64,270 research outputs found

### 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

### Supersymmetric three family chiral SU(6) grand unification model from F-theory

We obtain a supersymmetric three family chiral SU(6) grand unification model
with the global family symmetry SU(3)[family] from F-theory. This model has
nice features such as all the fermion masses are reasonably generated and there
results only one pair of Higgs doublets, realizing the doublet-triplet
splitting from the family symmetry SU(3)[family]. The proton hexality is
realized toward the proton stability problem. There is a room to fit the three
gauge couplings using the F-theory flux idea and we obtain the proton lifetime
in the 10^{36-37} yr region.Comment: 5 pages, to be published in Phys. Rev.

### Cosmological constant is probably adjustable in brane worlds

In the brane world scenario, possessing the self-tuning property of the
cosmological constant, we study the probability amplitude for an initial state
of the Universe to transform to final states with some curvatures. In the Kim,
Kyae and Lee model, there exists a finite range of parameters such that the
transition amplitude to a near flat universe is exponentially dominated by the
smallness of curvature, > e^{positive number}/{Lambda-bar}^2}, i.e. is
dominated by an almost flat universe of |Lambda-bar|<epsilon.Comment: 6 pages with 2 figure

### Charmonium levels near threshold and the narrow state X(3872) \to \pi^{+}\pi^{-}\jpsi

We explore the influence of open-charm channels on charmonium properties, and
profile the 1:3D2, 1:3D3 and 2:1P1 charmonium candidates for X(3872). The
favored candidates, the 1:3D2 and 1:3D3 levels, both have prominent radiative
decays. The 1:3D2 might be visible in the $D^{0}\bar{D}^{*0}$ channel, while
the dominant decay of the 1:3D3 state should be into $D\bar{D}$. We propose
that additional discrete charmonium levels can be discovered as narrow
resonances of charmed and anticharmed mesons.Comment: 8 pages, 6 figures, uses RevTeX and boxedeps; few transcription
errors corrected in Tables IV and VI, three entries added in Table V, updated
references. Version to appear in Phys. Rev.

### Low-frequency method for magnetothermopower and Nernst effect measurements on single crystal samples at low temperatures and high magnetic fields

We describe an AC method for the measurement of the longitudinal (Sxx) and
transverse (Sxy, i.e. Nernst) thermopower of mm-size single crystal samples at
low temperatures (T30 T). A low-frequency (33
mHz) heating method is used to increase the resolution, and to determine the
temperature gradient reliably in high magnetic fields. Samples are mounted
between two thermal blocks which are heated by a sinusoidal frequency f0 with a
p/2 phase difference. The phase difference between two heater currents gives a
temperature gradient at 2f0. The corresponding thermopower and Nernst effect
signals are extracted by using a digital signal processing method due. An
important component of the method involves a superconducting link, YBa2Cu3O7+d
(YBCO), which is mounted in parallel with sample to remove the background
magnetothermopower of the lead wires. The method is demonstrated for the quasi
two-dimensional organic conductor a-(BEDT-TTF)2KHg(SCN)4, which exhibits a
complex, magnetic field dependent ground state above 22.5 T at low
temperatures.Comment: 11 pages, 6 figures, 15 reference

### Leptogenesis origin of Dirac gaugino dark matter

The Dirac nature of the gauginos (and also the Higgsinos) can be realized in
$R$-symmetric supersymmetry models. In this class of models, the Dirac bino (or
wino) with a small mixture of the Dirac Higgsinos is a good dark matter
candidate. When the seesaw mechanism with Higgs triplet superfields is
implemented to account for the neutrino masses and mixing, the leptogenesis
driven by the heavy triplet decay is shown to produce not only the
matter-antimatter asymmetry but also the asymmetric relic density of the Dirac
gaugino dark matter. The dark matter mass turns out to be controlled by the
Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the
weak scale for a mild hierarchy of the Yukawa couplings.Comment: 9 pages. Restructured for clear presentation, corrected some errors
and typos. No change in conclusio

### Putative spin liquid in the triangle-based iridate Ba$_3$IrTi$_2$O$_9$

We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte

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