373 research outputs found
Aspects of Track-Assisted Mass
Track-assisted mass is a proxy for jet mass that only uses direction
information from charged particles, allowing it to be measured at the Large
Hadron Collider with very fine angular resolution. In this paper, we introduce
a generalization of track-assisted mass and analyze its performance in both
parton shower generators and resummed calculations. For the original
track-assisted mass, the track-only mass is rescaled by the charged energy
fraction of the jet. In our generalization, the rescaling factor includes both
per-jet and ensemble-averaged information, facilitating a closer correspondence
to ordinary jet mass. Using the track function formalism in electron-positron
collisions, we calculate the spectrum of generalized track-assisted mass to
next-to-leading-logarithmic order with leading-order matching. These resummed
calculations provide theoretical insight into the close correspondence between
track-assisted mass and ordinary jet mass. With the growing importance of jet
grooming algorithms, we also calculate track-assisted mass on soft-drop groomed
jets.Comment: 35+17 pages, 22 figures; v3: improvements to calculation and
presentation to appear in JHE
Theoretical And Phenomenological Viability Of Scalar Field Theories
The objective of this Thesis is to explore several related questions with regards to criteria for viability in scalar field theories. Roughly the first half is devoted to theoretical criteria, while the second half focuses on phenomenological ones. We begin with an overview of theories that violate the null energy condition, highlighting the pathologies that inevitably appear. We then present a theory that violates the null energy condition while remaining free of the problems that plagued previous attempts. Next we explore a global condition for classical stability in scalar field theories, namely, the requirement that the total energy of the space-time be positive. This property is guaranteed if the theory admits a positive energy theorem. After reviewing existing proofs of positive energy for canonical scalar fields, we then extend those proofs to theories with derivative interactions, proving a positive energy theorem for a wide class of P(X) theories. The second half of this Thesis considers experimental constraints on scalar field theories. We focus on what may be learned from atom interferometry experiments, which have been a powerful probe of fundamental physics for over two decades but only recently gained the ability to constrain screened scalar field theories. We present a general analytic and numerical framework for precise predictions of scalar field theories in atom interferometry experiments, and use those techniques to derive new limits on chameleon and symmetron field theories
Mapping the Weak-Field Limit of Scalar-Gauss-Bonnet Gravity
We derive the weak field limit of scalar-Gauss-Bonnet theory and place novel
bounds on the parameter space using terrestrial and space-based experiments. In
order to analyze the theory in the context of a wide range of experiments, we
compute the deviations from Einstein gravity around source masses with planar,
cylindrical, and spherical symmetry. We find a correction to the Newtonian
potential around spherical and cylindrical sources that can be larger than PPN
corrections sufficiently close to the source. We use this to improve on
laboratory constraints on the scalar-Gauss-Bonnet coupling parameter
by two orders of magnitude. Present laboratory and Solar System bounds reported
here are superseded by tests deriving from black holes.Comment: 18 page
Generalized Fragmentation Functions for Fractal Jet Observables
We introduce a broad class of fractal jet observables that recursively probe
the collective properties of hadrons produced in jet fragmentation. To describe
these collinear-unsafe observables, we generalize the formalism of
fragmentation functions, which are important objects in QCD for calculating
cross sections involving identified final-state hadrons. Fragmentation
functions are fundamentally nonperturbative, but have a calculable
renormalization group evolution. Unlike ordinary fragmentation functions,
generalized fragmentation functions exhibit nonlinear evolution, since fractal
observables involve correlated subsets of hadrons within a jet. Some special
cases of generalized fragmentation functions are reviewed, including jet charge
and track functions. We then consider fractal jet observables that are based on
hierarchical clustering trees, where the nonlinear evolution equations also
exhibit tree-like structure at leading order. We develop a numeric code for
performing this evolution and study its phenomenological implications. As an
application, we present examples of fractal jet observables that are useful in
discriminating quark jets from gluon jets.Comment: 37+18 pages, 24 figure
Optimizing a scaffoldless approach for cartilage tissue engineering
Articular cartilage has a poor intrinsic healing response, so tissue engineering provides a promising approach for cartilage regeneration. The major objective of this proposal was to enhance the self-assembling process, used in articular cartilage tissue engineering, by investigating the effects of construct confinement, hydrostatic pressure application, and growth factor addition. First, the effects of construct confinement in different directions and at different times were investigated. It was demonstrated that construct confinement resulted in enhanced biomechanical properties in the direction orthogonal to the confinement surface, either by enhancing collagen organization or by increasing collagen production. Next, the effects of hydrostatic pressure at different timepoints, magnitudes, and frequencies on the biomechanical and biochemical properties of self-assembled constructs were determined. It was demonstrated that the application of static hydrostatic pressure, at 10 MPa, for 1 h/day, from days 10-14 days led to significant increases in compressive and tensile properties, accompanied by significant increases in GAG and collagen content, respectively. To our knowledge, this was the first study to demonstrate increases in the biomechanical properties of tissue from pure HP application. Furthermore, the effects of exogenous application of growth factors, at varying concentrations, dosages, and combinations, with and without hydrostatic pressure, were assessed on the biochemical and biomechanical properties of engineered constructs. A systematic approach was used to determine the effects of BMP-2, IGF-I, and TGF-beta1, alone and in combination, on the functional properties of engineered constructs. This was the first study to demonstrate significant increases in both compressive and tensile biomechanical properties as a result of growth factor treatment. Also, for the first time, synergistic and additive effects on construct biomechanical and biochemical properties were found when combining growth factor treatment with hydrostatic pressure application. Finally, the effects of various decellularization treatments were examined, and it was determined that it was possible to remove cells while maintaining construct functional properties. The results presented in this thesis are exciting, as they have allowed for a better understanding of the self-assembling process, and have allowed the self-assembled constructs to mature into functional articular cartilage, as evidenced by biomechanical and biochemical properties spanning native tissue values
2-manifold recognition is in logspace
We prove that the homeomorphism problem for 2 manifolds can be decided in logspace. The proof relies on Reingold's logspace solution to the undirected s, t-connectivity problem in graphs
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