21,033 research outputs found
Eternal Inflation with alpha'-Corrections
Higher-order alpha'-corrections are a generic feature of type IIB string
compactifications. In KKLT-like models of moduli stabilization they provide a
mechanism of breaking the no-scale structure of the volume modulus. We present
a model of inflation driven by the volume modulus of flux compactifications of
the type IIB superstring. Using the effects of gaugino condensation on
D7-branes and perturbative alpha'-corrections the volume modulus can be
stabilized in a scalar potential which simultaneously contains saddle points
providing slow-roll inflation with about 130 e-foldings. We can accommodate the
3-year WMAP data with a spectral index of density fluctuations n_s=0.93. Our
model allows for eternal inflation providing the initial conditions of
slow-roll inflation.Comment: 24 pages, 5 figures, LaTeX, v4: includes comparison with 3-year WMAP
data and values for the tensor ratio r and the running of n_
A Stable Fountain Code Mechanism for Peer-to-Peer Content Distribution
Most peer-to-peer content distribution systems require the peers to privilege
the welfare of the overall system over greedily maximizing their own utility.
When downloading a file broken up into multiple pieces, peers are often asked
to pass on some possible download opportunities of common pieces in order to
favor rare pieces. This is to avoid the missing piece syndrome, which throttles
the download rate of the peer-to-peer system to that of downloading the file
straight from the server. In other situations, peers are asked to stay in the
system even though they have collected all the file's pieces and have an
incentive to leave right away.
We propose a mechanism which allows peers to act greedily and yet stabilizes
the peer-to-peer content sharing system. Our mechanism combines a fountain code
at the server to generate innovative new pieces, and a prioritization for the
server to deliver pieces only to new peers. While by itself, neither the
fountain code nor the prioritization of new peers alone stabilizes the system,
we demonstrate that their combination does, through both analytical and
numerical evaluation.Comment: accepted to IEEE INFOCOM 2014, 9 page
String Cosmology - Large-Field Inflation in String Theory
This is a short review of string cosmology. We wish to connect string-scale
physics as closely as possible to observables accessible to current or
near-future experiments. Our possible best hope to do so is a description of
inflation in string theory. The energy scale of inflation can be as high as
that of Grand Unification (GUT). If this is the case, this is the closest we
can possibly get in energy scales to string-scale physics. Hence, GUT-scale
inflation may be our best candidate phenomenon to preserve traces of
string-scale dynamics. Our chance to look for such traces is the primordial
gravitational wave, or tensor mode signal produced during inflation. For
GUT-scale inflation this is strong enough to be potentially visible as a B-mode
polarization of the cosmic microwave background (CMB). Moreover, a GUT-scale
inflation model has a trans-Planckian excursion of the inflaton scalar field
during the observable amount of inflation. Such large-field models of inflation
have a clear need for symmetry protection against quantum corrections. This
makes them ideal candidates for a description in a candidate fundamental theory
like string theory. At the same time the need of large-field inflation models
for UV completion makes them particularly susceptible to preserve imprints of
their string-scale dynamics in the inflationary observables, the spectral index
and the fractional tensor mode power . Hence, we will focus this
review on axion monodromy inflation as a mechanism of large-field inflation in
string theory.Comment: 34 pages, 1 figure, LaTeX, v2: typos fixed, 3 references added,
agrees with published version in "Perspectives in String Phenomenology" and
"International Journal of Modern Physics A
Philanthropic Foundations: Growing Funders of the News
Updates April 2008 discussions on the role of foundations in supporting journalism, including creating journalism units within NGOs, collaborations with for-profit news organizations, and investment in local news sites and news and information nonprofits
On the Benefit of Information Centric Networks for Traffic Engineering
Current Internet performs traffic engineering (TE) by estimating traffic
matrices on a regular schedule, and allocating flows based upon weights
computed from these matrices. This means the allocation is based upon a guess
of the traffic in the network based on its history. Information-Centric
Networks on the other hand provide a finer-grained description of the traffic:
a content between a client and a server is uniquely identified by its name, and
the network can therefore learn the size of different content items, and
perform traffic engineering and resource allocation accordingly. We claim that
Information-Centric Networks can therefore provide a better handle to perform
traffic engineering, resulting in significant performance gain.
We present a mechanism to perform such resource allocation. We see that our
traffic engineering method only requires knowledge of the flow size (which, in
ICN, can be learned from previous data transfers) and outperforms a min-MLU
allocation in terms of response time. We also see that our method identifies
the traffic allocation patterns similar to that of min-MLU without having
access to the traffic matrix ahead of time. We show a very significant gain in
response time where min MLU is almost 50% slower than our ICN-based TE method
Moduli Stabilization in Meta-Stable Heterotic Supergravity Vacua
We revisit the issue of moduli stabilization in a class of N=1 four
dimensional supergravity theories which are low energy descriptions of standard
perturbative heterotic string vacua compactified on Calabi-Yau spaces. In
particular, we show how it is possible to stabilize the universal dilaton and
Kahler moduli in a de Sitter/Minkowski vacuum with low energy supersymmetry
breaking by means of non-perturbative gauge dynamics, including recent results
by Intriligator, Seiberg and Shih. The non-SUSY vacua are meta-stable but
sufficiently long-lived.Comment: 1+31 pages, LaTeX, uses JHEP3 class, v2: references corrected and
added, version published in JHE
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