7,630 research outputs found
Grand unification and enhanced quantum gravitational effects
In grand unified theories with large numbers of fields, renormalization
effects significantly modify the scale at which quantum gravity becomes strong.
This in turn can modify the boundary conditions for coupling constant
unification, if higher dimensional operators induced by gravity are taken into
consideration. We show that the generic size of these effects from gravity can
be larger than the two-loop corrections typically considered in renormalization
group analyses of unification. In some cases, gravitational effects of modest
size can render unification impossible.Comment: 4 pages, 1 figure, revtex; minor changes in v2 (version published in
Phys. Rev. Lett.
Quantum gravity at a TeV and the renormalization of Newton's constant
We examine whether renormalization effects can cause Newton¿s constant to change dramatically with energy, perhaps even reducing the scale of quantum gravity to the TeV region without the introduction of extra dimensions. We examine a model that realizes this possibility and describe experimental signatures from the production of small black holes
Quantum Gravitational Effects and Grand Unification
In grand unified theories with large numbers of fields, renormalization
effects significantly modify the scale at which quantum gravity becomes strong.
This in turn can modify the boundary conditions for coupling constant
unification, if higher dimensional operators induced by gravity are taken into
consideration. We show that the generic size of, and the uncertainty in, these
effects from gravity can be larger than the two-loop corrections typically
considered in renormalization group analyses of unification. In some cases,
gravitational effects of modest size can render unification impossible.Comment: 3 pages, to appear in the proceedings of 16th International
Conference on Supersymmetry and Unification of Fundamental Interactions
(SUSY08), Seoul, Korea, June 16-21 200
Grand unification through gravitational effects
We systematically study the unification of gauge couplings in the presence of
(one or more) effective dimension-5 operators cHGG/4MPl, induced into the grand
unified theory by gravitational interactions at the Planck scale MPl. These
operators alter the usual condition for gauge coupling unification, which can,
depending on the Higgs content H and vacuum expectation value, result in
unification at scales MX significantly different than naively expected. We find
non-supersymmetric models of SU(5) and SO(10) unification, with natural Wilson
coefficients c, that easily satisfy the constraints from proton decay.
Furthermore, gauge coupling unification at scales as high as the Planck scale
seems feasible, possibly hinting at simultaneous unification of gauge and
gravitational interactions. In the Appendix we work out the group theoretical
aspects of this scenario for SU(5) and SO(10) unified groups in detail; this
material is also relevant in the analysis of non-universal gaugino masses
obtained from supergravity.Comment: 27 pages, 5 figures, 8 tables, 1 appendix, revtex; v2: introduction
and conclusion expanded, references added, minor changes, version published
in PR
Unitarity and the Hilbert space of quantum gravity
Under the premises that physics is unitary and black hole evaporation is
complete (no remnants, no topology change), there must exist a one-to-one
correspondence between states on future null and timelike infinity and on any
earlier spacelike Cauchy surface (e.g., slices preceding the formation of the
hole). We show that these requirements exclude a large set of semiclassical
spacetime configurations from the Hilbert space of quantum gravity. In
particular, the highest entropy configurations, which account for almost all of
the volume of semiclassical phase space, would not have quantum counterparts,
i.e. would not correspond to allowed states in a quantum theory of gravity.Comment: 7 pages, 3 figures, revtex; minor changes in v2 (version published in
Class. Quant. Grav.
The Dynamics of Students' Behaviors and Reasoning during Collaborative Physics Tutorial Sessions
We investigate the dynamics of student behaviors (posture, gesture, vocal
register, visual focus) and the substance of their reasoning during
collaborative work on inquiry-based physics tutorials. Scherr has characterized
student activity during tutorials as observable clusters of behaviors separated
by sharp transitions, and has argued that these behavioral modes reflect
students' epistemological framing of what they are doing, i.e., their sense of
what is taking place with respect to knowledge. We analyze students' verbal
reasoning during several tutorial sessions using the framework of Russ, and
find a strong correlation between certain behavioral modes and the scientific
quality of students' explanations. We suggest that this is due to a dynamic
coupling of how students behave, how they frame an activity, and how they
reason during that activity. This analysis supports the earlier claims of a
dynamic between behavior and epistemology. We discuss implications for research
and instruction.Comment: 4 pages, PERC 200
Ultrasonic NDE Techniques and the Effects of Flaws on Mechanical Performance in Multi-Directionally Reinforced Textile Composites
Developmental efforts in composite technology have included a wide variety of secondary and primary structure in industries ranging from sporting goods to high performance aircraft. In addition to potentially significant weight savings, composites offer the potential benefits of increased fatigue life, corrosion resistance, and acquisition or life-cycle cost savings. Conventional two-dimensional composites, however, have poor interlaminar strengths and are susceptible to damage
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