1,163 research outputs found
What determines the distribution of shallow convective mass flux through cloud base?
The distribution of cloud-base mass flux is studied using large-eddy
simulations (LES) of two reference cases, one representing conditions over the
tropical ocean, and another one representing mid-latitude conditions over land.
To examine what sets the difference between the two distributions, nine
additional LES cases are set up as variations of the two reference cases. We
find that the total surface heat flux and its changes over the diurnal cycle do
not influence the distribution shape. The latter is also not determined by the
level of organization in the cloud field. It is instead determined by the ratio
of the surface sensible heat flux to the latent heat flux, the Bowen ratio .
sets the thermodynamic efficiency of the moist convective heat cycle, which
determines the portion of the total surface heat flux that can be transformed
into mechanical work of convection against mechanical dissipation. The
thermodynamic moist heat cycle sets the average mass flux per cloud , and through it also controls the shape of the
distribution. An expression for is derived based on the
moist convective heat cycle and is evaluated against LES. This expression can
be used in shallow cumulus parameterizations as a physical constraint on the
mass flux distribution. The similarity between the mass flux and the cloud area
distributions indicate that also has a role in shaping the cloud area
distribution, which could explain its different shapes and slopes observed in
previous studies.Comment: submitted to J. Atmos. Sci., revise
Basis invariant measure of CP-violation and renormalization
We analyze, in the context of a simple toy model, for which renormalization
schemes the CP-properties of bare Lagrangian and its finite part coincide. We
show that this is the case for the minimal subtraction and on-shell schemes.
The CP-properties of the theory can then be characterized by CP-odd basis
invariants expressed in terms of renormalized masses and couplings. For the
minimal subtraction scheme we furthermore show that in CP-conserving theories
the CP-odd basis invariants are zero at any scale but are not renormalization
group invariant in CP-violating ones.Comment: 5 page
N=4 Topological Amplitudes and Black Hole Entropy
We study the effects of N=4 topological string amplitudes on the entropy of
black holes. We analyse the leading contribution associated to six-derivative
terms and find one particular operator which can correct the entropy of N=4
black holes. This operator is BPS-like and appears in the effective action of
type II string theory on K3 x T^2 or equivalently its heterotic dual on T^6. In
both descriptions the leading contribution arises at one-loop, which we
calculate explicitly on the heterotic side. We then consider whether this term
has any consequences for the entropy of (large) N=4 black holes and find that
it makes indeed a contribution at subleading order. Repeating the computation
for small black holes with vanishing horizon area at the classical level, we
prove that this coupling lifts certain flat directions in the entropy function
thereby being responsible for the attractor equations of some moduli fields.Comment: 33 pages, references added, section 3.3 adde
Leptogenesis in crossing and runaway regimes
We study the impact of effective thermal masses and widths on resonant
leptogenesis. We identify two distinct possibilities which we refer to as
crossing and runaway regimes. In the runaway regime the mass difference grows
monotonously with temperature, whereas it initially decreases in the crossing
regime, such that the effective masses become equal at some temperature.
Following the conventional logic the source of the asymmetry would vanish in
the latter case. Using non-equilibrium quantum field theory, we analytically
demonstrate that the vanishing of the difference of the effective masses does
however neither imply a suppression nor a strong enhancement of the source for
the lepton asymmetry. In the vicinity of the crossing point the asymmetry
calculated in an (improved) Boltzmann limit develops a spurious peak, which
signals the breakdown of the quasiparticle approximation. In the exact result
this spurious enhancement is compensated by coherent transitions between the
two mass shells. Despite the breakdown of the quasiparticle approximation
off-shell contributions remain negligibly small even at the crossing point.Comment: 41 pages, 9 figures, figures 3 and 6 are animation
A Generalisation For The Infinite Integral Over Three Spherical Bessel Functions
A new formula is derived that generalises an earlier result for the infinite
integral over three spherical Bessel functions. The analytical result involves
a finite sum over associated Legendre functions, , of degree and
order . The sum allows for values of that are greater than . A
generalisation for the associated Legendre functions to allow for any rational
for a specific is also shownComment: Published in J. Phys. A: Math. Theor. 43 (2010) 45520
Medium corrections to the CP-violating parameter in leptogenesis
In two recent papers, arXiv:0909.1559 and arXiv:0911.4122, it has been
demonstrated that one can obtain quantum corrected Boltzmann kinetic equations
for leptogenesis using a top-down approach based on the
Schwinger-Keldysh/Kadanoff-Baym formalism. These "Boltzmann-like" equations are
similar to the ones obtained in the conventional bottom-up approach but differ
in important details. In particular there is a discrepancy between the
CP-violating parameter obtained in the first-principle derivation and in the
framework of thermal field theory. Here we demonstrate that the two approaches
can be reconciled if causal n-point functions are used in the thermal field
theory approach. The new result for the medium correction to the CP-violating
parameter is qualitatively different from the conventional one. The analogy to
a toy model considered earlier enables us to write down consistent quantum
corrected Boltzmann equations for thermal leptogenesis in the Standard Model
(supplemented by three right-handed neutrinos) which include quantum
statistical terms and medium corrected expressions for the CP-violating
parameter.Comment: 13 pages, 9 figure
M String, Monopole String and Modular Forms
We study relations between M-strings (one-dimensional intersections of
M2-branes and M5-branes) in six dimensions and m-strings (magnetically charged
monopole strings) in five dimensions. For specific configurations, we propose
that the counting functions of BPS bound-states of M-strings capture the
elliptic genus of the moduli space of m-strings. We check this proposal for the
known cases, the Taub-NUT and Atiyah-Hitchin spaces for which we find complete
agreement. Furthermore, we analyze the modular properties of the M-string free
energies, which do not transform covariantly under SL(2,Z). However, for a
given number of M-strings, we find that there exists a unique combination of
unrefined genus-zero free energies that transforms as a Jacobi form under a
congruence subgroup of SL(2,Z). These combinations correspond to summing over
different numbers of M5-branes and make sense only if the distances between
them are all equal. We explain that this is a necessary condition for the
m-string moduli space to be factorizable into relative and center-of-mass
parts.Comment: 80 pages, 4 embedded figures, 5 long tables; v2. typos fixed; v3.
published version with title chang
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