913 research outputs found
Quantum Cramer-Rao bound for a Massless Scalar Field in de Sitter Space
How precisely can we estimate cosmological parameters by performing a quantum
measurement on a cosmological quantum state? In quantum estimation theory the
variance of an unbiased parameter estimator is bounded from below by the
inverse of measurement-dependent Fisher information and ultimately by quantum
Fisher information, which is the maximization of the former over all positive
operator valued measurements. Such bound is known as the quantum Cramer-Rao
bound. We consider the evolution of a massless scalar field with Bunch-Davies
vacuum in a spatially flat FLRW spacetime, which results in a two-mode squeezed
vacuum out-state for each field wave number mode. We obtain the expressions of
the quantum Fisher information as well as the Fisher informations associated to
occupation number measurement and power spectrum measurement, and show the
specific results of their evoluation for pure de Sitter expansion and de Sitter
expansion followed by a radiation-dominated phase as examples. We will discuss
these results from the point of view of the quantum-to-classical transition of
cosmological perturbations and show quantitatively how this transition and the
residual quantum correlations affect the bound on the precision.Comment: 16 pages, published versio
The decoherence and interference of cosmological arrows of time for a de Sitter universe with quantum fluctuations
We consider the superposition of two semiclassical solutions of the
Wheeler-DeWitt equation for a de Sitter universe, describing a quantized scalar
vacuum propagating in a universe that is contracting in one case and expanding
in the other, each identifying a opposite cosmological arrow of time. We
discuss the suppression of the interference terms between the two arrows of
time due to environment-induced decoherence caused by modes of the scalar
vacuum crossing the Hubble horizon. Furthermore, we quantify the effect of the
interference on the expectation value of the observable field mode
correlations, with respect to an observer that we identify with the spatial
geometry
A Wheeler-DeWitt Equation with Time
The equation for canonical gravity produced by Wheeler and DeWitt in the late
1960s still presents difficulties both in terms of its mathematical solution
and its physical interpretation. One of these issues is, notoriously, the
absence of an explicit time. In this short note, we suggest one simple and
straightforward way to avoid this occurrence. We go back to the classical
equation that inspired Wheeler and DeWitt (namely, the
Hamilton--Jacobi--Einstein equation) and make explicit, before quantization,
the presence of a known, classically meaningful notion of time. We do this by
allowing Hamilton's principal function to be explicitly dependent on this time
locally. This choice results in a Wheeler--DeWitt equation with time. A working
solution for the de Sitter minisuperspace is shown
Impacts of radiative corrections on measurements of lepton flavour universality in decays
Radiative corrections to decays may have an impact
on predictions and measurements of the lepton flavour universality observables
and . In this paper, a comparison between
recent calculations of the effect of soft-photon corrections on
and , and corrections generated by the
widely used package PHOTOS is given. The impact of long-distance Coulomb
interactions, which are not simulated in PHOTOS, is discussed. Furthermore, the
effect of high-energy photon emission is studied through pseudo-experiments in
an LHCb-like environment. It is found that over- or underestimating these
emissions can cause a bias on as high as 7%. However, this
bias depends on individual analyses, and future high precision measurements
require an accurate evaluation of these QED corrections.Comment: 8 pages, 21 figures, published by EPJ
Clock Time in Quantum Cosmology
We consider the conditioning of the timeless solution to the Wheeler-DeWitt
equation by a predefined matter clock state in the simple scenario of de Sitter
universe. The resulting evolution of the geometrodynamical degree of freedom
with respect to clock time is characterized by the "Berry connection" of the
reduced geometrodynamical space, which relies on the coupling of the clock with
the geometry. When the connection vanishes, the standard Schr\"odinger equation
is obtained for the geometry with respect to clock time. When one considers
environment-induced decoherence in the semi-classical limit, this condition is
satisfied and clock time coincides with cosmic time. Explicit results for the
conditioned wave functions for minimal clocks made up of two quantum harmonic
oscillator eigen-states are shown
Determination of the Cabibbo-Kobayashi-Maskawa matrix element
In this review we present and discuss the determination of the magnitude of
the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameter . The CKM matrix
parametrizes the weak charged current interactions of quarks in the Standard
Model (SM), and a precise determination of its elements has always been one of
the most important targets of particle physics. The precise knowledge of the
value plays a pivotal role in testing the flavour sector of the SM
and in the analyses of the unitarity of the CKM matrix. The SM does not predict
the values of the CKM matrix elements, which have to be extracted by
experimental data. Given the variety of channels that allow the extraction of
, different theoretical and experimental techniques are mustered for
the determination. The exertion toward precision represents not only
a significant test of our theoretical procedures but a stimulus towards better
detection performances. The most precise measurements of come from
semileptonic decays, that being tree level at the lowest order in the SM are
generally considered unaffected by physics beyond the SM.
After summarizing the characteristics of the SM that set the frame for the
determination of , we discuss inclusive and exclusive semileptonic
decays. We analyze the extraction methods and recent results,
detailing both the theoretical and experimental techniques, and, finally,
outline future prospects. We also comment on exclusive decays into heavy
leptons, on the observables and , on decays to excited
meson states and on baryon decays.Comment: Completely revised and updated: latest results (including baryons),
details, tables, figures and references added; 77 pages, 19 figures (invited
review on J. Phys. G: Nucl. Part. Phys
Testing lepton flavour universality in semileptonic decays
Lepton Flavour Universality tests with semileptonic
decays are important to corroborate the present anomalies in the similar ratios
, and can provide complementary constraints on possible origins of
these anomalies beyond the Standard Model. In this paper we provide - for the
first time - all the necessary theoretical ingredients to perform and interpret
measurements of at the LHCb experiment. For this, we revisit
the heavy-quark expansion of the relevant hadronic matrix elements, and provide
their expressions to order and accuracy. Moreover, we study
the sensitivity to the form factor parameters given the projected size and
purity of upcoming and future LHCb datasets of decays. We demonstrate explicitly the need to perform
a simultaneous fit to both final states. Finally, we provide
projections for the uncertainty of based on the form factor
analysis from semimuonic decays and theoretical relations based on the
heavy-quark expansion.Comment: 27 pages, 6 figures. v2: Fixed error in subleading IW function, added
supplementary information; conclusions unchange
Thermodynamic Reverse Bounds for General Open Quantum Processes
Various quantum thermodynamic bounds are shown to stem from a single tighter
and more general inequality, consequence of the operator concavity of the
logarithmic function. Such an inequality, which we call the "thermodynamic
reverse bound", is compactly expressed as a quantum relative entropy, from
which it inherits mathematical properties and meaning. As concrete examples, we
apply our bound to evaluate the thermodynamic length for open processes, the
heat exchange in erasure processes, and the maximal energy outflow in general
quantum evolutions.Comment: v2: added six colorful plots for the heat exchanged in erasure
processes, accepted in PRA; v1: 6 pages, two-colum
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