distribution and
consequently lead to an improved description of the considered data.Comment: 8 pages, 7 figure
Entanglement entropies and fermion signs of critical metals
The fermion sign problem is often viewed as a sheer inconvenience that
plagues numerical studies of strongly interacting electron systems. Only
recently, it has been suggested that fermion signs are fundamental for the
universal behavior of critical metallic systems and crucially enhance their
degree of quantum entanglement. In this work we explore potential connections
between emergent scale invariance of fermion sign structures and scaling
properties of bipartite entanglement entropies. Our analysis is based on a
wavefunction ansatz that incorporates collective, long-range backflow
correlations into fermionic Slater determinants. Such wavefunctions mimic the
collapse of a Fermi liquid at a quantum critical point. Their nodal surfaces --
a representation of the fermion sign structure in many-particle configurations
space -- show fractal behavior up to a length scale that diverges at a
critical backflow strength. We show that the Hausdorff dimension of the fractal
nodal surface depends on , the number of fermions and the exponent of the
backflow. For the same wavefunctions we numerically calculate the second
R\'enyi entanglement entropy . Our results show a cross-over from volume
scaling, ( in dimensions), to the
characteristic Fermi-liquid behavior on scales larger
than . We find that volume scaling of the entanglement entropy is a robust
feature of critical backflow fermions, independent of the backflow exponent and
hence the fractal dimension of the scale invariant sign structure.Comment: 9.5 pages, 10 figure
Holographic fermions at strong translational symmetry breaking: a Bianchi-VII case study
It is presently unknown how strong lattice potentials influence the fermion
spectral function of the holographic strange metals predicted by the AdS/CFT
correspondence. This embodies a crucial test for the application of holography
to condensed matter experiments. We show that for one particular momentum
direction this spectrum can be computed for arbitrary strength of the effective
translational symmetry breaking potential of the so-called Bianchi-VII geometry
employing ordinary differential equations. Deep in the strange metal regime we
find rather small changes to the single-fermion response computed by the
emergent quantum critical IR, even when the potential becomes relevant in the
infra-red. However, in the regime where holographic quasi-particles occur,
defining a Fermi surface in the continuum, they acquire a finite lifetime at
any finite potential strength. At the transition from irrelevancy to relevancy
of the Bianchi potential in the deep infra-red the quasi-particle remnants
disappear completely and the fermion spectrum exhibits a purely relaxational
behaviour.Comment: 30 pages, 10 figure
Age, period, and cohort analysis of regular dental care behavior and edentulism: A marginal approach
<p>Abstract</p> <p>Background</p> <p>To analyze the regular dental care behavior and prevalence of edentulism in adult Danes, reported in sequential cross-sectional oral health surveys by the application of a marginal approach to consider the possible clustering effect of birth cohorts.</p> <p>Methods</p> <p>Data from four sequential cross-sectional surveys of non-institutionalized Danes conducted from 1975-2005 comprising 4330 respondents aged 15+ years in 9 birth cohorts were analyzed. The key study variables were seeking dental care on an annual basis (ADC) and edentulism. For the analysis of ADC, survey year, age, gender, socio-economic status (SES) group, denture-wearing, and school dental care (SDC) during childhood were considered. For the analysis of edentulism, only respondents aged 35+ years were included. Survey year, age, gender, SES group, ADC, and SDC during childhood were considered as the independent factors. To take into account the clustering effect of birth cohorts, marginal logistic regressions with an independent correlation structure in generalized estimating equations (GEE) were carried out, with PROC GENMOD in SAS software.</p> <p>Results</p> <p>The overall proportion of people seeking ADC increased from 58.8% in 1975 to 86.7% in 2005, while for respondents aged 35 years or older, the overall prevalence of edentulism (35+ years) decreased from 36.4% in 1975 to 5.0% in 2005. Females, respondents in the higher SES group, in more recent survey years, with no denture, and receiving SDC in all grades during childhood were associated with higher probability of seeking ADC regularly (<it>P </it>< 0.05). The interaction of SDC and age (<it>P </it>< 0.0001) was significant. The probabilities of seeking ADC were even higher among subjects with SDC in all grades and aged 45 years or older. Females, older age group, respondents in earlier survey years, not seeking ADC, lower SES group, and not receiving SDC in all grades were associated with higher probability of being edentulous (<it>P </it>< 0.05).</p> <p>Conclusions</p> <p>With the use of GEE, the potential clustering effect of birth cohorts in sequential cross-sectional oral health survey data could be appropriately considered. The success of Danish dental health policy was demonstrated by a continued increase of regular dental visiting habits and tooth retention in adults because school dental care was provided to Danes in their childhood.</p