Low Tan Research Articles

M-type Hexaferrite for Gigahertz Chip Antenna Applications

We demonstrate that Sn/Zn-substituted strontium M-type hexaferrite (SrSn2.5Zn2.5Fe7O19 = Sn/Zn-SrM) can provide high performance and a uniform radiation pattern over a wide frequency band for gigahertz chip-antenna applications. Saturation magnetization and coercivity were 68.5 emu/g and 46 Oe. Real parts of permeability and permittivity were 1.37 (loss tan δμ = 0.13) and 22.2 (loss tan δe = 0.09) at 2.44 GHz, respectively. A Bluetooth Sn/Zn-SrM chip antenna has a bandwidth of 780 MHz (2.15-2.93 GHz) at S11 <; -10 dB, maximum three-dimensional (3-D) peak gain of 1.25 dBi, and radiation efficiency of 60% at 2.4 GHz. Our antenna performance simulation suggests that radiation efficiency can be increased up to 98% with a low magnetic loss tan δμ of 0.01. 3-D radiation patterns were omnidirectional in the Bluetooth frequency range. Therefore, Sn/Zn-substituted strontium M-type hexaferrite is a promising magnetic material for future gigahertz antenna applications.

Implications of large dimuon CP asymmetry in B d,s decays on minimal flavor violation with low tan β

The D0 collaboration has recently announced evidence for a dimuon CP asymmetry in B_{d,s} decays of order one percent. If confirmed, this asymmetry requires new physics. We argue that for minimally flavor violating (MFV) new physics, and at low tan beta=v_u/v_d, there are only two four-quark operators (Q_{2,3}) that can provide the required CP violating effect. The scale of such new physics must lie below 260 GeV sqrt{tan beta}. The effect is universal in the B_s and B_d systems, leading to S_{psi K}~sin(2beta)-0.15 and S_{psi phi}~0.25. The effects on epsilon_K and on electric dipole moments are negligible. The most plausible mechanism is tree-level scalar exchange. MFV supersymmetry with low tan beta will be excluded. Finally, we explain how a pattern of deviations from the Standard Model predictions for S_{psi phi}, S_{psi K} and epsilon_K can be used to test MFV and, if MFV holds, to probe its structure in detail.

Characterization of Ageing for MV Power Cables Using Low Frequency Tan δ Diagnostic Measurements

This paper describes very low frequency (VLF) tan delta experiments performed on field-aged and non-aged distribution medium voltage (MV) cable samples. The field aged samples constitute a uniform set of Cross-linked Polyethylene (XLPE) of 15 kV unjacketed cables removed from the same service area having experienced similar operating and ageing conditions. The non-aged samples are a diverse set of crosslinked polyethylene (XLPE) and water tree retardant cross-linked polyethylene (WTRXLPE) cables of 15 kV and 25 kV and Ethylene Propylene Rubber (EPR) cable of 25 kV. The experiments are designed to contribute in understanding, time, voltage and discharge time dependence of Tan delta diagnostic measurements at VLF of 0.1 Hz. Results help in clarifying issues that arise when characterizing MV cable insulation by Tan delta diagnostic measurements. The issues include time-on-test, voltage level as a diagnostic tool, diagnostic features, and reproducibility and repeatability of the measurements. The paper shows that higher insulation losses, non-linearity, hyteresis, and variation in voltage and time of Tan delta diagnostic measurements at VLF are indicators that can be used to properly characterize the insulation and enhance the diagnosis.

The MFV limit of the MSSM for low tan β: meson mixings revisited

We apply the effective field theory definition of Minimal Flavour Violation (MFV) to the MSSM. We explicitly show how, by this definition, the new sources of flavour and CP violation present in the MSSM become functions of the SM Yukawa couplings, and cannot be simply set to zero, as is common wisdom in phenomenological MSSM studies that assume MFV. We apply our approach to the MSSM Delta B = 2 Hamiltonian at low tan(beta). The limit of MFV amounts to a striking increase in the predictivity of the model. In particular, SUSY corrections to meson-antimeson mass differences Delta M(d,s) are always found to be positive with respect to the SM prediction. This feature is due to an interesting interplay between chargino and gluino box diagrams (the dominant contributions) in the different mass regimes one can consider. Finally, we point out that, due to the presence of gluinos, the MFV MSSM does not belong -- even at low tan(beta) -- to the class of models with the so-called `constrained' MFV (CMFV), in which only the SM operator (V-A)x(V-A) contributes to Delta M(d,s). Consequently, for the MSSM and in the general case of MFV, one should not use the Universal Unitarity Triangle (UUT), relevant for CMFV models, but a MFV-UT constructed from beta(psi KS) and |V(ub)| or gamma from tree level decays. In particular, with the measured value of beta(psi KS), MFV implies a testable correlation between |V(ub)| and gamma. With the present high value of |V(ub)|, MFV favours gamma > 80 degrees.

Lower bounds on ΔMs,dfrom constrained minimal flavour violation

We demonstrate that in the class of models with Constrained Minimal Flavour Violation (CMFV), in which the CKM matrix is the only source of CP violation and B^0_q-\bar B^0_q mixings (q=d,s) are described by a single operator (\bar b q)_{V-A} (\bar b q)_{V-A}, the lower bounds on the mass differences Delta M_{s,d} are simply given by their Standard Model values (Delta M_{s,d})_SM with two possible exceptions that we identify. Our proof involves all possible charged gauge boson, Goldstone boson and physical charged and neutral scalar exchanges and assumes that the masses of new charge +2/3 singlet heavy fermions T_i that mix with the top quark have all to be larger than m_t, which is chosen by nature. Similarly, the additional charged gauge bosons have to satisfy M_i>M_W, while no such bound needs to be set on the charged and neutral scalar masses. The two possible exceptions arise in the presence of U(1) neutral gauge bosons and Majorana fermions in box diagrams with flavour violating couplings. However in the case of the MSSM with CMFV and low tan beta our bound is satisfied in spite of gluino and neutralino contributions.

Minimal flavour violation waiting for precise measurements of ΔMs,Sψphi,AsSL, |Vub|, γ andB0s,d→μ+μ−

We emphasize that the recent measurements of the B^0_s - bar B^0_s mass difference Delta M_s by the CDF and D0 collaborations offer an important model independent test of minimal flavour violation (MFV). The improved measurements of the angle gamma in the unitarity triangle and of |V_ub| from tree level decays, combined with future accurate measurements of Delta M_s, S_{psi K_S}, S_{psi phi}, Br(B_{d,s} -> mu+ mu-), Br(B -> X_{d,s} nu bar nu), Br(K+ -> pi+ nu bar nu) and Br(K_L -> pi^0 nu bar nu) and improved values of the relevant non-perturbative parameters, will allow to test the MFV hypothesis in a model independent manner to a high accuracy. In particular, the difference between the reference unitarity triangle obtained from tree level processes and the universal unitarity triangle (UUT) in MFV models would signal either new flavour violating interactions and/or new local operators that are suppressed in MFV models with low tan(beta), with the former best tested through S_{psi phi} and K_L -> pi^0 nu bar nu. A brief discussion of non-MFV scenarios is also given. In this context we identify in the recent literature a relative sign error between Standard Model and new physics contributions to S_{psi phi}, that has an impact on the correlation between S_{psi phi} and A^s_SL. We point out that the ratios S_{psi phi}/A^s_SL and (Delta M_s)/(Delta Gamma_s) will allow to determine (Delta M_s)/(Delta M_s)^SM. Similar proposals for the determination of (Delta M_d)/(Delta M_d)^SM are also given.

Atomic Layer Deposition of NbN and Nb(Si)N for Metal Electrodes

Niobium nitride NbN and niobium silicon nitride Nb(Si)N were deposited by Atomic Layer Deposition (ALD) from niobium pentachloride NbCl5, silicon tetrachloride SiCl4, and ammonia NH3. It was shown that low resistivity NbN can be more readily processed by ALD than low resistivity TaN using just NH3 as reducing agent. Silicon could be uniformly added into the NbN structure, and increase in silicon content increased the resistivity of the films due to silicon incorporation as silicon nitride. A successful scale-up onto 200 mm wafer was performed for both processes.

Development of a single-sludge denitrification method for nitrate removal from RAS effluents: Lab-scale results vs. model prediction

A lab-scale activated-sludge type reactor was used to induce denitrification by using the organic solid waste of a typical Recirculating Aquaculture System (RAS) as the electron donor (‘Single-sludge denitrification’). The results were compared with the predictions of a stoichiometry-based model. As predicted by the model, reactor's performance was found to be strongly related to the mean solids retention time (SRT) employed. Measured denitrification rates conformed very well to model predictions. High nitrate removal rates of up to 590 mg N (L reactord) − 1 were recorded at a relatively low SRT of 4 d. Oxygen, that entered the reactor via both atmospheric diffusion and with the stream used to simulate the influent from a fish tank, reduced the amount of organic matter available for denitrification, resulting in lower denitrification rates. This interference was more significant when the system was operated at the longer SRTs. Most of the excess ammonia released to the aqueous phase through ammonification was oxidized (presumably by anammox bacteria) under the prevailing anoxic conditions, resulting in very low effluent TAN concentrations. Phosphate release to the aqueous phase was significantly lower than predicted, suggesting above-typical microbial P assimilation. Reaction kinetics was found to be zero order with respect to nitrate at concentrations of above 1.5 to 2.0 mg N L − 1 . Taken together the findings indicate that intensive single-sludge denitrification for treating RAS effluents is technically feasible, and that the process appears to be a cost-effective solution to reducing both the nutrient and the organic loads generated by intensive fish farms. The main advantages of the method include minimal formation of undesired by-products, small reactor volume and simple control and operation. Furthermore, the process is well described by a conceptual mathematical model, allowing its application as a part of any RAS design.

The tetrasporophyte of Asparagopsis armata as a novel seaweed biofilter

The red seaweed Asparagopsis armata (Harvey; Rhodophytae, Bonnemaisoniaceae) produces biologically active secondary metabolites that are valuable natural ingredients for cosmetics and medicine and its cultivation may therefore be a profitable venture. The tetrasporophyte of this species (“ Falkenbergia rufolanosa”) was successfully tank-cultivated as a continuous biofilter for the effluent of a commercial fish farm in southern Portugal. Optimal stocking density for highest biomass yield and a low level of other algal species in winter and late spring was 5× g centrifuged fresh weight l − 1 . The effect of total ammonia nitrogen supply (TAN flux) on biofiltration and biomass yield was investigated in winter and spring. Results revealed that A. armata is currently the seaweed-biofilter with the highest TAN removal of up to 90 μmol l − 1 h − 1 at a TAN flux of about 500 μmol l − 1 h − 1 . In the tanks used, this is equivalent to a removal of up to 14.5 g TAN m − 2 day − 1 . At a lower TAN flux of about 40 μmol l − 1 h − 1 , TAN removal by A. armata is more than double to what is reported at this flux for another successful seaweed biofilter, the genus Ulva. Monthly variation of A. armata biomass yield peaked in May and was lowest in January. At TAN fluxes between 300 and 400 μmol l − 1 h − 1 , an average water temperature of 21.7 °C and a total daily photon flux density of 47 Mol m − 2 , seaweed yield was over 100 g DW m − 2 day − 1 with a recorded maximum of 119 g. During spring, autumn and early summer, the biomass of A. armata within the experimental tanks doubled every week. A model for the up scaling of this finfish integrated aquaculture of A. armata varies the investment in biofilter surface area and estimates the return in biofiltration and biomass yield. Highest TAN removal efficiencies will only be possible at low TAN fluxes and a very large biofilter area, resulting in a low production of biomass per unit area. To remove 50% of TAN from the effluent (1 mt Sparus aurata; 21 °C), 28 m 2 of biofilter, designed to support a water turnover rate of 0.8 Vol h − 1 would be necessary. This system produces 6.1 kg FW (1.5 kg DW) of A. armata per day and has the potential to turn biofiltration into an economically sustained, beneficial side effect.

Renormalization group invariants in the MSSM and its extensions

We derive one-loop renormalization group (RG) invariant observables and analyze their phenomenological implications in the MSSM and its \mu problem solving extensions, U(1)' model and NMSSM. We show that there exist several RG invariants in the gauge, Yukawa and soft-breaking sectors of each model. In general, RG invariants are highly useful for projecting experimental data to messenger scale, for revealing correlations among the model parameters, and for probing the mechanism that breaks supersymmetry. The Yukawa couplings and trilinear soft terms in U(1)' model and NMSSM do not form RG invariants though there exist approximate invariants in low tan(beta). In the NMSSM, there are no invariants that contain the Higgs mass-squareds. We provide a comparative analysis of RG invariants in all three models and analyze their model-building and phenomenological implications by a number of case studies.

Fabrication of a low resistivity tantalum nitride thin film

Novel bilayer TaN film has been developed using reactive ion DC sputtering. The film has a low resistivity of ∼80 μΩ-cm and is more stable compared with high resistivity films with high nitrogen flow rates. Low angle X-ray diffraction results show that the low resistivity TaN film is highly crystallized than that of each individual film deposited in the bilayer design. The crystalline structure and the film resistivity of the bilayer TaN film remain unchanged even when the thickness of each layer is changed, indicating large process window, that is critical for high volume manufacturing.

Phenomenology of a Fluxed MSSM

We analyze the phenomenology of a set of minimal supersymmetric standard model (MSSM) soft terms inspired by flux-induced supersymmetry (SUSY)-breaking in Type IIB string orientifolds. The scheme is extremely constrained with essentially only two free mass parameters: a parameter M, which sets the scale of soft terms, and the mu parameter. After imposing consistent radiative electro-weak symmetry breaking (EWSB) the model depends upon one mass parameter (say, M). In spite of being so constrained one finds consistency with EWSB conditions. We demonstrate that those conditions have two solutions for mu<0, and none for mu>0. The parameter tan beta results as a prediction and is approximately 3-5 for one solution, and 25-40 for the other, depending upon M and the top mass. We examine further constraints on the model coming from b->s gamma, the muon g-2, Higgs mass limits and WMAP constraints on dark matter. The MSSM spectrum is predicted in terms of the single free parameter M. The low tan beta branch is consistent with a relatively light spectrum although it is compatible with standard cosmology only if the lightest neutralino is unstable. The high tan beta branch is compatible with all phenomenological constraints, but has quite a heavy spectrum. We argue that the fine-tuning associated to this heavy spectrum would be substantially ameliorated if an additional relationship mu=-2M were present in the underlying theory.

Measurement oftanβin associatedtH±production inγγcollisions

The ratio of neutral Higgs field vacuum expectation values, tan beta, is one of the most important parameters to determine in type-II Two-Higgs Doublet Models (2HDM), specifically the Minimal Supersymmetric Standard Model (MSSM). Assuming the energies and integrated luminosity of a future high energy e^+e^- linear collider of sqrt{s}=500, 800, 1000, and 1500 GeV and L=1 ab^{-1} we show that associated t H^+/- production in gamma gamma collisions can be used to make an accurate determination of tan beta for low and high tan beta by precision measurements of the gamma gamma -> H^+/- t + X cross section.

Four body decay of the top squark at the upgraded Fermilab Tevatron

We investigate the prospect of stop squark search at Tevatron RUN-II in mSUGRA motivated as well as unconstrained supersymmetric models, when the lighter stop squark turns out to be the next lightest supersymmetric particle (NLSP). In this case the decay into a 4-body final state consisting of a b quark, the lightest neutralino and two light fermions may compete with the much publicized loop induced two body decay into a charm quark and the lightest neutralino. We systematically study the parameter space in mSUGRA where the lighter stop squark turns out to be the NLSP and calculate the branching ratios of the competing channels in both models. Our results show that the four body decay may indeed be the main discovery channel particularly in the low tan $\beta$ scenarios. We discuss the detectability of stop squark pairs in the 4-body decay channel leading to one lepton with 2 or more jets accompanied by a large amount of missing energy. We also studied the corresponding background processes and the kinematic cuts required to suppress them using parton level Monte Carlo simulations. We have commented upon with illustrative examples, the required revision of the existing mass limits of the stop NLSP assumed to decay solely into the loop induced 2-body channel in the presence of the competing 4-body decay.

Vacuum stability bounds in anomaly and gaugino mediated supersymmetry breaking models

We constrain the parameter space of the minimal and gaugino-assisted anomaly mediation, and gaugino mediation models by requiring that the electroweak vacuum corresponds to the deepest minimum of the scalar potential. In the framework of anomaly mediation models we find strong lower bounds on slepton and squark masses. In the gaugino mediation models the mass spectrum is forced to be at the TeV scale. We find extensive regions of the parameter space which are ruled out, even at low tan(beta). The implications of these results on the g-2 of the muon are also analyzed.

Low-loss behavior of α-PVDF

The exact nature of the polarization processes in low-loss materials is not sufficiently understood and good experimental material is relatively scarce. Dielectric response of /spl alpha/-PVDF covering 8.5 decades of frequency between 10/sup -/2 and 3/spl times/10/sup 6/ Hz and a range of temperatures between 103 and 138 K were analyzed to reveal the nature of the dominant polarization process. Correcting for a series resistance and a Debye-like loss process at 50 kHz, the 'universal' fractional power law of dielectric response is well maintained, the residual tan /spl delta/ falls between 0.002 and 0.02 depending on temperature and frequency, with the residual loss process presumed to be due to hopping charge carriers having an activation energy of 0.035 eV. The universal process itself has a relatively high loss but its amplitude is low and this accounts for the low tan /spl delta/.

Possibility of Nd/sub 1.9/Ba/sub 1.1/Cu/sub 3/O/sub 7+δ/ and Pr/sub 1.14/Ba/sub 1.86/Cu/sub 3/O/sub 7-δ/ single crystals for insulator in high-speed superconducting circuits

Dielectric properties of both Nd/sub 1.9/Ba/sub 1.1/Cu/sub 3/O/sub 7+/spl delta// (NBCO-213) and Pr/sub 1.14/Ba/sub 1.86/Cu/sub 3/O/sub 7-/spl delta// (Pr-rich PBCO) single crystals have been examined at low temperature. These materials have good lattice matching to high-T/sub c/ superconductors (HTS), but they are conductive at room temperature. Below 80 K, they are insulators with low dielectric constants, /spl epsi//sub /spl tau// below 25, and low dielectric loss tan /spl delta/ below 0.1 at 100 kHz. The value of /spl epsi//sub /spl tau// is suitable for insulators in integrated circuits using strip line widths of 10 /spl mu/m order, providing short delay time, no excitation of surface wave, and low radiation loss. The value of tan /spl delta/ is comparable to loss of superconducting surface resistance above 100 GHz. These results indicate the applicability for the insulator layers in multilayer superconducting electronic devices such as Single Flux Quantum (SFQ) circuits operated at high speed.

Process

The one-loop branching ratios for the process Z->h(A)+gamma are calculated in the general Two Higgs Doublet Model (Model II) taking into account existing constraints on the model parameters. For Higgs boson masses below 50 GeV and tan beta of order 1-10 the fraction of such Z decays are at the level of 10^{-7}, but can be significantly stronger for very low or high tan beta, where the dependence of these results on other model parameters like sin(beta-alpha) and the mass of the charged Higgs boson is found to be of little importance. The results are compared to the LEP measurements, which are sensitive to branching ratios of Z->h(A)+gamma of the order 10^{-5} for masses larger than 20 GeV, but approach 10^{-6} for low masses. Relating the expectation to the experimental limits, constraints on the parameter space of the 2HDM are derived.

The MSSM at the low tanβ fixed point is meta-stable

We analyse the mass spectrum of the Constrained Minimal Supersymmetric Standard Model at the low tan beta fixed point. We find that the model only satisfies experimental and dark matter bounds in regions where the vacuum is meta-stable -- ie where it violates `unbounded from below' (UFB) bounds. Adding a small amount of R-parity violation solves these problems but the absolute upper bound on the lowest higgs mass m_{h^0}<97 GeV remains. We present the predicted sparticle mass spectrum as a function of the gluino mass m_g.

Enhanced Three-Body Decay of the Charged Higgs Boson

If the charged Higgs boson H+ exists with mh < mt + mb, the conventional expectation is that it will decay dominantly into c s-bar and tau+ nu-tau. However, the three-body decay mode H+ --> W+ b b-bar is also present and we show that it becomes very important in the low tan(beta) region for mh >~ 140 GeV. We explore its phenomenological implications for the charged-Higgs-boson search in top-quark decay.