23,645 research outputs found
Macroscopic Screening of Coulomb Potentials From UV/IR-Mixing
We compute the static potential in a non-commutative theory including a term
due to UV/IR-mixing. As a result, the potential decays exponentially fast with
distance rather than like a power law Coulomb type potential due to the
exchange of massless particles. This shows that when quantum effects are taken
into account the introduction of non-commutativity not only modifies physics at
short distances but has dramatic macroscopic consequences as well. As a result,
we give a lower bound on the scale of non-commutativity (if present at all) to
be compatible with observations.Comment: 10 pages, V2 minor wording and reference
The Case for Future Hadron Colliders From Decays
Recent measurements in decays are somewhat
discrepant with Standard Model predictions. They may be harbingers of new
physics at an energy scale potentially accessible to direct discovery. We
estimate the sensitivity of future hadron colliders to the possible new
particles that may be responsible for the anomalies: leptoquarks or
s. We consider luminosity upgrades for a 14 TeV LHC, a 33 TeV LHC,
and a 100 TeV collider such as the FCC-hh. Coverage of models
is excellent: for narrow particles, with perturbative couplings that may
explain the -decay results for masses up to 20 TeV, a 33 TeV 1
ab LHC is expected to cover most of the parameter space up to 8 TeV in
mass, whereas the 100 TeV FCC-hh with 10 ab will cover all of it. A
smaller portion of the leptoquark parameter space is covered by future
colliders: for example, in a di-leptoquark search, a 100 TeV 10
ab collider has a projected sensitivity up to leptoquark masses of 12
TeV (extendable to 21 TeV with a strong coupling for single leptoquark
production), whereas leptoquark masses up to 41 TeV may in principle explain
the anomalies.Comment: 24 pages, 10 figures. v2: Improved discussion and references added,
version submitted to JHE
Primal robustness and semidefinite cones
This paper reformulates and streamlines the core tools of robust stability
and performance for LTI systems using now-standard methods in convex
optimization. In particular, robustness analysis can be formulated directly as
a primal convex (semidefinite program or SDP) optimization problem using sets
of gramians whose closure is a semidefinite cone. This allows various
constraints such as structured uncertainty to be included directly, and
worst-case disturbances and perturbations constructed directly from the primal
variables. Well known results such as the KYP lemma and various scaled small
gain tests can also be obtained directly through standard SDP duality. To
readers familiar with robustness and SDPs, the framework should appear obvious,
if only in retrospect. But this is also part of its appeal and should enhance
pedagogy, and we hope suggest new research. There is a key lemma proving
closure of a grammian that is also obvious but our current proof appears
unnecessarily cumbersome, and a final aim of this paper is to enlist the help
of experts in robust control and convex optimization in finding simpler
alternatives.Comment: A shorter version submitted to CDC 1
Household Food Expenditures, Parental Time Allocation, and Childhood Obesity
The increased prevalence of childhood obesity is a major concern for society. This study aims at exploring the influence of the parents (especially parental time allocation choices) on childrens obesity-related health outcomes and examining the potential differences between the fathers and the mothers marginal effects. A household with two parents and one child is modeled. The household production theory and the collective household modeling structure are combined. The model treats the mother, the father and the child as three separate agents with individual preferences. The two parents interaction is modeled within the collective model framework by assuming that they will reach Pareto efficient resource allocation between them. In order to capture the dynamics between parents and the child, parents-child interaction is modeled in a two-stage Stackleberg game structure where the child is allowed to have certain decision choices of his/her own. This game structure allows us to explore the parental influence on the childs health outcomes while allowing the child to have influencing power in the household decision-making process. Based on this theoretical model, a general triangular system with one childs health production equation and five health inputs demand equations is derived and estimated. The empirical estimation is performed for three systems: pooled model, the younger children model (of age 9 to 11), and the older children model (of age 13 to 15). The empirical results shows positive relationship between total household monthly food expenditure and the childs BMI outcome. Both parents time spent with the child are important and both show negatively significant impact on the childs BMI outcomes in all models and the pool model confirms the statistical difference between paternal and maternal time spent with the child. Other mother-related variables show more influence on the childrens BMI. There exists a complementary relationship between mothers income and fathers time allocation. Fathers have more significant influence on household food expenditure compared to mothers. In general, mothers show more significant influence on the parental time allocation compared to fathers. The main contribution of this study is that it develops a general theoretical framework to capture the dynamics in parents-child interaction. Based on this theoretical model, empirical analysis and future work can be conducted in a theoretically consistent way.Food Consumption/Nutrition/Food Safety, Health Economics and Policy,
Large enhancement of the effective second-order nonlinearity in graphene metasurfaces
Using a powerful homogenization technique, one- and two-dimensional graphene
metasurfaces are homogenized both at the fundamental frequency (FF) and second
harmonic (SH). In both cases, there is excellent agreement between the
predictions of the homogenization method and those based on rigorous numerical
solutions of Maxwell equations. The homogenization technique is then employed
to demonstrate that, owing to a double-resonant plasmon excitation mechanism
that leads to strong, simultaneous field enhancement at the FF and SH, the
effective second-order susceptibility of graphene metasurfaces can be enhanced
by more than three orders of magnitude as compared to the intrinsic
second-order susceptibility of a graphene sheet placed on the same substrate.
In addition, we explore the implications of our results on the development of
new active nanodevices that incorporate nanopatterned graphene structures.Comment: 11 pages, 12 figure
Testing non-nested structural equation models
In this paper, we apply Vuong's (1989) likelihood ratio tests of non-nested
models to the comparison of non-nested structural equation models. Similar
tests have been previously applied in SEM contexts (especially to mixture
models), though the non-standard output required to conduct the tests has
limited their previous use and study. We review the theory underlying the tests
and show how they can be used to construct interval estimates for differences
in non-nested information criteria. Through both simulation and application, we
then study the tests' performance in non-mixture SEMs and describe their
general implementation via free R packages. The tests offer researchers a
useful tool for non-nested SEM comparison, with barriers to test implementation
now removed.Comment: 24 pages, 6 figure
- …