The Weak Mixing Angle From TeV Scale Quark-Lepton Unification

Unified theories based on an extended left-right symmetric group, $SU(4) \times SU(2)^4$, 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 $SU(4) \to SU(3) \times U(1)_{B-L}$, removing powerful constraints from $K_L \to \mu e$ while allowing a reliable calculation of the leading logarithm corrections to $\sin^2 \theta$. The compactification scale is expected in the 1--5 TeV region, depending on how $SU(2)^4$ is broken. Two illustrative models are presented, and the experimental signal of the $Z'$ 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