6,699 research outputs found
Aging dynamics in quenched noisy long-range quantum Ising models
We consider the -dimensional transverse-field Ising model with power-law
interactions in the presence of a noisy longitudinal field
with zero average. We study the longitudinal-magnetization dynamics of an
initial paramagnetic state after a sudden switch-on of both the interactions
and the noisy field. While the system eventually relaxes to an
infinite-temperature state with vanishing magnetization correlations, we find
that two-time correlation functions show aging at intermediate times. Moreover,
for times shorter than the inverse noise strength and distances longer
than with being the lattice spacing, we find a
critical scaling regime of correlation and response functions consistent with
the model A dynamical universality class with an initial-slip exponent
and dynamical critical exponent . We obtain our results
analytically by deriving an effective action for the magnetization field
including the noise in a non-perturbative way. The above scaling regime is
governed by a non-equilibrium fixed point dominated by the noise fluctuations.Comment: Accepted version, 11 pages, 5 figure
Scalar-tensor theories, trace anomalies and the QCD-frame
We consider the quantum effects of matter fields in scalar-tensor theories
and clarify the role of trace anomaly when switching between conformally
related `frames'. We exploit the property that the couplings between the scalar
and the gauge fields are not frame-invariant in order to define a `QCD-frame',
where the scalar is not coupled to the gluons. We show that this frame is a
natural generalization of the `Jordan frame' in the case of non-metric theories
and that it is particularly convenient for gravitational phenomenology: test
bodies have trajectories that are as close as possible to geodesics with
respect to such a metric and equivalence principle violations are directly
proportional to the scalar coupling parameters written in this frame. We show
how RG flow and decoupling work in metric and non-metric theories. RG-running
commutes with the operation of switching between frames at different scales.
When only matter loops are considered, our analysis confirms that metricity is
stable under radiative corrections and shows that approximate metricity is
natural in a technical sense.Comment: 10 pages. Minor changes to the main text, appendix added. To appear
on PR
An integrated approach project for the revaluation of a traditional sourdough bread production chain
The influence of organic and conventional farming systems on the performance of a panel of old and modern Italian bread wheat varieties has been evaluated, with the aim to individuate an agronomic protocol suitable for the production of a sourdough bread traditionally prepared in a hill zone of Emilia-Romagna. The agronomic and technological characterisation of the wheat samples obtained in organic and conventional farming conditions has been done and the sensorial qualities of the sourdough bread obtained have been evaluated
Improved local-constant-field approximation for strong-field QED codes
The local-constant-field approximation (LCFA) is an essential theoretical
tool for investigating strong-field QED phenomena in background electromagnetic
fields with complex spacetime structure. In our previous work
[Phys.~Rev.~A~\textbf{98}, 012134 (2018)] we have analyzed the shortcomings of
the LCFA in nonlinear Compton scattering at low emitted photon energies for the
case of a background plane-wave field. Here, we generalize that analysis to
background fields, which can feature a virtually arbitrary spacetime structure.
In addition, we provide an explicit and simple implementation of an improved
expression of the nonlinear Compton scattering differential probability that
solves the main shortcomings of the standard LCFA in the infrared region, and
is suitable for background electromagnetic fields with arbitrary spacetime
structure such as those occurring in particle-in-cell simulations. Finally, we
carry out a systematic procedure to calculate the probability of nonlinear
Compton scattering per unit of emitted photon light-cone energy and of
nonlinear Breit-Wheeler pair production per unit of produced positron
light-cone energy beyond the LCFA in a plane-wave background field, which
allows us to identify the limits of validity of this approximation
quantitatively.Comment: 15 pages, 3 figure
Study of symmetry in F(R) theory of gravity
An action in which the Ricci scalar is nonminimally coupled with a scalar
field and contains higher order curvature invariant terms carries a conserved
current under certain conditions that decouples geometric part from the scalar
field. The conserved current relates the pair of arbitrary coupling parameters
and with the gravitational field variable, where
is the Brans-Dicke coupling parameter. The existence of such
conserved current may be helpful to sketch the cosmological evolution from its
early age till date in a single frame.Comment: 6 page
Implementing nonlinear Compton scattering beyond the local constant field approximation
In the calculation of probabilities of physical processes occurring in a
background classical field, the local constant field approximation (LCFA)
relies on the possibility of neglecting the space-time variation of the
external field within the region of formation of the process. This
approximation is widely employed in strong-field QED as it allows to evaluate
probabilities of processes occurring in arbitrary electromagnetic fields
starting from the corresponding quantities computed in a constant
electromagnetic field. Here, we demonstrate in the case of nonlinear single
Compton scattering that the LCFA is quantitatively and qualitatively
insufficient for describing the low-energy part of the emitted photon
probability. In addition, we provide a simple recipe to implement an improved
expression of the photon emission probability beyond the LCFA in numerical
codes, which are an essential tool to interpret present and upcoming
experiments in strong-field QED.Comment: 12 pages, 3 figur
Catching the Gazelle: Antecedents and Outcomes of High Growth Firms
This three-essay dissertation seeks to resolve some of the unanswered questions that exist about high-growth firms (HGFs). Paper I identifies the antecedents and outcomes of HGFs to better inform economic development policy. In explaining the theoretical and operational constructs of these concepts, a model of the situation of high-growth firms is developed, dubbed the Model of High Growth Firm Antecedents and Outputs. Antecedents to HGFs include an entrepreneurial mindset, firm strategic resources, and firm structural characteristics, while outputs of HGFs include regional innovation outcomes and regional economic outcomes. Paper II investigated the quantitative association between antecedents and outputs of HGFs. This paper used path analysis to test hypotheses within the Regional High-Growth Firm Antecedents and Outcomes Framework, and finds a strong positive association between most antecedents (human capital, startup capital, and business costs) and HGFs, a positive relationship between most antecedents and outcomes (employment and per capita income), and an association between HGFs and employment. Paper III establishes a typology of HGFs using cluster-discriminate analysis. Using a sample of 26,104 firms in the state of Ohio from the Quarterly Census of Employment and Wages, this paper finds that only a small portion of HGFs display high-growth characteristics described in the literature
- …