Remarks on Limits on String Scale from Proton Decay and Low-Energy amplitudes in Braneworld Scenario

We discuss IR limit of four-fermion scattering amplitudes in braneworld models including intersecting-branes and SUSY SU(5) GUT version of it. With certain compactification where instanton effect is negligible, grand unification condition in D6-D6 intersecting-branes scenario subject to experimental constraint on proton decay provides possibility for upper limit on the string scale, $M_S$, through relationship between the string coupling, $g_s$, and the string scale. We discuss how IR divergence is related to number of twisted fields we have to introduce into intersection region and how it can change IR behaviour of tree-level amplitudes in various intersecting-branes models. Using number of twisted fields, we identify some intersecting-branes models whose tree-level amplitudes are purely stringy in nature and automatically proportional to $g_s/M^2_{S}$ at low energy. They are consequently suppressed by the string scale. For comparison, we also derive limit on the lower bound of the string scale from experimental constraint on proton decay induced from purely stringy contribution in the coincident-branes model, the limit is about $10^5$ TeV.Comment: 14 page

Rampant Decay, February 22, 2013

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Rampant Decay, June 21, 2013

https://digitalcommons.ric.edu/as220_performance_space/1022/thumbnail.jp

Charged Mesons

2 j 8ß f 2 P m 2 ` m P ` 1 \Gamma m 2 ` m 2 P ' 2 [1 +O(ff)] : Radiative corrections include inner bremsstrahlung, which is independent of the structure of the meson [1--3], and also a structure-dependent term [4,5]. After radiative corrections are made, there are ambiguities in extracting f P from experimental measurements. In fact, the definition of f P is no longer unique. It is desirable to define f P such that it depends only on the properties of the pseudoscalar meson, not on the final decay products. The short-distance corrections to the fundamental electroweak constants like G F jV qq 0 j should be separate