7,709 research outputs found
The Rise in Firm-Level Volatility: Causes and Consequences
We document that the recent decline in aggregate volatility has been accompanied by a large increase in firm level risk. The negative relationship between firm and aggregate risk seems to be present across industries in the US, and across OECD countries. Firm volatility increases after deregulation. Firm volatility is linked to research and development spending as well as access to external financing. Further, R&D intensity is also associated with lower correlation of sectoral growth with the rest of the economy.
Cosmological perturbation theory at three-loop order
We analyze the dark matter power spectrum at three-loop order in standard
perturbation theory of large scale structure. We observe that at late times the
loop expansion does not converge even for large scales (small momenta) well
within the linear regime, but exhibits properties compatible with an asymptotic
series. We propose a technique to restore the convergence in the limit of small
momentum, and use it to obtain a perturbative expansion with improved
convergence for momenta in the range where baryonic acoustic oscillations are
present. Our results are compared with data from N-body simulations at
different redshifts, and we find good agreement within this range.Comment: 29 pages, 8 figures, 1 table; v2 Typos corrected, references added.
Matches published versio
Periodic Mean-Field Solutions and the Spectra of Discrete Bosonic Fields: Trace Formula for Bose-Hubbard Models
We consider the many-body spectra of interacting bosonic quantum fields on a
lattice in the semiclassical limit of large particle number . We show that
the many-body density of states can be expressed as a coherent sum over
oscillating long-wavelength contributions given by periodic, non-perturbative
solutions of the, typically non-linear, wave equation of the classical
(mean-field) limit. To this end we construct the semiclassical approximation
for both the smooth and oscillatory part of the many-body density of states in
terms of a trace formula starting from the exact path integral form of the
propagator between many-body quadrature states. We therefore avoid the use of a
complexified classical limit characteristic of the coherent state
representation. While quantum effects like vacuum fluctuations and gauge
invariance are exactly accounted for, our semiclassical approach captures
quantum interference and therefore is valid well beyond the Ehrenfest time
where naive quantum-classical correspondence breaks down. Remarkably, due to a
special feature of harmonic systems with incommesurable frequencies, our
formulas are generically valid also in the free-field case of non-interacting
bosons.Comment: submitted to Phys. Rev.
Chiral anomalies on a circle and their cancellation in F-theory
We study in detail how four-dimensional local anomalies manifest themselves
when the theory is compactified on a circle. By integrating out the
Kaluza-Klein modes in a way that preserves the four-dimensional symmetries in
the UV, we show that the three-dimensional theory contains field-dependent
Chern-Simons terms that appear at one-loop. These vanish if and only if the
four-dimensional anomaly is canceled, so the anomaly is not lost upon
compactification. We extend this analysis to situations where anomalies are
canceled through a Green-Schwarz mechanism. We then use these results to show
automatic cancellation of local anomalies in F-theory compactifications that
can be obtained as a limit of M-theory on a smooth Calabi-Yau fourfold with
background flux.Comment: 39 pages, 3 figures. v2: references added and typos correcte
The semiclassical propagator in fermionic Fock space
We present a rigorous derivation of a semiclassical propagator for
anticommuting (fermionic) degrees of freedom, starting from an exact
representation in terms of Grassmann variables. As a key feature of our
approach the anticommuting variables are integrated out exactly, and an exact
path integral representation of the fermionic propagator in terms of commuting
variables is constructed. Since our approach is not based on auxiliary
(Hubbard-Stratonovich) fields, it surpasses the calculation of fermionic
determinants yielding a standard form with real actions for the propagator. These two features
allow us to provide a rigorous definition of the classical limit of interacting
fermionic fields and therefore to achieve the long-standing goal of a
theoretically sound construction of a semiclassical van Vleck-Gutzwiller
propagator in fermionic Fock space. As an application, we use our propagator to
investigate how the different universality classes (orthogonal, unitary and
symplectic) affect generic many-body interference effects in the transition
probabilities between Fock states of interacting fermionic systems.Comment: 20 pages, 1 figur
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