Soft-Gluon Resummation for Bottom Fragmentation in Top Quark Decay

We study soft-gluon radiation in top quark decay within the framework of perturbative fragmentation functions. We present results for the b-quark energy distribution, accounting for soft-gluon resummation in both the MSbar coefficient function and in the initial condition of the perturbative fragmentation function. The results show remarkable improvement and the b-quark energy spectrum in top quark decay exhibits very little dependence on factorization and renormalization scales. We present some hadron-level results in both x_B and moment space by including non-perturbative information determined from e+e- data.Comment: 19 pages, 6 figures, JHEP style. Few changes after referee report, one reference added, numerical results unchange

Updated Constraints on the Minimal Supergravity Model

Recently, refinements have been made on both the theoretical and experimental determinations of the i.) mass of the lightest Higgs scalar (m_h), ii.) relic density of cold dark matter in the universe (Omega_CDM h^2), iii.) branching fraction for radiative B decay BF(b \to s \gamma), iv.) muon anomalous magnetic moment (a_\mu), and v.) flavor violating decay B_s \to \mu^+\mu^-. Each of these quantities can be predicted in the MSSM, and each depends in a non-trivial way on the spectra of SUSY particles. In this paper, we present updated constraints from each of these quantities on the minimal supergravity (mSUGRA) model as embedded in the computer program ISAJET. The combination of constraints points to certain favored regions of model parameter space where collider and non-accelerator SUSY searches may be more focussed.Comment: 20 pages, 6 figures. Version published 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

Ceramic identity contributes to mechanical properties and osteoblast behavior on macroporous composite scaffolds.

Implants formed of metals, bioceramics, or polymers may provide an alternative to autografts for treating large bone defects. However, limitations to each material motivate the examination of composites to capitalize on the beneficial aspects of individual components and to address the need for conferring bioactive behavior to the polymer matrix. We hypothesized that the inclusion of different bioceramics in a ceramic-polymer composite would alter the physical properties of the implant and the cellular osteogenic response. To test this, composite scaffolds formed from poly(lactide-co-glycolide) (PLG) and either hydroxyapatite (HA), β-tricalcium phosphate (TCP), or bioactive glass (Bioglass 45S®, BG) were fabricated, and the physical properties of each scaffold were examined. We quantified cell proliferation by DNA content, osteogenic response of human osteoblasts (NHOsts) to composite scaffolds by alkaline phosphatase (ALP) activity, and changes in gene expression by qPCR. Compared to BG-PLG scaffolds, HA-PLG and TCP-PLG composite scaffolds possessed greater compressive moduli. NHOsts on BG-PLG substrates exhibited higher ALP activity than those on control, HA-, or TCP-PLG scaffolds after 21 days, and cells on composites exhibited a 3-fold increase in ALP activity between 7 and 21 days versus a minimal increase on control scaffolds. Compared to cells on PLG controls, RUNX2 expression in NHOsts on composite scaffolds was lower at both 7 and 21 days, while expression of genes encoding for bone matrix proteins (COL1A1 and SPARC) was higher on BG-PLG scaffolds at both time points. These data demonstrate the importance of selecting a ceramic when fabricating composites applied for bone healing

"MESSINA 1908-2008” Progetto di ricerca integrato sull'area Calabro – Peloritana: la campagna sismica

Nell’ambito del Progetto Messina 1908- 2008, il Centro Nazionale Terremoti (CNT) in collaborazione con la Sezione di Catania, ha progettato e realizzato un esperimento di sismica passiva con l’obiettivo di raccogliere nuovi dati sismologici nell’area colpita dal terremoto del 1908, uno degli eventi più distruttivi della storia sismica recente italiana

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

Radiative production of invisible charginos in photon photon collision

If in a supersymmetric model, the lightest chargino is nearly degenerate with the lightest neutralino, the former can decay into the latter alongwith a soft pion (or a lepton-neutrino pair). Near degeneracy of the chargino and neutralino masses can cause the other decay products (the pion or the lepton) to be almost invisible. Photon-photon colliders offer a possibility of clean detection of such an event through a hard photon tag.Comment: 12 pages, 5 postscript figure

Spontaneous CP Violation in Non-Minimal Supersymmetric Models

We study the possibilities of spontaneous CP violation in the Next-to-Minimal Supersymmetric Standard Model with an extra singlet tadpole term in the scalar potential. We calculate the Higgs boson masses and couplings with radiative corrections including dominant two loop terms. We show that it is possible to satisfy the LEP constraints on the Higgs boson spectrum with non-trivial spontaneous CP violating phases. We also show that these phases could account for the observed value of epsilonK.Comment: 21 pages, 7 Figures in Encapsulated Postscrip

Probing Lepton Flavor Violation Signal Induced by R-violating Minimal Supersymmetric Standard Model at a Linear Collider

The lepton-flavor violation (LFV) effect at an $e^+e^-$ linear collider (LC), in the frame of R-parity violating minimal supersymmetric standard model is studied. We take the R-parity violating processes $e^+e^-\to e^{\mp}\mu^{\pm}$ as signal, and define the summation of the two processes as ``experiment'' observable. We find that the cross-section summation can reach $\cal{O}$$(10^1)fb$ in the parameter space without sneutrino resonance effect($\sqrt{s} \sim m_{\tilde{\nu}}$). The summation treatment manifests uniform differential distribution on $\cos\theta$, where $\theta$ denotes the polar angles of both outgoing $e^+/e^-$ respectively to incoming electron beam in two signal processes. The uniform feature together with $e\mu$ collinearity would help to reduce the SM background dramatically. Consequently we conclude that at a $500 GeV$ LC with $480 fb^{-1}$ annual luminosity, it's either possible to detect the distinctive R-violating LFV $e\mu$ signal, or exclude sneutrino to $m_{\tilde{\nu}}>1.1 TeV$ at 95% CL in the machine's biennial runtime interval.Comment: 14 pages, 9 figure