Monday, May 10, 2010


The most interesting paper today n arxiv hep_th is very probably this: Uber-naturalness: unexpectedly light scalars from supersymmetric extra dimensions

This is the abstract:

Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M_KK, in extra-dimensional models, or the gravitino mass, M_3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M_g, (e.g. the string scale, M_s, in string theory) is of order the Planck mass, M_p = 10^18 GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M_g and M_p is parameterized by the (large) size of the extra dimensional volume, V (in string units), according to M_p: M_g: M_KK: M_3/2 = 1: V^{-1/2}: V^{-2/3}: V^{-1}. We find that the generic size of quantum corrections to masses is of the order of M_KK M_3/2 / M_p ~ M_p / V^{5/3}. The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M_V ~ M_p/V^{3/2} << M_3/2 << M_KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation

One of the good things of this kind of theories is that a combination of supersymmetry and large extra dimensions allow that the gravitino wouldn't be the LSP in the kind of theories where it would usually be it. That is good if the controversial results claiming the existence of dark matter of 10 GeV are confirmed. As far as I know the gavitino couldn't be the particle responsible for that kind of DM. That's bad because the gravitino is the LSP in the Vafa F-theory GUTs. But if the idea of this paper can be translated to F-theory (which after all shares some of the characteristics of the LV theories disused in this paper) it could give them the flexibility to not be immediately ruled out if the DM experiments confirm the discovering.

Obviously the interest of the paper goes beyond that particular purpose of my own concern. It is a theoretic paper of wide interest and not a phenomenologistic paper devoted to a narrow particular subject. Anyway, it is clear that if someone wants to properly appreciate this paper beyond string theory he needs a good familiarity with supersymmetry, as explained in, for example, the book of the previous entry and cosmological issues of dark matter and inflation.

Update: A litle of meditation shows an obvious obstacle to use plainly this constructions inf F-theory, The idea of this paper relies in a variant of gravity mediated supersymmetry breaking. In F-theory supersymmetry is broken bye a variant of the guidice-massiero mechanism that belongs to gauge mediated supersymmetry breaking. Worse, the very idea of F-theory GUTS relies in the gravity decoupling so it seems hard to incorporate this idea in an straightforward way. Ok, I never have claimed to be at all an expert in F-theory or phenomenology. But I fell s if my understanding of this topics is growing fast, maybe in a few centuries I could publish something worthfull ;).

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