351 research outputs found
Robustness and Predictivity of 4 TeV Unification
The stability of the predictions of two of the standard model parameters, and , in a TeV unification model is examined. It is concluded that varying the unification scale between TeV and TeV leaves robust all predictions within reasonable bounds. Choosing TeV gives, at lowest order, accurate predictions at . Flavor-changing effects and deviations from precision electroweak data are discussed
Reexamination of relaxation of spins due to a magnetic field gradient: Identity of the Redfield and Torrey theories
There is an extensive literature on magnetic-gradient-induced spin relaxation. Cates, Schaefer, and Happer, in a seminal publication, have solved the problem in the regime where diffusion theory (the Torrey equation) is applicable using an expansion of the density matrix in diffusion equation eigenfunctions and angular momentum tensors. McGregor has solved the problem in the same regime using a slightly more general formulation using the Redfield theory formulated in terms of the autocorrelation function of the fluctuating field seen by the spins and calculating the correlation functions using the diffusion-theory Green's function. The results of both calculations were shown to agree for a special case. In the present work, we show that the eigenfunction expansion of the Torrey equation yields the expansion of the Green's function for the diffusion equation, thus showing the identity of this approach with that of the Redfield theory. The general solution can also be obtained directly from the Torrey equation for the density matrix. Thus, the physical content of the Redfield and Torrey approaches are identical. We then introduce a more general expression for the position autocorrelation function of particles moving in a closed cell, extending the range of applicability of the theory
Fivebranes and 4-manifolds
We describe rules for building 2d theories labeled by 4-manifolds. Using the
proposed dictionary between building blocks of 4-manifolds and 2d N=(0,2)
theories, we obtain a number of results, which include new 3d N=2 theories
T[M_3] associated with rational homology spheres and new results for
Vafa-Witten partition functions on 4-manifolds. In particular, we point out
that the gluing measure for the latter is precisely the superconformal index of
2d (0,2) vector multiplet and relate the basic building blocks with coset
branching functions. We also offer a new look at the fusion of defect lines /
walls, and a physical interpretation of the 4d and 3d Kirby calculus as
dualities of 2d N=(0,2) theories and 3d N=2 theories, respectivelyComment: 81 pages, 18 figures. v2: misprints corrected, clarifications and
references added. v3: additions and corrections about lens space theory,
4-manifold gluing, smooth structure
The Ursinus Weekly, February 18, 1957
Visiting group to complete U.C. evaluation this week • Twenty students enter at mid-year • Men\u27s council hears suggestions • Curtain Club to present The Valiant on Feb. 26 • W.F. Speilman, member of UC maintenance staff, dies • Chest drive dates released • Y association to hear refugees • Senate decides on WSGA revisions • Frosh women\u27s representatives chosen; To be installed on Color Day, Thursday • St. John Terrell addresses Forum on drama history • Peirce - Pauli engagement • Dave Burger made king of annual Lorelei, Fri., Feb. 15 • Selective Service rules published by administration • Snyder receives Ph.D. degree Feb. 9 • S.R.C. discusses mental health • Two UC women attend confab on religious work • Chess Club plays F&M • Editorial: Word of welcome and some comments on evaluation • May Day • Brotherhood Week and the work of the National Conference of Christians and Jews • IRC to hear talk tonight on U.S. and Phillipines • Age of service • Cagers lose to Fords in overtime; Lose to Garnet five Saturday, 84-64 • Ursinus mermaids defeat Drexel Wed. • Belles register two net shutouts • William Yost resigns from court post • Padula stopped as matmen score win over E\u27town, Sat. • Chi Alpha hears Baker, sponsors weekly talks • Newman Club to hear discussion on J.H. Newman • Y heads discuss activities, plans at retreat, Sat. • Pre-med society hears Mercurio; Plans dinner • Fourteen go on mid-year trip to Washington, D.C. • Reed and Barton contest to run through Feb., Mar.https://digitalcommons.ursinus.edu/weekly/1421/thumbnail.jp
Real Special Geometry
We give a coordinate-free description of real manifolds occurring in certain
four dimensional supergravity theories with antisymmetric tensor fields. The
relevance of the linear multiplets in the compactification of string and
five-brane theories is also discussed.Comment: 10 pgs (TeX with Harvmac), CERN-TH.7211/94, UCLA/94/TEP/14,
POLFIS-TH.01/9
Moduli potentials in string compactifications with fluxes: mapping the Discretuum
We find de Sitter and flat space solutions with all moduli stabilized in four
dimensional supergravity theories derived from the heterotic and type II string
theories, and explain how all the previously known obstacles to finding such
solutions can be removed. Further, we argue that if the compact manifold allows
a large enough space of discrete topological choices then it is possible to
tune the parameters of the four dimensional supergravity such that a hierarchy
is created and the solutions lie in the outer region of moduli space in which
the compact volume is large in string units, the string coupling is weak, and
string perturbation theory is valid. We show that at least two light chiral
superfields are required for this scenario to work, however, one field is
sufficient to obtain a minimum with an acceptably small and negative
cosmological constant. We discuss cosmological issues of the scenario and the
possible role of anthropic considerations in choosing the vacuum of the theory.
We conclude that the most likely stable vacuua are in or near the central
region of moduli space where string perturbation theory is not strictly valid,
and that anthropic considerations cannot help much in choosing a vacuum.Comment: 34 pages, no figure
M-Theory Moduli Space and Cosmology
We conduct a systematic search for a viable string/M-theory cosmology,
focusing on cosmologies that include an era of slow-roll inflation, after which
the moduli are stabilized and the Universe is in a state with an acceptably
small cosmological constant. We observe that the duality relations between
different cosmological backgrounds of string/M-theory moduli space are greatly
simplified, and that this simplification leads to a truncated moduli space
within which possible cosmological solutions lie. We review some known
challenges to four dimensional models in the "outer", perturbative, region of
moduli space, and use duality relations to extend them to models of all of the
(compactified) perturbative string theories and 11D supergravity, including
brane world models. We conclude that cosmologies restricted to the outer region
are not viable, and that the most likely region of moduli space in which to
find realistic cosmology is the "central", non-perturbative region, with
coupling and compact volume both of order unity, in string units.Comment: 42 pages, 3 figure
New Sum Rules from Low Energy Compton Scattering on Arbitrary Spin Target
We derive two sum rules by studying the low energy Compton scattering on a
target of arbitrary (nonzero) spin j. In the first sum rule, we consider the
possibility that the intermediate state in the scattering can have spin |j \pm
1| and the same mass as the target. The second sum rule applies if the theory
at hand possesses intermediate narrow resonances with masses different from the
mass of the scatterer. These sum rules are generalizations of the
Gerasimov-Drell-Hearn-Weinberg sum rule. Along with the requirement of tree
level unitarity, they relate different low energy couplings in the theory.
Using these sum rules, we show that in certain cases the gyromagnetic ratio can
differ from the "natural" value g=2, even at tree level, without spoiling
perturbative unitarity. These sum rules can be used as constraints applicable
to all supergravity and higher-spin theories that contain particles charged
under some U(1) gauge field. In particular, applied to four dimensional N=8
supergravity in a spontaneously broken phase, these sum rules suggest that for
the theory to have a good ultraviolet behavior, additional massive states need
to be present, such as those coming from the embedding of the N=8 supergravity
in type II superstring theory. We also discuss the possible implications of the
sum rules for QCD in the large-N_c limit.Comment: 18 pages, v2: discussion on black hole contribution is included,
references added; v3: extended discussion in introduction, version to appear
in JHE
Moduli Stabilisation in Heterotic Models with Standard Embedding
In this note we analyse the issue of moduli stabilisation in 4d models
obtained from heterotic string compactifications on manifolds with SU(3)
structure with standard embedding. In order to deal with tractable models we
first integrate out the massive fields. We argue that one can not only
integrate out the moduli fields, but along the way one has to truncate also the
corresponding matter fields. We show that the effective models obtained in this
way do not have satisfactory solutions. We also look for stabilised vacua which
take into account the presence of the matter fields. We argue that this also
fails due to a no-go theorem for Minkowski vacua in the moduli sector which we
prove in the end. The main ingredient for this no-go theorem is the constraint
on the fluxes which comes from the Bianchi identity.Comment: 20 pages, LaTeX; references adde
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