physical review letter string thoery

physical review letter string thoery - 01(2007 PHYSICAL...

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Falsifying Models of New Physics via WW Scattering Jacques Distler, 1 Benjamin Grinstein, 2 Rafael A. Porto, 3 and Ira Z. Rothstein 3 1 University of Texas, Dept. of Physics, Austin, Texas 78712, USA 2 University of California, San Diego, Dept. of Physics, La Jolla, California 92093-0319, USA 3 Carnegie-Mellon University, Dept. of Physics, Pittsburgh, Pennsylvania 15213, USA (Received 2 October 2006; published 22 January 2007) We show that the coefFcients of operators in the electroweak chiral Lagrangian can be bounded if the underlying theory obeys the usual assumptions of Lorentz invariance, analyticity, unitarity, and crossing to arbitrarily short distances. Violations of these bounds can be explained by either the existence of new physics below the naive cutoff of the effective theory, or by the breakdown of one of these assumptions in the short distance theory. As a corollary, if no light resonances are found, then a measured violation of the bound would falsify generic models of string theory. DOI: 10.1103/PhysRevLett.98.041601 PACS numbers: 12.15.Ji, 11.25.Wx, 11.55. ÿ m, 12.60.±r The standard model (SM) is only an effective Feld theory, a good approximation only at energies below some scale ± . This scale, however, is still undetermined. If, as naturalness arguments indicate, new physics is re- quired to explain the relative smallness of the weak to Planck scale ratio, then we would expect the theory to break down at energies of about 1 TeV. However, even if naturalness arguments fail, we still know that the SM, augmented by Einstein gravity, must break down at the scale of quantum gravity, where predictive power is lost. In searching for low-energy effects of the physics which underlies the SM, it is prudent to take the model indepen- dent approach of adding operators of dimension higher than four to the SM Lagrangian and parameterizing the new physics by their coefFcients. Dimensional analysis dictates that these coefFcients contain inverse powers of ± , so the precision with which we must extract them grows with the scale of new physics. This decoupling phenomena makes falsifying theories of the underlying short distance interactions [the ultraviolet (UV))] extremely difFcult. Indeed, if the scale of quantum gravity is as high as the Planck scale, it becomes interesting to ask the question as to whether or not the theory is, even in principle, falsiFable. One possibility is that the mathematical structure leads to unique low-energy predictions. However, in the case of string theory, recent progress seems to indicate that this is not a likely scenario. Another possibility is that there are low-energy, non-Planck suppressed, consequences of some underlying symmetries. Symmetries link the UV and the infrared (IR) by distinguishing between universality classes. However, string theory does not seem to have any problems generating the low-energy symmetries man- ifested at energies presently explored. Indeed, given the enormous number of string vacua, it may be that string theory can accommodate whatever new physics is found at the TeV scale by the Large Hadron Collider (LHC).
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This note was uploaded on 06/02/2008 for the course PHYS 414 taught by Professor White during the Spring '08 term at Texas A&M.

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physical review letter string thoery - 01(2007 PHYSICAL...

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