2,480 research outputs found
The Weak Mixing Angle From TeV Scale Quark-Lepton Unification
Unified theories based on an extended left-right symmetric group, , are constructed in five dimensions. The compactification scale
is assumed to be only a loop factor above the weak scale, so that the weak
mixing angle is predicted to be close to its tree level value of 0.239.
Boundary conditions in the 5th dimension break , removing powerful constraints from while allowing
a reliable calculation of the leading logarithm corrections to .
The compactification scale is expected in the 1--5 TeV region, depending on how
is broken. Two illustrative models are presented, and the
experimental signal of the gauge boson is discussed.Comment: 15 page
First principles investigation of finite-temperature behavior in small sodium clusters
A systematic and detailed investigation of the finite-temperature behavior of
small sodium clusters, Na_n, in the size range of n= 8 to 50 are carried out.
The simulations are performed using density-functional molecular-dynamics with
ultrasoft pseudopotentials. A number of thermodynamic indicators such as
specific heat, caloric curve, root-mean-square bond length fluctuation,
deviation energy, etc. are calculated for each of the clusters. Size dependence
of these indicators reveals several interesting features. The smallest clusters
with n= 8 and 10, do not show any signature of melting transition. With the
increase in size, broad peak in the specific heat is developed, which
alternately for larger clusters evolves into a sharper one, indicating a
solidlike to liquidlike transition. The melting temperatures show irregular
pattern similar to experimentally observed one for larger clusters [ M. Schmidt
et al., Nature (London) 393, 238 (1998) ]. The present calculations also reveal
a remarkable size-sensitive effect in the size range of n= 40 to 55. While
Na_40 and Na_55 show well developed peaks in the specific heat curve, Na_50
cluster exhibits a rather broad peak, indicating a poorly-defined melting
transition. Such a feature has been experimentally observed for gallium and
aluminum clusters [ G. A. Breaux et al., J. Am. Chem. Soc. 126, 8628 (2004); G.
A.Breaux et al., Phys. Rev. Lett. 94, 173401 (2005) ].Comment: 8 pages, 11 figure
Meta-Stable Brane Configuration and Gauged Flavor Symmetry
Starting from an N=1 supersymmetric electric gauge theory with the gauge
group Sp(N_c) x SO(2N_c') with fundamentals for the first gauge group factor
and a bifundamental, we apply Seiberg dual to the symplectic gauge group only
and arrive at the N=1 supersymmetric dual magnetic gauge theory with dual
matters including the gauge singlets and superpotential. By analyzing the
F-term equations of the dual magnetic superpotential, we describe the
intersecting brane configuration of type IIA string theory corresponding to the
meta-stable nonsupersymmetric vacua of this gauge theory.Comment: 16 pp, 3 figures; stability analysis in page 7 and 8 added and the
presentation improved; reduced bytes of figures and to appear in MPL
The Twin Higgs: Natural Electroweak Breaking from Mirror Symmetry
We present `twin Higgs models', simple realizations of the Higgs as a
pseudo-Goldstone boson that protect the weak scale from radiative corrections
up to scales of order 5 - 10 TeV. In the ultra-violet these theories have a
discrete symmetry which interchanges each Standard Model particle with a
corresponding particle which transforms under a twin or mirror Standard Model
gauge group. In addition, the Higgs sector respects an approximate global SU(4)
symmetry. When this global symmetry is broken, the discrete symmetry tightly
constrains the form of corrections to the pseudo-Goldstone Higgs potential,
allowing natural electroweak symmetry breaking. Precision electroweak
constraints are satisfied by construction. These models demonstrate that,
contrary to the conventional wisdom, stabilizing the weak scale does not
require new light particles charged under the Standard Model gauge groups.Comment: 5 pages. Updated to the journal versio
A study of Angstrom's turbidity parameters from solar radiation measurements in India
Values of Angstrom's turbidity coefficient β and the wavelength exponent α have been computed for a number of stations in India from pyrheliometric measurements of direct solar radiation, for the whole spectrum and for specified spectral regions using filters OG1, RG2 and RG8. Large seasonal variations are noticed in β, with high values in summer and low values in winter at all stations. Rainout and washout are effective in the removal of aerosols from the atmosphere and a marked fall is noticed in β after thunderstorms and after the onset of the monsoon at all stations. Values of at stations in the southern half of the subcontinent remain more or less constant throughout the year with a mean value of about 1.0, indicating that smaller haze particles predominate and the size distribution remains the same despite the large increase of turbidity in summer. In the northern half of the sub-continent, α shows seasonal variations with low values, sometimes becoming zero or negative in summer and the normally accepted values in winter. Over north and central India therefore, while smaller particles are more numerous in winter, large particles predominate in summer
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