Towards a nonsupersymmetric string phenomenology

Abstract

Over the past three decades, considerable effort has been devoted to studying the rich and diverse phenomenologies of heterotic strings exhibiting spacetime supersymmetry. Unfortunately, during this same period, there has been relatively little work studying the phenomenologies associated with their non-supersymmetric counterparts. The primary reason for this relative lack of attention is the fact that strings without spacetime supersymmetry are generally unstable, exhibiting large one-loop dilaton tadpoles. In this paper, we demonstrate that this hurdle can be overcome in a class of tachyon-free four-dimensional string models realized through coordinate-dependent compactifications. Moreover, as we shall see, it is possible to construct models in this class whose low-lying states resemble the Standard Model (or even potential unified extensions thereof) -all without any light superpartners, and indeed without supersymmetry at any energy scale. The existence of such models thus opens the door to general studies of non-supersymmetric string phenomenology, and in this paper we proceed to discuss a variety of theoretical and phenomenological issues associated with such non-supersymmetric strings. On the theoretical side, we discuss the finiteness properties of such strings, the general characteristics of their mass spectra, the magnitude and behavior of their one-loop cosmological constants, and their interpolation properties. By contrast, on the phenomenological side, the properties we discuss are more model-specific and include their construction techniques, their natural energy scales, their particle and charge assignments, and the magnitudes of their associated Yukawa couplings and scalar masses.

GUT precursors and entwined SUSY: The phenomenology of stable nonsupersymmetric strings

“…[1], we demonstrated how such metastable strings may be constructed within the perturbative heterotic framework. Moreover, as we demonstrated, the low-energy limits of these strings may even resemble the Standard Model or one of its grand-unified extensions [1].…”

“…[1], we demonstrated how such metastable strings may be constructed within the perturbative heterotic framework. Moreover, as we demonstrated, the low-energy limits of these strings may even resemble the Standard Model or one of its grand-unified extensions [1]. This then opens up the possibility of developing a fully nonsupersymmetric string phenomenology-one in which the Standard Model itself is realized directly as the low-energy limit of a nonsupersymmetric string.…”

“…In recent work [1], we advocated a new approach to this problem. Specifically, even though nonsupersymmetric strings are generally unstable, they may nevertheless be metastable-i.e., endowed with lifetimes that are large compared with the age of the universe.…”

“…[1] and undertake such a phenomenological study. Accordingly, the topics discussed in this paper inevitably cover a lot of territory, stretching from the stability of nonsupersymmetric strings and new methods of making sense of large-volume compactifications all the way to the phenomenological implications of nontrivial techniques for breaking GUT's and supersymmetry simultaneously.…”

“…First, in Sec. II, we review our general framework [1] for the construction of nonsupersymmetric heterotic strings with exponentially suppressed one-loop dilaton tadpoles. This is the framework in which all of our subsequent discussion takes place, and we include this short review in order to render this paper self-contained.…”