14,188 research outputs found
In Praise of Tax Havens: International Tax Planning and Foreign Direct Investment
The multinationalization of corporate investment in recent years has given rise to a number of international tax avoidance schemes that may be eroding tax revenues in industrialized countries, but which may also reduce tax burdens on mobile capital and so facilitate investment. Both the welfare effects of and the optimal response to international tax planning are therefore ambiguous. Evaluating these factors in a simple general equilibrium model, we find that citizens of high-tax countries benefit from (some) tax planning. Paradoxically, if tax rates are not too high, an increase in tax planning activity causes a rise in optimal corporate tax rates, and a decline in multinational investment. Thus fears of a “race to the bottom” in corporate tax rates may be misplaced.income shifting, tax planning, foreign direct investment, tax competition, thin capitalization
Off-shell hydrodynamics from holography
We outline a program for obtaining an action principle for dissipative fluid
dynamics by considering the holographic Wilsonian renormalization group applied
to systems with a gravity dual. As a first step, in this paper we restrict to
systems with a non-dissipative horizon. By integrating out gapped degrees of
freedom in the bulk gravitational system between an asymptotic boundary and a
horizon, we are led to a formulation of hydrodynamics where the dynamical
variables are not standard velocity and temperature fields, but the relative
embedding of the boundary and horizon hypersurfaces. At zeroth order, this
action reduces to that proposed by Dubovsky et al. as an off-shell formulation
of ideal fluid dynamics.Comment: 34 pages, 2 figures; v2: references added, clarifications added in
Sec. I
Does electronic coherence enhance anticorrelated pigment vibrations under realistic conditions?
The light-harvesting efficiency of a photoactive molecular complex is largely
determined by the properties of its electronic quantum states. Those, in turn,
are influenced by molecular vibrational states of the nuclear degrees of
freedom. Here, we reexamine two recently formulated concepts that a coherent
vibronic coupling between molecular states would either extend the electronic
coherence lifetime or enhance the amplitude of the anticorrelated vibrational
mode at longer times. For this, we study a vibronically coupled dimer and
calculate the nonlinear two-dimensional (2D) electronic spectra which directly
reveal electronic coherence. The timescale of electronic coherence is initially
extracted by measuring the anti-diagonal bandwidth of the central peak in the
2D spectrum at zero waiting time. Based on the residual analysis, we identify
small-amplitude long-lived oscillations in the cross-peaks, which, however, are
solely due to groundstate vibrational coherence, regardless of having resonant
or off-resonant conditions. Our studies neither show an enhancement of the
electronic quantum coherence nor an enhancement of the anticorrelated
vibrational mode by the vibronic coupling under ambient conditions
A note on color neutrality in NJL-type models
By referring to the underlying physics behind the color charge neutrality
condition in quark matter, we discuss how this condition should be properly
imposed in NJL-type models in a phenomenologically meaningful way. In
particular, we show that the standard assumption regarding the use of two color
chemical potentials, chosen in a very special way, is not justified in general.
When used uncritically, such an approach leads to wrong or unphysical
conclusions.Comment: 4 pages, no figure; v2: minor clarifications, references adde
An efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes
We combine the coherent modified Redfield theory (CMRT) with the equation of
motion-phase matching approach (PMA) to calculate two-dimensional photon echo
spectra for photoactive molecular complexes with an intermediate strength of
the coupling to their environment. Both techniques are highly efficient, yet
they involve approximations at different levels. By explicitly comparing with
the numerically exact quasi-adiabatic path integral approach, we show for the
Fenna-Matthews-Olson complex that the CMRT describes the decay rates in the
population dynamics well, but final stationary populations and the oscillation
frequencies differ slightly. In addition, we use the combined CMRT+PMA to
calculate two-dimensional photon-echo spectra for a simple dimer model. We find
excellent agreement with the exact path integral calculations at short waiting
times where the dynamics is still coherent. For long waiting times, differences
occur due to different final stationary states, specifically for strong
system-bath coupling. For weak to intermediate system-bath couplings, which is
most important for natural photosynthetic complexes, the combined CMRT+PMA
gives reasonable results with acceptable computational efforts
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