13,333 research outputs found

### A note on dark energy induced by D-brane motion

In this note we study the possibility of obtaining dark energy solution in a
D-brane scenario in a warped background that includes brane-position dependent
corrections for the non-perturbative superpotential. The volume modulus is
stabilized at instantaneous minima of the potential. Though the model can
account for the existence of dark energy within present observational bound -
fine-tuning of the model parameters becomes unavoidable. Moreover, the model
does not posses a tracker solution.Comment: 5 pages, 4 figure

### Power conditioning techniques

The technological developments required to reduce the electrical power system component weights from the state-of-the-art 2.0 kg/kW to the range of 0.1 to 0.2 kg/kW are discussed. Power level requirements and their trends in aerospace applications are identified and presented. The projected weight and launch costs for a 1MW power converter built using state-of-the-art technology are established to illustrate the need for reliable, ultralightweight advanced power components. The key factors affecting converter weight are given and some of the tradeoffs between component ratings and circuit topology are identified. The weight and launch costs for a 1MW converter using 0.1 kg/kW technology are presented. Finally, the objectives and goals of the Multi-Megawatt Program at the NASA Lewis Research Center, which is funded by the SDIO through the Air Force, are given

### Desensitizing Inflation from the Planck Scale

A new mechanism to control Planck-scale corrections to the inflationary eta
parameter is proposed. A common approach to the eta problem is to impose a
shift symmetry on the inflaton field. However, this symmetry has to remain
unbroken by Planck-scale effects, which is a rather strong requirement on
possible ultraviolet completions of the theory. In this paper, we show that the
breaking of the shift symmetry by Planck-scale corrections can be
systematically suppressed if the inflaton field interacts with a conformal
sector. The inflaton then receives an anomalous dimension in the conformal
field theory, which leads to sequestering of all dangerous high-energy
corrections. We analyze a number of models where the mechanism can be seen in
action. In our most detailed example we compute the exact anomalous dimensions
via a-maximization and show that the eta problem can be solved using only
weakly-coupled physics.Comment: 34 pages, 3 figures

### A necessary extension of the surface flux transport model

Customary two-dimensional flux transport models for the evolution of the
magnetic field at the solar surface do not account for the radial structure and
the volume diffusion of the magnetic field. When considering the long-term
evolution of magnetic flux, this omission can lead to an unrealistic long-term
memory of the system and to the suppression of polar field reversals. In order
to avoid such effects, we propose an extension of the flux transport model by a
linear decay term derived consistently on the basis of the eigenmodes of the
diffusion operator in a spherical shell. A decay rate for each eigenmode of the
system is determined and applied to the corresponding surface part of the mode
evolved in the flux transport model. The value of the volume diffusivity
associated with this decay term can be estimated to be in the range 50--100
km^2/s by considering the reversals of the polar fields in comparison of flux
transport simulations with observations. We show that the decay term prohibits
a secular drift of the polar field in the case of cycles of varying strength,
like those exhibited by the historical sunspot record.Comment: for further information visit: http://solweb.oma.be/users/baumann

### Above the Law: The Prosecutor\u27s Duty to Seek Justice and the Performance of Substantial Assistance Agreements

We study the gravitational-wave (GW) signatures of clouds of ultralight bosons around black holes (BHs) in binary inspirals. These clouds, which are formed via superradiance instabilities for rapidly rotating BHs, produce distinct effects in the population of BH masses and spins, and, for real fields, a continuous monochromatic GW signal. We show that the presence of a binary companion greatly enriches the dynamical evolution of the system, most remarkably through the existence of resonant transitions between the growing and decaying modes of the cloud (analogous to Rabi oscillations in atomic physics). These resonances have rich phenomenological implications for current and future GW detectors. Notably, the amplitude of the GW signal from the clouds may be reduced, and in many cases terminated, much before the binary merger. The presence of a boson cloud can also be revealed in the GW signal from the binary through the imprint of finite-size effects, such as spin-induced multipole moments and tidal Love numbers. The time dependence of the cloud's energy density during the resonance leads to a sharp feature, or at least attenuation, in the contribution from the finite-size terms to the waveforms. The observation of these effects would constrain the properties of putative ultralight bosons through precision GW data, offering new probes of physics beyond the Standard Model

### HOG PRICES RECEIVED AND THE VALUE OF INFORMATION: A LOGIT ANALYSIS

The study discussed in this paper integrates the economics of information, production theory, and the theory of human capital to determine the optimum amount of price information collected by profit maximizing hog producers.Livestock Production/Industries,

### A Field Range Bound for General Single-Field Inflation

We explore the consequences of a detection of primordial tensor fluctuations
for general single-field models of inflation. Using the effective theory of
inflation, we propose a generalization of the Lyth bound. Our bound applies to
all single-field models with two-derivative kinetic terms for the scalar
fluctuations and is always stronger than the corresponding bound for slow-roll
models. This shows that non-trivial dynamics can't evade the Lyth bound. We
also present a weaker, but completely universal bound that holds whenever the
Null Energy Condition (NEC) is satisfied at horizon crossing.Comment: 16 page

### New features in curvaton model

We demonstrate novel features in the behavior of the second and third order
non-linearity parameters of the curvature perturbation, namely, $f_{NL}$ and
$g_{NL}$, arising from non-linear motion of curvaton field. We investigate two
classes of potentials for the curvaton - the first has tiny oscillations
super-imposed upon the quadratic potential. The second is characterized by a
single 'feature' separating two quadratic regimes with different mass scales.
The feature may either be a bump or a flattening of the potential. In the case
of the oscillatory potential we find that as the width and height of
superimposed oscillations increase, both $f_{NL}$ and $g_{NL}$ deviate strongly
from their expected values from a quadratic potential. $f_{NL}$ changes sign
from positive to negative as the oscillations in the potential become more
prominent. Hence, this model can be severely constrained by convincing evidence
from observations that $f_{NL}$ is positive. $g_{NL}$, on the other hand,
acquires very large negative values. For the the single feature potential, we
find that $f_{NL}$ and $g_{NL}$ exhibit oscillatory behavior as a function of
the parameter that controls the feature.Comment: 1+14 pages, 5 figure

### Nonsupersymmetric brane vacua in stabilized compactifications

We derive the equations for the nonsupersymmetric vacua of D3-branes in the
presence of nonperturbative moduli stabilization in type IIB flux
compactifications, and solve and analyze them in the case of two particular
7-brane embeddings at the bottom of the warped deformed conifold. In the limit
of large volume and long throat, we obtain vacua by imposing a constraint on
the 7-brane embedding. These vacua fill out continuous spaces of higher
dimension than the corresponding supersymmetric vacua, and have negative
effective cosmological constant. Perturbative stability of these vacua is
possible but not generic. Finally, we argue that anti-D3-branes at the tip of
the conifold share the same vacua as D3-branes.Comment: 17 pages, 1 figure, LaTeX. v2: references added, typo fixed. v3:
version appearing in JHE

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