3,499 research outputs found
Higgs-Dilaton Lagrangian from Spectral Regularization
In this letter we calculate the full Higgs-Dilaton action describing the Weyl
anomaly using the bosonic spectral action. This completes the work we started
in our previous paper (JHEP 1110 (2011) 001). We also clarify some issues
related to the dilaton and its role as collective modes of fermions under
bosonization
Coherent instabilities of intense high-energy "white" charged-particle beams in the presence of nonlocal effects within the context of the Madelung fluid description
A hydrodynamical description of coherent instabilities that take place in the
longitudinal dynamics of a charged-particle coasting beam in a high-energy
accelerating machine is presented. This is done in the framework of the
Madelung fluid picture provided by the Thermal Wave Model. The well known
coherent instability charts in the complex plane of the longitudinal coupling
impedance for monochromatic beams are recovered. The results are also
interpreted in terms of the deterministic approach to modulational instability
analysis usually given for monochromatic large amplitude wave train propagation
governed by the nonlinear Schr\"odinger equation. The instability analysis is
then extended to a non-monochromatic coasting beam with a given thermal
equilibrium distribution, thought as a statistical ensemble of monochromatic
incoherent coasting beams ("white" beam). In this hydrodynamical framework, the
phenomenon of Landau damping is predicted without using any kinetic equation
governing the phase space evolution of the system.Comment: 14 pages, 1 figur
Comparison of Secondhand Smoke Exposure in Minority and Non-minority Children with Asthma
ObjectiveâDetermine if secondhand smoke exposure (SHSE) is related to asthma-related functional morbidity by examining racial/ethnic differences in Non-Latino White (NLW), African American, and Latino families and whether racial/ethnic SHSE differences across families persist when accounting for smoking factors.
MethodsâParticipants were 305 caregiver smokers of children with asthma. Two passive dosimeters measured SHS: one in the home and one worn by the child.
ResultsâHigher SHSE was related to greater asthma-related functional morbidity. African Americans had higher levels of home SHSE than Latinos (p = .003) or NLWs (p = .021). SHSE as assessed by the child worn dosimeter did not differ across race/ethnicity. African American families were less likely to report a household smoking ban (46.4%) compared to Latinos (79.2%) and NLWs (67.9%; p \u3c .05). African Americans were less likely to report having two or more smokers in the home (37.2%) compared to NLWs (53.6%; p \u3c .05). NLWs reported the highest number of cigarettes smoked daily (Mdn = 15.00) compared to Latinos (Mdn = 10.00; p = .001) and African Americans (Mdn = 10.00; p \u3c .001). SHS home exposure levels were regressed on race/ethnicity and relevant covariates. Household smoking ban (p \u3c .001) and only one smoker in the home (p = .005) were associated with lower levels of SHS in the home; race/ethnicity was not significant.
ConclusionsâDifferences in SHSE across race/ethnicity exist among children with asthma, possibly due to differential presence of a household smoking ban and number of smokers in the home
Dynamics of the wakefield of a multi-petawatt, femtosecond laser pulse in a configuration with ultrarelativistic electrons
The wake field excitation in an unmagnetized plasma by a multi-petawatt,
femtosecond, pancake-shaped laser pulse is described both analytically and
numerically in the regime with ultrarelativistic electron jitter velocities,
when the plasma electrons are almost expelled from the pulse region. This is
done, for the first time, in fluid theory. A novel mathematical model is
devised that does not break down for very intense pump strengths, in contrast
to the standard approach that uses the laser field envelope and the
ponderomotive guiding center averaging. This is accomplished by employing a
three-timescale description, with the intermediate scale associated with the
nonlinear phase of the electromagnetic wave and with the bending of its wave
front. The evolution of the pulse and of its electrostatic wake are studied by
the numerical solution in a two-dimensional geometry, with the spot diameter
\geq 100 microns. It reveals that the optimum initial pulse length needs to be
somewhat bigger than 1 micron (1-2 oscillations), as suggested by simple
analytical local estimates, because the nonlocal plasma response tends to
stretch very short pulses
High energy bosons do not propagate
We discuss the propagation of bosons (scalars, gauge fields and gravitons) at
high energy in the context of the spectral action. Using heat kernel
techniques, we find that in the high-momentum limit the quadratic part of the
action does not contain positive powers of the derivatives. We interpret this
as the fact that the two point Green functions vanish for nearby points, where
the proximity scale is given by the inverse of the cutoff
Classical and Quantum-like approaches to Charged-Particle Fluids in a Quadrupole
A classical description of the dynamics of a dissipative charged-particle
fluid in a quadrupole-like device is developed. It is shown that the set of the
classical fluid equations contains the same information as a complex function
satisfying a Schrodinger-like equation in which Planck's constant is replaced
by the time-varying emittance, which is related to the time-varying temperature
of the fluid. The squared modulus and the gradient of the phase of this complex
function are proportional to the fluid density and to the current velocity,
respectively. Within this framework, the dynamics of an electron bunch in a
storage ring in the presence of radiation damping and quantum-excitation is
recovered. Furthermore, both standard and generalized (including dissipation)
coherent states that may be associated with the classical particle fluids are
fully described in terms of the above formalism.Comment: LaTex, to appear in Physica Script
Spectral Action from Anomalies
Starting from a theory of fermions moving in a fixed gauge and gravitational
background we implement the scale invariance of the theory. Upon quantization
the theory is anomalous but the anomaly can be cancelled by the addition of
another term to the action. This term comes out to be basically the Chamseddine
Connes spectral action introduced in the context of noncommutative geometry. An
alternative realization of the dilaton may involve a collective scalar mode of
all fermions accumulated in a {scale-noninvariant} dilaton action. The entire
spectral action describes gauge and Higgs fields coupled with gravity. Here
this action is coupled with a dilaton and we discuss how it relates to the
transition from the radiation to the electroweak broken phase via condensation
of Higgs fields.Comment: Proceedings of the Corfu Summer Institute on Elementary Particles and
Physics - Workshop on Non Commutative Field Theory and Gravity, September
8-12, 2010 Corfu Greec
Optimal Investment and Financial Strategies under Tax Rate Uncertainty
In this paper we apply a real-option model to study the effects of tax rate uncertainty on a firm's decisions. In doing so, we depart from the relevant literature, which focuses on fully equity-financed investment projects. By letting a representative firm borrow optimally, we show that debt finance not only encourages investment activities but can also substantially mitigate the effect of tax rate uncertainty on investment timing.Capital Levy, Corporate Taxation, Default Risk, Real Options
Coherent States for Particle Beams in the Thermal Wave Model
In this paper, by using an analogy among {\it quantum mechanics}, {\it
electromagnetic beam optics in optical fibers}, and {\it charge particle beam
dynamics}, we introduce the concept of {\it coherent states} for charged
particle beams in the framework of the {\it Thermal Wave Model} (TWM). We give
a physical meaning of the Gaussian-like coherent structures of charged particle
distribution that are both naturally and artificially produced in an
accelerating machine in terms of the concept of coherent states widely used in
quantum mechanics and in quantum optics. According to TWM, this can be done by
using a Schr\"{o}dinger-like equation for a complex function, the so-called
{\it beam wave function} (BWF), whose squared modulus is proportional to the
transverse beam density profile, where Planck's constant and the time are
replaced by the transverse beam emittance and by the propagation coordinate,
respectively. The evolution of the particle beam, whose initial BWF is assumed
to be the simplest coherent state (ground-like state) associated with the beam,
in an infinite 1-D quadrupole-like device with small sextupole and octupole
aberrations, is analytically and numerically investigated.Comment: 21 pages, Late
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