General soft terms from Supergravity including D-terms

We derive general expressions for soft terms in supergravity where D-terms contribute significantly to the supersymmetry breaking. Such D-terms can produce large splitting between scalar and fermionic partners in the spectrum. By requiring that supersymmetry breaking sets the cosmological constant to zero, we then parameterize the soft terms when D-terms dominate over F-terms or are comparable to them. We present an application of our results to the split supersymmetry scenario and briefly address the issue of moduli stabilisation.Comment: 6 Pages, no figures. To appear in proceedings of the XXXXth Rencontres de Moriond "Electroweak Interactions and Unified Theories", La Thuile, Italy, March 5-12, 2005; V2 Typos in eq.(9) corrected and other improvement

A little more Gauge Mediation and the light Higgs mass

We consider minimal models of gauge mediated supersymmetry breaking with an extra $U(1)$ factor in addition to the Standard Model gauge group. A $U(1)$ charged, Standard Model singlet is assumed to be present which allows for an additional NMSSM like coupling, $\lambda H_u H_d S$. The U(1) is assumed to be flavour universal. Anomaly cancellation in the MSSM sector requires additional coloured degrees of freedom. The $S$ field can get a large vacuum expectation value along with consistent electroweak symmetry breaking. It is shown that the lightest CP even Higgs boson can attain mass of the order of 125 GeV.Comment: 29 pages, 7 Figures; v2: updated references 30 pages, minor wordings modified, to appear in Nucl. Phys.

Ultrafast generation and decay of a surface metal

Band bending at semiconductor surfaces induced by chemical doping or electric fields can create metallic surfaces with properties not found in the bulk, such as high electron mobility, magnetism or superconductivity. Optical generation of such metallic surfaces via BB on ultrafast timescales would facilitate a drastic manipulation of the conduction, magnetic and optical properties of semiconductors for high-speed electronics. Here, we demonstrate the ultrafast generation of a metal at the (10-10) surface of ZnO upon photoexcitation. Compared to hitherto known ultrafast photoinduced semiconductor-to-metal transitions that occur in the bulk of inorganic semiconductors, the metallization of the ZnO surface is launched by 3-4 orders of magnitude lower photon fluxes. Using time- and angle-resolved photoelectron spectroscopy, we show that the phase transition is caused by photoinduced downward surface band bending due to photodepletion of donor-type deep surface defects. At low photon flux, surface-confined excitons are formed. Above a critical exciton density, a Mott transition occurs, leading to a partially filled metallic band below the equilibrium Fermi energy. This process is in analogy to chemical doping of semiconductor surfaces. The discovered mechanism is not material-specific and presents a general route for controlling metallicity confined to semiconductor interfaces on ultrafast timescales

Bulk Majorana mass terms and Dirac neutrinos in Randall Sundrum Model

We present a novel scheme where Dirac neutrinos are realized even if lepton number violating Majorana mass terms are present. The setup is the Randall-Sundrum framework with bulk right handed neutrinos. Bulk mass terms of both Majorana and Dirac type are considered. It is shown that massless zero mode solutions exist when the bulk Dirac mass term is set to zero. In this limit, it is found that the effective 4D small neutrino mass is primarily of Dirac nature with the Majorana type contributions being negligible. Interestingly, this scenario is very similar to the one known with flat extra dimensions. Neutrino phenomenology is discussed by fitting both charged lepton masses and neutrino masses simultaneously. A single Higgs localised on the IR brane is highly constrained as unnaturally large Yukawa couplings are required to fit charged lepton masses. A simple extension with two Higgs doublets is presented which facilitates a proper fit for the lepton masses.Comment: 13 Pages, Few clarifications included and added references. Figure removed. Published in PR

Clockwork for Neutrino Masses and Lepton Flavor Violation

We investigate the generation of small neutrino masses in a clockwork framework which includes Dirac mass terms as well as Majorana mass terms for the new fermions. We derive analytic formulas for the masses of the new particles and for their Yukawa couplings to the lepton doublets, in the scenario where the clockwork parameters are universal. When the Majorana masses all vanish, the zero mode of the clockwork sector forms a Dirac pair with the active neutrino, with a mass which is in agreement with oscillations experiments for a sufficiently large number of clockwork gears. On the other hand, when the Majorana masses do not vanish, neutrino masses are generated via the seesaw mechanism. In this case, and due to the fact that the effective Yukawa couplings of the higher modes can be sizable, neutrino masses can only be suppressed by postulating a large Majorana mass for all the gears. Finally, we discuss the constraints on the mass scale of the clockwork fermions from the non-observation of the rare leptonic decay $\mu\rightarrow e\gamma$.Comment: 11 pages, 7 figure

Classical running of neutrino masses from six dimensions

We discuss a six dimensional mass generation for the neutrinos. Active neutrinos live on a three-brane and interact via a brane localized mass term with a bulk six-dimensional standard model singlet (sterile) Weyl fermion, the two dimensions being transverse to the three-brane. We derive the physical neutrino mass spectrum and show that the active neutrino mass and Kaluza-Klein masses have a logarithmic cutoff divergence related to the zero-size limit of the three-brane in the transverse space. This translates into a renormalisation group running of the neutrino masses above the Kaluza-Klein compactification scale coming from classical effects, without any new non-singlet particles in the spectrum. For compact radii in the eV--MeV range, relevant for neutrino physics, this scenario predicts running neutrino masses which could affect, in particular, neutrinoless double beta decay experiments.Comment: 23 pages, 2 figure