Two-loop vacuum amplitude in four-dimensional heterotic string models |
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Affiliation: | 1. International Centre for Theoretical Physics, I-34100 Trieste, Italy;1. Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Trieste, Trieste, Italy;2. International School for Advanced Studies, I-34014 Trieste, Italy |
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Abstract: | The two-loop measure of four-dimensional heterotic strings with N=4, 2 and 1 space-time supersymmetry is explicitly calculated. It is shown that the cosmological constants of these models at two loops are zero. |
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