1,5-asymmetric induction in the boron-mediated aldol reactions of beta-oxygenated methyl ketones

High levels of substrate-based 1,5-stereoinduction are obtained in the boron-mediated aldol reactions of P-oxygenated methyl ketones with achiral and chiral aldehydes. Remote induction from the boron enolates gives the 1,5-anti adducts, with the enolate pi-facial selectivity critically dependent upon the nature of the beta-alkoxy protecting group. This 1,5-anti aldol methodology has been strategically employed in the total synthesis of several natural products. At present, the origin of the high level of 1,5-anti induction obtained with the boron enolates is unclear, although a model based on a hydrogen bonding between the alkoxy oxygen and the formyl hydrogen has been recently proposed.3082007201

l W nu production at CLIC: a window to TeV scale non-decoupled neutrinos

We discuss single heavy neutrino production e+ e- -> N nu -> l W nu, l = e, mu, tau, at a future high energy collider like CLIC, with a centre of mass energy of 3 TeV. This process could allow to detect heavy neutrinos with masses of 1-2 TeV if their coupling to the electron V_eN is in the range 0.004-0.01. We study the dependence of the limits on the heavy neutrino mass and emphasise the crucial role of lepton flavour in the discovery of a positive signal at CLIC energy. We present strategies to determine heavy neutrino properties once they are discovered, namely their Dirac or Majorana character and the size and chirality of their charged current couplings. Conversely, if no signal is found, the bound V_eN < 0.002-0.006 would be set for masses of 1-2 TeV, improving the present limit up to a factor of 30. We also extend previous work examining in detail the flavour and mass dependence of the corresponding limits at ILC, as well as the determination of heavy neutrino properties if they are discovered at this collider.Comment: LaTeX 32 pages. Added comments and references. Matches version to appear in JHE

Non-universal gauge boson Z′Z' and the spin correlation of top quark pair production at e−e+e^{-}e^{+} colliders

In the off-diagonal basis, we discuss the contributions of the non-universal gauge boson $Z'$ predicted by the topcolor-assisted technicolor ($TC2$) model to the spin configurations and the spin correlation observable of the top quark pair production via the process $e^{-}e^{+}\to t\bar{t}$. Our numerical results show that the production cross sections for the like-spin states, which vanish in the standard model, can be significantly large as $M_{Z'}\approx \sqrt{S}$. With reasonable values of the $Z'$ mass $M_{Z'}$ and the coupling parameter $k_{1}$, $Z'$ exchange can generate large corrections to the spin correlation observable.Comment: 16 pages, 5 figure

Production and FCNC decay of supersymmetric Higgs bosons into heavy quarks in the LHC

We analyze the production and subsequent decay of the neutral MSSM Higgs bosons (h = h^0, H^0, A^0) mediated by flavor changing neutral currents (FCNC) in the LHC collider. We have computed the h-production cross-section times the FCNC branching ratio, \sigma(pp -> h -> qq') = \sigma(pp -> h) B(h -> qq'), in the LHC focusing on the strongly-interacting FCNC sector. Here qq' is an electrically neutral pair of quarks of different flavors, the dominant modes being those containing a heavy quark: tc or bs. We determine the maximum production rates for each of these modes and identify the relevant regions of the MSSM parameter space, after taking into account the severe restrictions imposed by low energy FCNC processes. The analysis of \sigma(pp -> h -> qq') singles out regions of the MSSM parameter space different from those obtained by maximizing only the branching ratio, due to non-trivial correlations between the parameters that maximize/minimize each isolated factor. The production rates for the bs channel can be huge for a FCNC process (0.1-1 pb), but its detection can be problematic. The production rates for the tc channel are more modest (10^{-3}-10^{-2} pb), but its detection should be easier due to the clear-cut top quark signature. A few thousand tc events could be collected in the highest luminosity phase of the LHC, with no counterpart in the SM.Comment: 25 pages, 9 figures, 2 tables, LaTeX 2e. Typos corrected. Version to appear in JHE

Constraining Dark Matter in the MSSM at the LHC

In the event that R-Parity conserving supersymmetry (SUSY) is discovered at the LHC, a key issue which will need to be addressed will be the consistency of that signal with astrophysical and non-accelerator constraints on SUSY Dark Matter. This issue is studied for the SPA benchmark model based on measurements of end-points and thresholds in the invariant mass spectra of various combinations of leptons and jets. These measurements are used to constrain the soft SUSY breaking parameters at the electroweak scale in a general MSSM model. Based on these constraints, we assess the accuracy with which the Dark Matter relic density can be measured.Comment: 21 pages, 12 figure

Unparticle physics in top pair signals at the LHC and ILC

We study the effects of unparticle physics in the pair productions of top quarks at the LHC and ILC. By considering vector, tensor and scalar unparticle operators, as appropriate, we compute the total cross sections for pair production processes depending on scale dimension d_{\U}. We find that the existence of unparticles would lead to measurable enhancements on the SM predictions at the LHC. In the case of ILC this may become two orders of magnitude larger than that of SM, for smaller values of d_\U, a very striking signal for unparticles.Comment: 19 pages, 9 figures, analysis for ILC has been adde

Unparticle Physics in Single Top Signals

We study the single production of top quarks in $e^+e^-, ep$ and $pp$ collisions in the context of unparticle physics through the Flavor Violating (FV) unparticle vertices and compute the total cross sections for single top production as functions of scale dimension d_{\U}. We find that among all, LHC is the most promising facility to probe the unparticle physics via single top quark production processes.Comment: 14 pages, 10 figure

Flavor Changing Neutral Currents involving Heavy Quarks with Four Generations

We study various FCNC involving heavy quarks in the Standard Model (SM) with a sequential fourth generation. After imposing $B\to X_s\gamma$, $B\to X_sl^+l^-$ and $Z\to b\bar{b}$ constraints, we find ${\cal B}(Z\to s\bar{b}+\bar{s}b)$ can be enhanced by an order of magnitude to $10^{-7}$, while $t\to cZ, cH$ decays can reach $10^{-6}$, which are orders of magnitude higher than in SM. However,these rates are still not observable for the near future.With the era of LHC approaching, we focus on FCNC decays involving fourth generation $b^\prime$ and $t^\prime$ quarks. We calculate the rates for loop induced FCNC decays $b^\prime\to bZ, bH, bg, b\gamma$, as well as t^\prime\to tZ,\tH, tg, t\gamma. If $|V_{cb'}|$ is of order $|V_{cb}| \simeq 0.04$, tree level $b^\prime\to cW$ decay would dominate, posing a challenge since $b$-tagging is less effective. For $|V_{cb'}| \ll |V_{cb}|$, $b'\to tW$ would tend to dominate, while $b'\to t^\prime W^*$ could also open for heavier $b'$, leading to thepossibility of quadruple-$W$ signals via $b'\bar b'\to b\bar b W^+W^-W^+W^-$. The FCNC $b'\to bZ, bH$ decays could still dominate if $m_{b'}$ is just above 200 GeV. For the case of $t'$, ingeneral $t^\prime\to bW$ would be dominant, hence it behaves like a heavy top. For both $b'$ and $t'$, except for the intriguing light $b'$ case, FCNC decays are in the $10^{-4} -10^{-2}$ range, and are quite detectable at the LHC.For a possible future ILC, we find the associated production of FCNC $e^+e^-\to b\bar s$, $t\bar c$ are below sensitivity, while $e^+e^-\to b^\prime\bar b$ and$t^\prime\bar t$ can be better probed.Tevatron Run-II can still probe the lighter $b'$ or $t'$ scenario. LHC would either discover the fourth generation and measure the FCNC rates, or rule out the fourth generation conclusively.Comment: 31 pages, 15 eps figures, version to appear in JHE

A T-odd asymmetry in neutralino production and decay

We study CP-violating effects in neutralino production and subsequent decay within the Minimal Supersymmetric Standard Model with complex parameters M_1 and mu. The observable we propose is a T-odd asymmetry based on a triple product in neutralino production e^+ e^- -> tilde{chi}^0_i tilde{chi}^0_2, i = 1,...,4, with subsequent leptonic three-body decay tilde{chi}^0_2 -> tilde{chi}^0_1 l^+ l^-, l = e, mu, at an e^+ e^- linear collider with sqrt{s} = 500 GeV and polarised beams. We provide compact analytical formulae for the cross section and the T-odd asymmetry taking into account the complete spin correlations between production and decay. We give numerical predictions for the cross section and the T-odd asymmetry. The asymmetry can go up to 10 %.Comment: 28 pages, LaTeX, 10 figures; v2: typos corrected, published versio

Growth of Synechococcus sp. immobilized in chitosan with different times of contact with NaOH

The thickness of the walls of the capsules of chitosan-immobilized Synechococcus cultures was dependent on the time of contact with NaOH and was directly related to culture growth. After an initial lag phase, probably caused by cell damage, the capsules obtained after 80 s in a 0.1 N NaOH solution showed better growth than that of free cell cultures (6.9 and 5.2 divisions in 10 days, respectively)