3,152 research outputs found
Form-factors computation of Friedel oscillations in Luttinger liquids
We show how to analytically determine for the "Friedel
oscillations" of charge density by a single impurity in a 1D Luttinger liquid
of spinless electrons.Comment: Revtex, epsf, 4pgs, 2fig
Kink-boundary collisions in a two dimensional scalar field theory
In a two-dimensional toy model, motivated from five-dimensional heterotic
M-theory, we study the collision of scalar field kinks with boundaries. By
numerical simulation of the full two-dimensional theory, we find that the kink
is always inelastically reflected with a model-independent fraction of its
kinetic energy converted into radiation. We show that the reflection can be
analytically understood as a fluctuation around the scalar field vacuum. This
picture suggests the possibility of spontaneous emission of kinks from the
boundary due to small perturbations in the bulk. We verify this picture
numerically by showing that the radiation emitted from the collision of an
initial single kink eventually leads to a bulk populated by many kinks.
Consequently, processes changing the boundary charges are practically
unavoidable in this system. We speculate that the system has a universal final
state consisting of a stack of kinks, their number being determined by the
initial energy
Gravitational waves from fundamental axion dynamics
A totally asymptotically free QCD axion model, where all couplings flow to zero in the infinite energy limit, was recently formulated. A very interesting feature of this fundamental theory is the ability to predict some low-energy observables, like the masses of the extra fermions and scalars. Here we find and investigate a region of the parameter space where the Peccei-Quinn (PQ) symmetry is broken quantum mechanically through the Coleman-Weinberg mechanism. This results in an even more predictive framework: the axion sector features only two independent parameters (the PQ symmetry breaking scale and the QCD gauge coupling). In particular, we show that the PQ phase transition is strongly first order and can produce gravitational waves within the reach of future detectors. The predictivity of the model leads to a rigid dependence of the phase transition (like its duration and the nucleation temperature) and the gravitational wave spectrum on the PQ symmetry breaking scale and the QCD gauge coupling
Beyond Chili Peppers: Using Custom Surveys to Improve Learning and Assessment
This article shows how customized learning surveys can be used to capture students’ perceptions of their learning in ways that aid pedagogy and students’ growth. In contrast to relying solely on standardized university-designed evaluations of teaching, thoughtful use of self-designed surveys about learning offers four benefits. First, this technique generates timely feedback in a way that allows instructors to adjust our teaching when it matters most. Second, custom surveys allow instructors to center learning as the core outcome and therefore facilitate specific, educationally relevant, and useful feedback. Third, the approach can cue students to think of themselves as the core agent of their own education, which helps them move toward greater self-directed learning in the long term. Finally, the approach facilitates the collection of data that can be used in annual assessments or applications for tenure and promotion, which will be increasingly important as more universities seek alternatives to using standardized student evaluations in personnel decisions. In this article I lay out my rationale for adopting this method, describe how it works, and explain why I see it as fruitful for improving assessment, teaching, and learning
Boundary bound states and boundary bootstrap in the sine-Gordon model with Dirichlet boundary conditions.
We present a complete study of boundary bound states and related boundary
S-matrices for the sine-Gordon model with Dirichlet boundary conditions. Our
approach is based partly on the bootstrap procedure, and partly on the explicit
solution of the inhomogeneous XXZ model with boundary magnetic field and of the
boundary Thirring model. We identify boundary bound states with new ``boundary
strings'' in the Bethe ansatz. The boundary energy is also computed.Comment: 25 pages, harvmac macros Report USC-95-001
Direct Calculation of Breather S Matrices
We formulate a systematic Bethe-Ansatz approach for computing bound-state
(``breather'') S matrices for integrable quantum spin chains. We use this
approach to calculate the breather boundary S matrix for the open XXZ spin
chain with diagonal boundary fields. We also compute the soliton boundary S
matrix in the critical regime.Comment: 23 pages, LaTeX, 1 eps figur
Gauge Invariant Action for the Open Bosonic String: Tachyon Action
A gauge invariant action for the open bosonic string has been proposed in an
earlier paper. We work out the consequences of this proposal for the lowest
mode, viz. the tachyon. The action can be calculated for generic momenta,
perturbatively, order by order in the tachyon field. For on shell tachyons we
explicitly calculate the cubic action and show that it reproduces the correct
equations of motion and coincides wih the function to the required
order. The calculation is done in terms of bare fields with a finite cutoff,
which is the original prescription. We also show that it is possible in some
momentum regions to renormalize the theory and eliminate the cutoff dependence
so that the continuum limit can be taken. After renormalization, the parameter
is replaced by where is an IR cutoff, is the UV
cutoff and is some renormalization scale. There is also some arbitrariness
in the overall normalization due to the choice of regularization scheme - this
does not affect on-shell quantities. We also rederive within this scheme, the
action in the region of zero momentum, which gives the exact (tree level)
tachyon potential. The tachyon potential is consistent with Sen's conjecture
that the height of the potential is the same as the tension of the brane.Comment: 31 pages, Late
Exact noncommutative solitons in p-adic strings and BSFT
The tachyon field of p-adic string theory is made noncommutative by replacing
ordinary products with noncommutative products in its exact effective action.
The same is done for the boundary string field theory, treated as the p -> 1
limit of the p-adic string. Solitonic lumps corresponding to D-branes are
obtained for all values of the noncommutative parameter theta. This is in
contrast to usual scalar field theories in which the noncommutative solitons do
not persist below a critical value of theta. As theta varies from zero to
infinity, the solution interpolates smoothly between the soliton of the p-adic
theory (respectively BSFT) to the noncommutative soliton.Comment: 1+14 pages (harvmac b), 1 eps figure, v2: references added, typos
correcte
Toda Lattice Models with Boundary
We consider the soliton solutions in 1- and (1+1)-dimensional Toda lattice
models with a boundary. We make use of the solutions already known on a full
line by means of the Hirota's method. We explicitly construct the solutions
satisfying the boundary conditions. The -symmetric boundary
condition can be introduced by the two-soliton solutions naturally.Comment: 9 pages, latex, no figure
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