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.
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 .
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.
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.
122384124
Lifetime Measurements of Normally Deformed and Superdeformed States in 82Sr
Lifetimes of a superdeformed band in Sr-82 were measured with the centroid shift method. The measured average quadrupole moment of this band corresponds to a quadrupole deformation of beta(2) approximate to 0.49, which is slightly smaller than both the theoretical prediction, and the measured deformation of the SD band in the neighboring isotone Zr-84. Lifetimes of high spin states of three normally deformed rotational bands in Sr-82 were also measured with the Doppler shift attenuation method technique. The quadrupole moments of these normally deformed bands show a decrease at the highest spins, supporting the predicted band terminations.
124116361
Excited states in As 82 studied in the decay of Ge 82
The excited states of odd-odd $^{82}\mathrm{As}$ are studied in the $\ensuremath{\beta}$ decay of $^{82}\mathrm{Ge}$. An isotopically pure beam of $^{83}\mathrm{Ga}$ was produced at the Holifield Radioactive Ion Beam Facility using a resonance ionization laser ion source and high-resolution electromagnetic separation. The atoms of $^{82}\mathrm{Ge}$ are created after $\ensuremath{\beta}$-delayed neutron emission in the decay of $^{83}\mathrm{Ga}$. The number of $^{82}\mathrm{Ge}$ atoms is found by normalization to the 1348-keV $\ensuremath{\gamma}$ ray. Detailed analysis of the decay scheme is compared with shell-model calculations with several commonly used $fpg$ shell interactions.
123073592
Identification of Excited States in the Tz=+1/2 Nucleus 75Rb: The Quest for Experimental Signatures of Collective Neutron-proton Correlations
Excited states in the T-z-1/2 nucleus Rb-75 were observed for the first time using the Ca-40(Ca-40,alpha p) reaction at 128 MeV. Identification was achieved using events detected by the Daresbury recoil separator in coincidence with gamma rays detected in the 45 element EUROGAM I Ge-detector array. Threefold events were used to build a decay scheme which consists of two rotational bands observed to I-pi=(45+/2) and I-pi=(33-/2). The positive parity band in Rb-75 behaves similarly to a negative-parity band in Kr-74 and contains a region of alignment at (h) over bar omega approximate to 0.75 MeV. These data, and those of Sr-77, be interpreted by treating protons and neutrons separately in a cranked shell model approach despite a recent suggestion for the presence of T=1 neutron-proton pairing correlations in the neighboring self-conjugate, odd-odd Rb-74 ground state band. Our study suggests that some experimental observables such as the energy levels and moments of inertia, may not be able to differentiate between different T=1 pairing phases in these T-z=1/2 nuclei. (Less)
115767621
Lifetimes of high-spin states in the pii13/2 band of 173Re
Lifetime measurements on the i{sub 13/2} band built on the proton configuration 1/2{sup +}[660] in {sup 173}Re have been carried out by the Doppler-broadened line shape method with the use of the GAMMASPHERE array in an early-implementation arrangement. Lifetimes of the stretched E2 transitions from states of spin 41/2{sup +}{endash}69/2{sup +} in this band were measured, and the transition quadrupole moments calculated from these lifetimes are consistent (average Q{sub t}=8.1{plus_minus}0.5eb) with a large and near-constant deformation ({beta}{sub 2}{approx}0.29) over the frequency range of {h_bar}{omega}=0.29{endash}0.47 MeV. This result attests to the strong deformation-driving effect of the intruder {pi}i{sub 13/2} orbital when it lies just above the Fermi surface. From thin-target measurements, it was possible to add three new levels to this band and to determine that the experimental aligned angular momenta gradually evolve over a large frequency range and level off with a total gain characteristic of alignment by i{sub 13/2} neutrons. Calculations carried out for diabatic configurations give a satisfactory accounting of the alignment gain. However, because of the large interaction between crossing bands, a more meaningful description of the deformation pattern in this band was achieved through calculations of the spin-adiabatic type. Both calculations are discussed and compared withmore » the experimental results. {copyright} {ital 1997} {ital The American Physical Society}« less
118645748
Fusion of radioactive Sn-132 with Ni-64 at sub-barrier energies
Sub-barrier fusion of 132 Sn and 64 Ni was measured at E beam = 465 MeV with an improved apparatus. The result of this new measurement is well reproduced by a coupled-channel calculation and a density-constrained time-dependent Hartree-Fock calculation. The previously measured cross section at E beam = 453 MeV was reanalyzed. Only an upper limit of the cross section was obtained.