14760942
A realistic unified gauge coupling from the micro-landscape of orbifold GUTs
Abstract We consider 5-dimensional supersymmetric field theories where supersymmetry is broken by the Scherk–Schwarz mechanism (or, equivalently, by the F-term VEV of the radion). In such models, the radion effective potential is calculable in terms of the 5d gauge coupling, the UV cutoff of the 5d field theory, and the field content. We provide simple, explicit formulae for the leading part of the two-loop effective potential. Our analysis applies in particular to 5d orbifold GUTs motivated by heterotic orbifold models. We focus on potentially realistic models of this type and make the additional assumption that the UV cutoff scale is identical with the strong-coupling scale of the 5d gauge theory. Given our stabilization mechanism, the 5d radius is now fixed in terms of the 5d gauge coupling and the field content of the model. This implies a prediction for the effective 4d gauge coupling only in terms of the field content of the model. Given the ‘micro-landscape’ provided by the different possible distributions of Standard Model fields between bulk and branes, we find a subset of models with a realistic unified gauge coupling. We also discuss two possibilities for the ‘uplifting’ of our SUSY-breaking AdS vacua: One is based on the possible presence of a weak warping, the other appeals to F-terms in an extra brane-localized SUSY-breaking sector.
119272291
Flavorful hybrid anomaly-gravity mediation
We consider supersymmetric models where anomaly and gravity mediation give comparable contributions to the soft terms and discuss how this can be realized in a five-dimensional brane world. The gaugino mass pattern of anomaly mediation is preserved in such a hybrid setup. The flavorful gravity-mediated contribution cures the tachyonic slepton problem of anomaly mediation. The supersymmetric flavor puzzle is solved by alignment. We explicitly show how a working flavor-tachyon link can be realized with Abelian flavor symmetries and give the characteristic signatures of the framework, including O(1) slepton mass splittings between different generations and between doublets and singlets. This provides opportunities for same flavor dilepton edge measurements with missing energy at the Large Hadron Collider (LHC). Rare lepton decay rates could be close to their current experimental limit. Compared to pure gravity mediation, the hybrid model is advantageous because it features a heavy gravitino which can avoid the cosmological gravitino problem of gravity-mediated models combined with leptogenesis.
8572469
Constructing de Sitter vacua in no-scale string models without uplifting
We develop a method for constructing metastable de Sitter vacua in N = 1 supergravity models describing the no-scale volume moduli sector of Calabi-Yau string compactifications. We consider both heterotic and orientifold models. Our main guideline is the necessary condition for the existence of metastable vacua coming from the Goldstino multiplet, which constrains the allowed scalar geometries and supersymmetry-breaking directions. In the simplest non-trivial case where the volume is controlled by two moduli, this condition simplifies and turns out to be fully characterised by the intersection numbers of the Calabi-Yau manifold. We analyse this case in detail and show that once the metastability condition is satisfied it is possible to reconstruct in a systematic way the local form of the superpotential that is needed to stabilise all the fields. We apply then this procedure to construct some examples of models where the superpotential takes a realistic form allowed by flux backgrounds and gaugino condensation effects, for which a viable vacuum arises without the need of invoking corrections to the Kahler potential breaking the no-scale property or uplifting terms. We finally discuss the prospects of constructing potentially realistic models along these lines.
122665147
De Sitter vacua and inflation in no-scale string models
This thesis studies the question of how de Sitter vacua and slow-roll inflation may be realized in string-motivated models. More specifically, we consider 4d N = 1 supergravity theories (without vector multiplets) with Kahler potentials which are ‘no-scale’ at leading order. Such theories frequently arise in the moduli sector of string compactifications. We discuss a condition on the scalar geometry (defined by the Kahler potential) and on the direction of supersymmetry breaking in the scalar manifold, which has to be met in order for the average of the masses of the sGoldstinos to be positive, and hence for metastable vacua to be possible. This condition also turns out to be necessary for the existence of trajectories admitting slow-roll inflation. Its implications for certain scalar manifolds which arise from Calabi-Yau string compactifications are discussed. In particular, for two-moduli models arising from compactifications of heteroticand type IIB string theory, a simple criterion on the intersection numbers needs to be satisfied for possible de Sitter phases to exist. In addition, we show that subleading corrections breaking the no-scale property may allow the condition on the scalar geometry to be fulfilled, even when it is violated at leading order. Finally, we develop a procedure to construct superpotentials for a given viable Kahler potential, such that the scalar potential has a realistic local minimum. We propose two-moduli models, with superpotentials which could arise from flux backgrounds and non-perturbative effects, which have a viable vacuum without employing subleading corrections or an uplifting sector.
15184738
Constraints on modular inflation in supergravity and string theory
We perform a general algebraic analysis on the possibility of realising slow-roll inflation in the moduli sector of string models. This problem turns out to be very closely related to the characterisation of models admitting metastable vacua with non-negative cosmological constant. In fact, we show that the condition for the existence of viable inflationary trajectories is a deformation of the condition for the existence of metastable de Sitter vacua. This condition depends on the ratio between the scale of inflation and the gravitino mass and becomes stronger as this parameter grows. After performing a general study within arbitrary supergravity models, we analyse the implications of our results in several examples. More concretely, in the case of heterotic and orientifold string compactifications on a Calabi-Yau in the large volume limit we show that there may exist fully viable models, allowing both for inflation and stabilisation. Additionally, we show that subleading corrections breaking the no-scale property shared by these models always allow for slow-roll inflation but with an inflationary scale suppressed with respect to the gravitino scale. A scale of inflation larger than the gravitino scale can also be achieved under more restrictive circumstances and only for certain types of compactifications.
115171499
\theta^PMNS_13 = \theta_C / \sqrt2 from GUTs
Abstract The recent observations of the leptonic mixing angle θ 13 PMNS are consistent with θ 13 PMNS = θ C / 2 (with θ C being the Cabibbo angle θ 12 CKM ). We discuss how this relation can emerge in Grand Unified Theories (GUTs) via charged lepton corrections. The key ingredient is that in GUTs the down-type quark Yukawa matrix and the charged lepton Yukawa matrix are generated from the same set of GUT operators, which implies that the resulting entries are linked and differ only by group-theoretical Clebsch factors. This allows a link θ 12 e ≈ θ C to be established, which can induce θ 13 PMNS ≈ θ C / 2 provided that the 1–3 mixing in the neutrino mass matrix is much smaller than θ C . We find simple conditions under which θ 13 PMNS ≈ θ C / 2 can arise via this link in SU(5) GUTs and Pati–Salam models. We also discuss possible corrections to the exact relation. Using lepton mixing sum rules different neutrino mixing patterns can be distinguished by their predictions for the Dirac CP phase δ PMNS .
120158410
Dynamic polarization in the Coulomb breakup of loosely bound 17F
Abstract Angular distributions of the Coulomb breakup of radioactive 17 F were measured by impinging a 10 MeV/nucleon beam on 208 Pb and on 58 Ni to study the dynamic polarization effects. The breakup products, oxygen and a proton, were detected in coincidence. First-order perturbation theory significantly overpredicts the breakup cross section for the 208 Pb target. Dynamical calculations with a dynamic polarization as the leading order correction were performed. The calculations reproduce the data for 17 F on 58 Ni but overpredict the breakup of 17 F on 208 Pb by a factor of two at forward angles.
121130051
Recent results at HRIBF using neutron-rich radioactive ion beams
Several recent experiments at the Holifield Radioactive Ion Beam Facility using neutron-rich radioactive ion beams (RIBs) are briefly described. These experiments contribute significantly to the growing list of techniques currently used with RIBs. Recent fusion-evaporation cross-section measurements below the Coulomb barrier for the 132Sn + 64Ni reaction suggest enhancement as compared to 124Sn + 64Ni reaction. These studies are being expanded to include reactions with 134Sn. The g factor of the first 2+ state in 132Te has been measured to be 0.35(5) through the recoil-in-vacuum technique. Angular distributions have been measured in the reaction 13C(134Te,135Te)12C at 550 MeV and used to suggest the spin and parity of a new 2109 keV state in 135Te as , suggesting a single-particle configuration of . Decay spectroscopy may be further enhanced using a ranging-out technique to reduce the isobaric impurity of neutron-rich beams.
123674609
Band Structure in 79Y and the Question of T=0 Pairing
Excited states in the N = Z+1 nucleus Y-79 Were identified using the reaction Si-28(Fe-54, p2n)Y-79 at a 200 MeV beam energy and an experimental set up consisting of an array of Ge detectors and the Recoil Mass Spectrometer at Oak Ridge National Laboratory. With the help of additional gamma-gamma coincidence data obtained with Gammasphere, these gamma-rays were found to form a strongly-coupled rotational band with rigid-rotor-like behavior. Results of conventional Nilsson-Strutinsky cranked shell model calculations, which predict a deformation of beta(2)similar to 0.4, are in excellent agreement with the properties of this band. Similar calculations for the neighboring N = Z and N = Z + 1 nuclei are also in good agreement with experimental data. This suggests that the presence of the putative T = 0 neutron-proton pairing does not significantly affect such simple observables as the moments of inertia of these bands at low spins. (Less)
119853543
Systematics of isomeric configurations in N=77 odd-Z isotones near the proton drip line
The systematics of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{s}_{1/2}$ isomeric configurations was studied for the odd-Z $N=77$ isotones near the proton drip line. The isomeric decays in $^{140}\mathrm{Eu}$, $^{142}\mathrm{Tb}$, $^{144}\mathrm{Ho}$, and $^{146}\mathrm{Tm}$ were measured by means of x-ray, \ensuremath{\gamma}-ray, and charged particle spectroscopy at the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility (ORNL). The spin and parity of ${I}^{\ensuremath{\pi}}={8}^{+}$ and ${5}^{\ensuremath{-}}$ were deduced for the isomers in $^{140}\mathrm{Eu}$ and $^{142}\mathrm{Tb}$. New decay schemes were established, and the half-lives of the ${8}^{+}$ isomers were measured to be 302(4) ns for $^{140m2}\mathrm{Eu}$ and 25(1) \ensuremath{\mu}s for $^{142m2}\mathrm{Tb}$. No evidence for the expected ${1}^{+}$ ground-state was found in the $^{144}\mathrm{Ho}$ decay data. The proton-emission from $^{146}\mathrm{Tm}$ was restudied. Five proton transitions were assigned to two proton-emitting states. The half-lives of 198(3) ms and 68(3) ms and the spin and parity values of ${I}^{\ensuremath{\pi}}={10}^{+}$ and ${5}^{\ensuremath{-}}$ were established for $^{146m}\mathrm{Tm}$ and $^{146\mathrm{gs}}\mathrm{Tm}$, respectively. For the first time for an odd-odd nucleus, the interpretation of the observed decay properties and structure of the proton-emitting states was made by accounting for deformation and proton and neutron coupling to the core excitations. A complex wave-function structure was obtained, with dominating components of $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ for the ${10}^{+}$ isomer and $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{s}_{1/2}$ for the ${5}^{\ensuremath{-}}$ ground state.
33952822
New half-lives of r-process Zn and Ga isotopes measured with electromagnetic separation.
The β decays of neutron-rich nuclei near the doubly magic (78)Ni were studied at the Holifield Radioactive Ion Beam Facility using an electromagnetic isobar separator. The half-lives of (82)Zn (228±10  ms), (83)Zn (117±20  ms), and (85)Ga (93±7  ms) were determined for the first time. These half-lives were found to be very different from the predictions of the global model used in astrophysical simulations. A new calculation was developed using the density functional model, which properly reproduced the new experimental values. The robustness of the new model in the (78)Ni region allowed us to extrapolate data for more neutron-rich isotopes. The revised analysis of the rapid neutron capture process in low entropy environments with our new set of measured and calculated half-lives shows a significant redistribution of predicted isobaric abundances strengthening the yield of A>140 nuclei.