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    Branes in the M_D x M_d+ x M_d- Compactification of Type II String on S^1/Z_2 and Their Cosmologicval Applications
    (2010-07-09T15:21:00Z) Devin, Michael J.; Ali, Tibra; Cleaver, Gerald B.; Wang, Anzhong.; Wu, Qiang, 1977-
    In this paper, we study the implementation of brane worlds in type II string theory. Starting with the NS/NS sector of type II string, we first compactify the (D + d+ + d−)-dimensional spacetime, and reduce the corresponding action to a D-dimensional effective action, where the topologies of Md+ and Md− are arbitrary. We further compactify one of the (D − 1) spatial dimensions on an S1/Z2 orbifold, and derive the gravitational and matter field equations both in the bulk and on the branes. Then, we investigate two key issues in such a setup: (i) the radion stability and radion mass; and (ii) the localization of gravity, and the corresponding Kaluza-Klein (KK) modes. We show explicitly that the radion is stable and its mass can be in the order of GeV . In addition, the gravity is localized on the visible brane, and its spectrum of the gravitational KK towers is discrete and can have a mass gap of T eV , too. The high order Yukawa corrections to the 4-dimensional Newtonian potential is exponentially suppressed, and can be negligible. Applying such a setup to cosmology, we obtain explicitly the field equations in the bulk and the generalized Friedmann equations on the branes.
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    A Simple Introduction to Particle Physics: Part II Geometric Foundations and Relativity
    (2010-07-09T15:12:17Z) Robinson, Matthew Brandon, 1981-; Ali, Tibra; Cleaver, Gerald B.
    This is the second in a series of papers intended to provide a basic overview of some of the major ideas in particle physics. Part I [40] was primarily an algebraic exposition of gauge theories. We developed the group theoretic tools needed to understand the basic construction of gauge theory, as well as the physical concepts and tools to understand the structure of the Standard Model of Particle Physics as a gauge theory. In this paper (and the paper to follow), we continue our emphasis on gauge theories, but we do so with a more geometrical approach. We will conclude this paper with a brief discussion of general relativity, and save more advanced topics (including fibre bundles, characteristic classes, etc.) for the next paper in the series. We wish to reiterate that these notes are not intended to be a comprehensive introduc- tion to any of the ideas contained in them. Their purpose is to introduce the “forest" rather than the “trees". The primary emphasis is on the algebraic/geometric/mathematical un- derpinnings rather than the calculational/phenomenological details. The topics were chosen according to the authors’ preferences and agenda. These notes are intended for a student who has completed the standard undergradu- ate physics and mathematics courses, as well as the material contained in the first paper in this series. Having studied the material in the “Further Reading" sections of [40] would be ideal, but the material in this series of papers is intended to be self-contained, and familiarity with the first paper will suffice.
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    Note on a NAHE Variation
    (2010-07-09T15:06:42Z) Greenwald, Jared.; Pechan, Kristen.; Renner, Timothy, 1984-; Ali, Tibra; Cleaver, Gerald B.
    We present a variation of the NAHE-basis for free fermionic heterotic string mod- els. By rotating some of boundary conditions of the NAHE periodic/anti-periodic fermions {ym, ym, wm, wm,}, for m = 1 to 6, associated with the six compact dimen- sions of a bosonic lattice/orbifold model, we show an additional method for enhancing the standard NAHE gauge group of SO(10) back to E6. This rotation transforms (SO(10) ⊗ SO(6)3)rmobs ⊗ (E8)hid into (E6 ⊗ U(1)5)obs ⊗ SO(22)hid. When SO(10) is enhanced to E6 in this manner, the ith MSSM matter generation in the SO(10) 16i rep, originating in twisted basis vector bi, recombines with both its associated untwisted MSSM Higgs in a 10i rep and an untwisted non-Abelian singlet φi, to form a 27i rep of E6. Beginning instead with the E6 model, the inverse transformation of the fermion boundary conditions corresponds to partial GUT breaking via boundary rotation. Correspondence between free fermionic models with Z2 ⊗Z2 twist (especially of the NAHE class) and orbifold models with a similar twist has received further attention recently. Our NAHE variation also involves a Z2 ⊗ Z2 twist and offers additional understanding regarding the free fermion/orbifold correspondence. Further, models based on this NAHE variation offer some different phenomenological features compared to NAHE-based models. In particular, the more compact Z2 ⊗ Z2 twist of the NAHE variation offers a range of mirror models not possible from NAHE-based models.
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    Charging and Growth of Fractal Dust Grains
    (IEEE Transactions on Plasma Science, 2008-02) Matthews, Lorin Swint.; Hyde, Truell Wayne.
    The structure and evolution of aggregate grains formed within a plasma environment are dependent on the charge acquired by the micron-sized dust grains during the coagulation process. The manner in which the charge is arranged on developing irregular structures can affect the fractal dimension of aggregates formed during collisions, which, in turn, influences the coagulation rate and size evolution of the dust within the plasma cloud. This paper presents preliminary models for the charge and size evolution of fractal aggregates immersed in a plasma environment calculated using a modification to the orbital motion-limited (OML) theory. Primary electron and ion currents that are incident on points on the aggregate surface are determined using a line-of-sight (LOS) approximation: only those electron or ion trajectories that are not blocked by another grain within the aggregate contribute to the charging current. Using a self-consistent iterative approach, the equilibrium charge and dipole moment are calculated for the dust aggregate. The charges are then used to develop a heuristic charging scheme, which can be implemented in coagulation models. While most coagulation heories assume that it is difficult for like-charged grains to oagulate, the OML_LOS approximation indicates that the electric potentials of aggregate structures are often reduced enough to allow significant coagulation to occur.