Actual problems of gravitation
 
 
 
 
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There are at least two seemingly fundamental energy scales in nature, the electroweak scale and the Planck scale GeV, where gravity becomes as strong as the gauge interactions. Over the last two decades, explaining the smallness and radiative stability of the hierarchy has been one of the greatest driving forces behind the construction of theories beyond the Standard Model (SM) . While many di.erent specific proposals for weak and Planck scale physics have been made, there is a commonly held picture of the basic structure of physics beyond the SM. A new e.ective field theory (e.g. a softly broken supersymmetric theory or technicolor) is revealed at the weak scale, stabilizing and perhaps explaining the origin of the hierarchy. On the other hand, the physics responsible for making a sensible quantum theory of gravity is revealed only at the Planck scale. The desert between the weak and Planck scales could itself be populated with towers of new effective field theories which can play a number of roles, such as triggering dynamical symmetry breakings or explaining the pattern of fermion masses and mixings. In this picture, the experimental investigation of weak scale energies is quite exciting, as it is guaranteed to reveal the true mechanism of electroweak symmetry breaking and stabilization of the hierarchy. One can also hope that a detailed measurement of low energy parameters can give valuable clues to the structure of e.ective field theories at higher energies, perhaps even approaching the Planck scale. Nevertheless, it is fair to say that in this paradigm, the thorough exploration of the weak scale will never give a direct experimental handle on strong gravitational physics. It is remarkable that such rich theoretical structures have been built on the assumption of the existence of two disparate fundamental energy scales, and . However, there is an important di.erence between these scales. While electroweak interactions have been probed at distances , gravitational forces have not remotely been probed at distances : gravity has only been accurately measured in the ~1cm range. Our interpretation of as a fundamental energy scale (where gravitational interactions become strong) is then based on the assumption that gravity is unmodified over the 33 orders of magnitude between where it is measured at a ~1 cm down to the Planck length cm. Given the crucial way in which the fundamental role attributed to affects our current thinking, it is worthwhile questioning this extrapolation and seeking new alternatives to the standard picture of physics beyond the SM. In fact, given that the fundamental nature of the weak scale is an ex- perimental certainty, we wish to take the philosophy that mEW is the only fundamental short distance scale in nature, even setting the scale for the strength of the gravitational interaction.

The major part of the content is taken from:
N. Arkani-Hamed, S. Dimopoulos, and G. Dvali, "The Hierarchy Problem and New Dimensions at a Millimeter," Phys. Lett. B 429, 263 (1998)

 

 
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