220,758 research outputs found

### Self-tuning of cosmological constant and exit from inflation

I review the recent 5D self-tuning solutions of the cosmological constant
problem, and try to unify two cosmological constant problems within the
framework of the self-tuning solutions. One problem, the large cosmological
constant needed for inflation, is interpreted by starting with the parameters
allowing only the dS vacuum, and the vanishing cosmological constant at a true
vacuum is realized by changing parameters by exit from inflation at the brane
such that the self-tuning solution is allowed.Comment: Latex file of 8 pages, including 2 figures. Talk presented at
COSPA-03, Taipei, Taiwan, Nov. 13-15, 200

### Brane gravity, massless bulk scalar and self-tuning of the cosmological constant

We show that a self-tuning mechanism of the cosmological constant could work
in 5D non-compact space-time with a $Z_2$ symmetry in the presence of a
massless scalar field. The standard model matter fields live only on the 4D
brane. The change of vacuum energy on the brane (brane cosmological constant)
by, for instance, electroweak and QCD phase transitions, just gives rise to
dynamical shifts of the profiles of the background metric and the scalar field
in the extra dimension, keeping 4D space-time flat without any fine-tuning. To
avoid naked singularities in the bulk, the brane cosmological constant should
be negative. We introduce an additional brane-localized 4D Einstein-Hilbert
term so as to provide the observed 4D gravity with the non-compact extra
dimension. With a general form of brane-localized gravity term allowed by the
symmetries, the low energy Einstein gravity is successfully reproduced on the
brane at long distances. We show this phenomenon explicitly for the case of
vanishing bulk cosmological constant.Comment: 1+15 pages, no figure, Version to appear in PR

### Statistical theory of plasma turbulence

We present a statistical theory of intermittency in plasma turbulence based on short-lived coherent structures (instantons). In general, the probability density functions (PDFs) of the flux R are shown to have an exponential scaling P(R) ∝ exp (-cRs ) in the tails. In ion-temperature-gradient turbulence, the exponent takes the value s = 3/2 for momentum flux and s = 3 for zonal flow formation. The value of s follows from the order of the highest nonlinear interaction term and the moments for which the PDFs are computed. The constant c depends on the spatial profile of the coherent structure and other physical parameters in the model. Our theory provides a powerful mechanism for ubiquitous exponential scalings of PDFs, often observed in various tokamaks. Implications of the results, in particular, on structure formation are further discussed

Recommended from our members

### Introduction: Reflections on nancy abelmann's legacy

Nancy Abelmann passed away on January 6, 2016, at the age of fifty-six. She received her PhD from the University of California, Berkeley in 1990, after completing her dissertation under Nelson Graburn. That same year, she was hired by the University of Illinois, Urbana-Champaign, where she worked for two and a half decades. She was a beloved teacher, mentor, and colleague to many, and she was a key figure in multiple departments and centers. At the time of her death, she held the Harold E. Preble Professorship in Anthropology, Asian American Studies, East Asian Languages and Cultures, and Women and Gender Studies and was also Associate Vice Chancellor for Research

### An ultralight pseudoscalar boson

Using a fundamental discrete symmetry, $\mathbb{Z}_N$, we construct a
two-axion model with the QCD axion solving the strong-$CP$ problem, and an
ultralight axion (ULA) with $m_{\rm ULA}\approx 10^{-22}\text{ eV}$ providing
the dominant form of dark matter (DM). The ULA is light enough to be detectable
in cosmology from its imprints on structure formation, and may resolve the
small-scale problems of cold DM. The necessary relative DM abundances occur
without fine tuning in constructions with decay constants $f_{\rm ULA}\sim
10^{17}\text{ GeV}$, and $f_{\rm QCD}\sim 10^{11}\text{ GeV}$. An example model
achieving this has $N=24$, and we construct a range of other possibilities. We
compute the ULA couplings to the Standard Model, and discuss prospects for
direct detection. The QCD axion may be detectable in standard experiments
through the $\vec{E}\cdot\vec{B}$ and $G\tilde{G}$ couplings. In the simplest
models, however, the ULA has identically zero coupling to both $G\tilde{G}$ of
QCD and $\vec{E}\cdot\vec{B}$ of electromagnetism due to vanishing
electromagnetic and color anomalies. The ULA couples to fermions with strength
$g\propto 1/f_{\rm ULA}$. This coupling causes spin precession of nucleons and
electrons with respect to the DM wind with period $t\sim$months. Current limits
do not exclude the predicted coupling strength, and our model is within reach
of the CASPEr-Wind experiment, using nuclear magnetic resonance.Comment: 14 pages, 3 figures. v2 numerical error on N corrected, conclusions
unchanged. Typos and notation corrected. Matches version published in PR

### Z_{12-I} Orbifold Compactification toward SUSY Standard Model

We explain the orbifold compactification in string models and present a
Z_{12-I} orbifold compactification toward supersymmetric standard models. We
also point out an effective R-parity from this string construction. The VEVs of
gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at
LHC", Cairo, 11-14 March 200

### Counting minimal generator matrices

Given a particular convolutional code C, we wish to find all minimal generator matrices G(D) which represent that code. A standard form S(D) for a minimal matrix is defined, and then all standard forms for the code C are counted (this is equivalent to counting special pre-multiplication matrices P(D)). It is shown that all the minimal generator matrices G(D) are contained within the 'ordered row permutations' of these standard forms, and that all these permutations are distinct. Finally, the result is used to place a simple upper bound on the possible number of convolutional codes

### $Z_N$ orbifold compactifications in $AdS_6$ with Gauss-Bonnet term

We present a general setup for junctions of semi-infinite 4-branes in $AdS_6$
with the Gauss-Bonnet term. The 3-brane tension at the junction of 4-branes can
be nonzero. Using the brane junctions as the origin of the $Z_N$ discrete
rotation symmetry, we identify 3-brane tensions at three fixed points of the
orbifold $T^2/Z_3$ in terms of the 4-brane tensions. As a result, the three
3-brane tensions can be simultaneously positive, which enables us to explain
the mass hierarchy by taking one of two branes apart from the hidden brane as
the visible brane, and hence does not introduce a severe cosmological problem.Comment: Latex file of 20 pages including 2 figure

### Self-tuning of the cosmological constant

Here, I discuss the cosmological constant (CC) problems, in particular paying
attention to the vanishing cosmological constant. There are three cosmological
constant problems in particle physics. Hawking's idea of calculating the
probability amplitude for our Universe is peaked at CC = 0 which I try to
obtain after the initial inflationary period using a self-tuning model. I
review what has been discussed on the Hawking type calculation, and present a
(probably) correct way to calculate the amplitude, and show that the
Kim-Kyae-Lee self-tuning model allows a finite range of parameters for the CC =
0 to have a singularly large probability, approached from the AdS side.Comment: 12 pages with 8 figure

- …