F-enomenology

The advantages of Flipped SU(5) over conventional Supersymmetric GUTs, like SU(5), are discussed. Recent values of the strong coupling at M_Z, sin-squared theta-Weinberg, g-2 of the muon, and the lower limit on the proton lifetime for the (K+, anti-neutrino) mode point directly to Flipped SU(5) as the simplest way to avoid potential pitfalls. It is shown that "F(lipped)-enomenology" accomodates easily all presently available low-energy data, favoring a rather "light" supersymmetric spectrum while yielding the right amount of Cold Dark Matter and a proton lifetime in the ((e+/muon+), pi-zero) mode which is beyond the present experimental limit yet still possibly accessible to a further round of experiments.Comment: 22 pages; 3 figures and 2 diagrams prepared with feynmf.mf & feynmf.sty; Invited talk given at: 1st Intl. Conf. on String Phenomenology, Oxford, England, July 6-11, 2002, -and- NeSS 2002, Washington D.C., USA, September 19-21, 200

Supercriticality of a Class of Critical String Cosmological Solutions

For a class of Friedmann-Robertson-Walker type string solutions with compact hyperbolic spatial slices formulated in critical dimension, we find the world sheet conformal field theory which involves the linear dilaton and Wess-Zumino-Witten type model with the compact hyperbolic target space. By analyzing the infrared spectrum, we conclude that the theory is actually supercritical due to the modular invariance of string theory. Thus, taking into account previous results, we conclude that all the simple nontrivial string cosmological solutions are supercritical. A possible explanation of why we are living in D=4 is provided. The interesting relation of this background with the Supercritical String Cosmology (SSC) is pointed out

The march towards no-scale supergravity

The different steps that led us to the discovery of {\em no-scale supergravity} are discussed from a very personal point of view. No-scale supergravity has been heralded as the most promising effective theory that describes physics below the Planck scale. In its string-derived form it holds the potential for a Dynamical Determination Of Everything (DDOE

Natural Inflation with Natural Trans-Planckian Axion Decay Constant from Anomalous U(1)XU(1)_X

We propose a natural inflation model driven by an imaginary or axionic component of a K\"ahler modulus in string-inspired supergravity. The shift symmetry of the axion is gauged under an anomalous $U(1)_X$ symmetry, which leads to a modulus-dependent Fayet-Iliopoulos (FI) term. The matter fields are stabilized by F-terms, and the real component of the modulus is stabilized by the $U(1)_X$ D-term, while its axion remains light. Therefore, the masses of real and imaginary components of the modulus are separated at different scales. The scalar potential for natural inflation is realized by the superpotential from the non-perturbative effects. The trans-Planckian axion decay constant, which is needed to fit with BICEP2 observations, can be obtained naturally in this model.Comment: 14 pages, no figure, references added, version published in JHE

Aligned Natural Inflation and Moduli Stabilization from Anomalous U(1)U(1) Gauge Symmetries

To obtain natural inflation with large tensor-to-scalar ratio in string framework, we need a special moduli stabilization mechanism which can separate the masses of real and imaginary components of K\"ahler moduli at different scales, and achieve a trans-Planckian axion decay constant from sub-Planckian axion decay constants. In this work, we stabilize the matter fields by F-terms and the real components of K\"ahler moduli by D-terms of two anomalous $U(1)_X\times U(1)_A$ symmetries strongly at high scales, while the corresponding axions remain light due to their independence on the Fayet-Iliopoulos (FI) term in moduli stabilization. The racetrack-type axion superpotential is obtained from gaugino condensations of the hidden gauge symmetries $SU(n)\times SU(m)$ with massive matter fields in the bi-fundamental respresentations. The axion alignment via Kim-Nilles-Pelroso (KNP) mechanism corresponds to an approximate $S_2$ exchange symmetry of two K\"ahler moduli in our model, and a slightly $S_2$ symmetry breaking leads to the natural inflation with super-Planckian decay constant.Comment: 17 pages, no figur

Helical Phase Inflation

We show that the quadratic inflation can be realized by the phase of a complex field with helicoid potential. Remarkably, this helicoid potential can be simply realized in minimal supergravity. The global $U(1)$ symmetry of the K\"ahler potential introduces a flat direction and evades the $\eta$ problem automatically. So such inflation is technically natural. The phase excursion is super-Planckian as required by the Lyth bound, while the norm of the complex field can be suppressed in the sub-Planckian region. This model resolves the ultraviolet sensitive problem of the large field inflation, besides, it also provides a new type of monodromy inflation in supersymmetric field theory with consistent field stabilization.Comment: 4 pages+references, 2 figures, phase monodromy in supersymmetric field theory is adde

Helical Phase Inflation via Non-Geometric Flux Compactifications: from Natural to Starobinsky-like Inflation

We show that a new class of helical phase inflation models can be simply realized in minimal supergravity, wherein the inflaton is the phase component of a complex field and its potential admits a deformed helicoid structure. We find a new unique complex-valued index $\chi$ that characterizes almost the entire region of the $n_s-r$ plane favored by new Planck observations. Continuously varying the index $\chi$, predictions interpolate from quadratic/natural inflation parameterized by a phase/axion decay constant to Starobinsky-like inflation parameterized by the $\alpha$-parameter. We demonstrate that the simple supergravity construction realizing Starobinsky-like inflation can be obtained from a more microscopic model by integrating out heavy fields, and that the flat phase direction for slow-roll inflation is protected by a mildly broken global $U(1)$ symmetry. %, which is mildly broken at the inflation energy scale. We study the geometrical origin of the index $\chi$, and find that it corresponds to a linear constraint relating \kah moduli. We argue that such a linear constraint is a natural result of moduli stabilization in Type \MyRoman{2} orientifold compactifications on Calabi-Yau threefolds with geometric and non-geometric fluxes. Possible choices for the index $\chi$ are discrete points on the complex plane that relate to the distribution of supersymmetric Minkowski vacua on moduli space. More precise observations of the inflationary epoch in the future may provide a better estimation of the index $\chi$. Since $\chi$ is determined by the fluxes and vacuum expectation values of complex structure moduli, such observations would characterize the geometry of the internal space as well.Comment: 26 pages, 4 figures; 4+1 figure, discussion on several energy scales added, references added, to appear in JHE

A No-Scale Framework for Sub-Planckian Physics

We propose a minimal model framework for physics below the Planck scale with the following features: (i) it is based on no-scale supergravity, as favoured in many string compactifications, (ii) it incorporates Starobinsky-like inflation, and hence is compatible with constraints from the Planck satellite, (iii) the inflaton may be identified with a singlet field in a see-saw model for neutrino masses, providing an efficient scenario for reheating and leptogenesis, (iv) supersymmetry breaking occurs with an arbitrary scale and a cosmological constant that vanishes before radiative corrections, (v) regions of the model parameter space are compatible with all LHC, Higgs and dark matter constraints.Comment: 6 pages, 2 figures, some minor corrections and additions. Final versio