220,758 research outputs found

    Self-tuning of cosmological constant and exit from inflation

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    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

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    We show that a self-tuning mechanism of the cosmological constant could work in 5D non-compact space-time with a Z2Z_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

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    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

    An ultralight pseudoscalar boson

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    Using a fundamental discrete symmetry, ZN\mathbb{Z}_N, we construct a two-axion model with the QCD axion solving the strong-CPCP problem, and an ultralight axion (ULA) with mULA1022 eVm_{\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 fULA1017 GeVf_{\rm ULA}\sim 10^{17}\text{ GeV}, and fQCD1011 GeVf_{\rm QCD}\sim 10^{11}\text{ GeV}. An example model achieving this has N=24N=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 EB\vec{E}\cdot\vec{B} and GG~G\tilde{G} couplings. In the simplest models, however, the ULA has identically zero coupling to both GG~G\tilde{G} of QCD and EB\vec{E}\cdot\vec{B} of electromagnetism due to vanishing electromagnetic and color anomalies. The ULA couples to fermions with strength g1/fULAg\propto 1/f_{\rm ULA}. This coupling causes spin precession of nucleons and electrons with respect to the DM wind with period tt\simmonths. 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

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    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

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    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

    ZNZ_N orbifold compactifications in AdS6AdS_6 with Gauss-Bonnet term

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    We present a general setup for junctions of semi-infinite 4-branes in AdS6AdS_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 ZNZ_N discrete rotation symmetry, we identify 3-brane tensions at three fixed points of the orbifold T2/Z3T^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

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    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
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