114,741 research outputs found
Multiparticle interference in electronic Mach-Zehnder interferometers
We study theoretically electronic Mach-Zehnder interferometers built from
integer quantum Hall edge states, showing that the results of recent
experiments can be understood in terms of multiparticle interference effects.
These experiments probe the visibility of Aharonov-Bohm (AB) oscillations in
differential conductance as an interferometer is driven out of equilibrium by
an applied bias, finding a lobe pattern in visibility as a function of voltage.
We calculate the dependence on voltage of the visibility and the phase of AB
oscillations at zero temperature, taking into account long range interactions
between electrons in the same edge for interferometers operating at a filling
fraction . We obtain an exact solution via bosonization for models in
which electrons interact only when they are inside the interferometer. This
solution is non-perturbative in the tunneling probabilities at quantum point
contacts. The results match observations in considerable detail provided the
transparency of the incoming contact is close to one-half: the variation in
visibility with bias voltage consists of a series of lobes of decreasing
amplitude, and the phase of the AB-fringes is practically constant inside the
lobes but jumps by at the minima of the visibility. We discuss in
addition the consequences of approximations made in other recent treatments of
this problem. We also formulate perturbation theory in the interaction strength
and use this to study the importance of interactions that are not internal to
the interferometer.Comment: 20 pages, 15 figures, final version as publishe
Interpreting mass measurements in the SMEFT
Measurements of the mass () provide an important consistency
check of the Standard Model (SM) and constrain the possibility of physics
beyond the SM. Precision measurements of at hadron colliders are inferred
from kinematic distributions of transverse variables. We examine how this
inference is modified when considering the presence of physics beyond the SM
expressed in terms of local contact operators. We show that Tevatron
measurements of using transverse variables are transparent and applicable
as consistent constraints in the Standard Model Effective Field Theory (SMEFT)
with small measurement bias. This means that the leading challenge to
interpreting these measurements in the SMEFT is the pure theoretical
uncertainty in how these measurements are mapped to Lagrangian parameters. We
stress the need to avoid using naive combinations of Tevatron and LEPII
measurements of without the introduction of any SMEFT theoretical error
to avoid implicit UV assumptions. In a companion paper, we implement our
procedure to consistently incorporate measurements into a global fit.Comment: 6pp, 4 figures V2: minor typo corrections and text clarifications,
matches journal versio
Beyond LIMD bias: a measurement of the complete set of third-order halo bias parameters
We present direct measurements of cubic bias parameters of dark matter halos
from the halo-matter-matter-matter trispectrum. We measure this statistic
efficiently by cross-correlating the halo field measured in N-body simulations
with specific third-order nonlocal transformations of the initial density field
in the same simulation. Together with the recent Abidi & Baldauf (2018), these
are the first measurements of halo bias using the four-point function that have
been reported to date. We also obtain constraints on the quadratic bias
parameters. For all individual cubic parameters involving the tidal field
, we find broad consistency with the prediction of the
Lagrangian local-in-matter-density ansatz, with some indications of a positive
Lagrangian coefficient multiplying the time derivative of
. For the quadratic tidal bias (), we obtain a
significant detection of a negative Lagrangian tidal bias.Comment: 29 pages, 12 figures; v2: new renormalization procedure, added figure
12, results at higher redshifts on figs 1-5, added appendix B, C and F,
clarifications throughout; v3: clarifications throughout, version accepted by
JCA
Flow equations for Hamiltonians: Contrasting different approaches by using a numerically solvable model
To contrast different generators for flow equations for Hamiltonians and to
discuss the dependence of physical quantities on unitarily equivalent, but
effectively different initial Hamiltonians, a numerically solvable model is
considered which is structurally similar to impurity models. By this we discuss
the question of optimization for the first time. A general truncation scheme is
established that produces good results for the Hamiltonian flow as well as for
the operator flow. Nevertheless, it is also pointed out that a systematic and
feasible scheme for the operator flow on the operator level is missing. For
this, an explicit analysis of the operator flow is given for the first time. We
observe that truncation of the series of the observable flow after the linear
or bilinear terms does not yield satisfactory results for the entire parameter
regime as - especially close to resonances - even high orders of the exact
series expansion carry considerable weight.Comment: 25 pages, 10 figure
Modeling Biased Tracers at the Field Level
In this paper we test the perturbative halo bias model at the field level.
The advantage of this approach is that any analysis can be done without sample
variance if the same initial conditions are used in simulations and
perturbation theory calculations. We write the bias expansion in terms of
modified bias operators in Eulerian space, designed such that the large bulk
flows are automatically resummed and not treated perturbatively. Using these
operators, the bias model accurately matches the Eulerian density of halos in
N-body simulations. The mean-square model error is close to the Poisson shot
noise for a wide range of halo masses and it is rather scale-independent, with
scale-dependent corrections becoming relevant at the nonlinear scale. In
contrast, for linear bias the mean-square model error can be higher than the
Poisson prediction by factors of up to a few on large scales, and it becomes
scale dependent already in the linear regime. We show that by weighting
simulated halos by their mass, the mean-square error of the model can be
further reduced by up to an order of magnitude, or by a factor of two when
including mass scatter. We also test the Standard Eulerian bias model
using the nonlinear matter field measured from simulations and show that it
leads to a larger and more scale-dependent model error than the bias expansion
based on perturbation theory. These results may be of particular relevance for
cosmological inference methods that use a likelihood of the biased tracer at
the field level, or for initial condition and BAO reconstruction that requires
a precise estimate of the large-scale potential from the biased tracer density.Comment: 61 pages, 27 figures. Minor edits and added references to match
published versio
Measuring Which-Path Information with Coupled Electronic Mach-Zehnder Interferometers
We theoretically investigate a generalized "which-path" measurement on an
electronic Mach-Zehnder Interferometer (MZI) implemented via Coulomb coupling
to a second electronic MZI acting as a detector. The use of contextual values,
or generalized eigenvalues, enables the precise construction of which-path
operator averages that are valid for any measurement strength from the
available drain currents. The form of the contextual values provides direct
physical insight about the measurement being performed, providing information
about the correlation strength between system and detector, the measurement
inefficiency, and the proper background removal. We find that the detector
interferometer must display maximal wave-like behavior to optimally measure the
particle-like which-path information in the system interferometer,
demonstrating wave-particle complementarity between the system and detector. We
also find that the degree of quantum erasure that can be achieved by
conditioning on a specific detector drain is directly related to the ambiguity
of the measurement. Finally, conditioning the which-path averages on a
particular system drain using the zero frequency cross-correlations produces
conditioned averages that can become anomalously large due to quantum
interference; the weak coupling limit of these conditioned averages can produce
both weak values and detector-dependent semi-weak values.Comment: 17 pages, 12 figures, published version including appendi
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