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Search Results: 1 - 10 of 235806 matches for " James D. Thomas "
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Massive Doublet Leptons
Scott Thomas,James D. Wells
Physics , 1998, DOI: 10.1103/PhysRevLett.81.34
Abstract: Massive vector-like electroweak doublets are generic in many extensions of the standard model. Even though one member of the doublet is necessarily electrically charged these particles are not easily detected in collider experiments. The neutral and charged states within the doublet are split by electroweak symmetry breaking. In the absence of mixing with other states, the radiatively generated splitting is in the range 200 - 350 MeV for m > mZ/2. The charged state decays to the neutral one with an O(cm) decay length, predominantly by emission of a soft charged pion. The best possibility to detect these massive charged particles is to trigger on hard initial state radiation and search for two associated soft charged pions with displaced vertices. The mass reach for this process at LEPII is limited by luminosity rather than kinematics.
EGR1 is essential for transcriptional regulation of BMPR2  [PDF]
Radhika Gaddipati, James D. West, James E. Loyd, Thomas Blackwell, Kirsten A. Lane, Nicole M. Lane, Kirk B. Lane
American Journal of Molecular Biology (AJMB) , 2011, DOI: 10.4236/ajmb.2011.13014
Abstract: In this study, RLM-RACE was used to identify the transcriptional start site 387 bp upstream of the translational start. Evolutionarily conserved transcription factor binding sites were identified, and a series of luciferase reporter constructs driven by BMPR2 promoter elements used to determine their functional relevance. We found the promoter area from 983 bp to 90 bp upstream of the transcriptional start gave maximal activity, greater than longer constructs, with an area between 570 bp and 290 bp upstream of the transcriptional start containing an important repressor element. To characterize this repressor, we used a combination of EMSA, mutation of the EGR1 binding site, transfection with EGR1 and NAB1 constructs, and mutation of the NAB1 binding site within the EGR1 protein. From this we conclude that EGR1 is essential to BMPR2 transcription, but that NAB1 binding to EGR1 causes it to act as a repressor.
Distinguishing the parasitic wasp, Peristenus howardi, from some of its congeners using polymerase chain reaction and restriction endonuclease digestion
Thomas M. Mowry,James D. Barbour
Journal of Insect Science , 2004,
Abstract: A molecular procedure incorporating polymerase chain reaction (PCR) of the COI gene and restriction endonuclease digestion of PCR products was used to distinguish Peristenus howardi (Hymenoptera: Braconidae) from four other Peristenus species. Non-solvent extraction of parasite DNA using a commercially available kit proved to be very effective in producing amplifiable template. Use of SfcI endonuclease produced restriction fragments with banding patterns in agarose gel electrophoresis that readily separated P. howardi, P. digoneutis, P. conradi, P. pallipes, and P. pseudopallipes.. However, while the restriction fragment banding patterns of both P. pallipes and P. pseudopallipes were easily distinguishable from the other Peristenus species, they could not be reliably separated from one another. This molecular procedure can be used in applied and ecological research to better understand the role of P. howardi in the Peristenus-Lygus parasite-host system within the Pacific Northwest. Consensus sequences of our amplimers for all five Peristenus spp. are deposited in GenBank under accession numbers AY626370, AY626371, AY626372, AY626373, and AY626374.
Testing Low Energy Theorems in Nucleon-Nucleon Scattering
Thomas D. Cohen,James M. Hansen
Physics , 1999, DOI: 10.1103/PhysRevC.59.3047
Abstract: Low energy theorems have been derived for the coefficients of the effective range expansion in s-wave nucleon-nucleon scattering valid to leading nontrivial order in an expansion based $Q$ counting, a scheme in which both $m_\pi$ and $1/a$ (where $a$ is the scattering length) are treated as small mass scales. Previous tests of these theorems based on coefficients extracted from scattering data indicate a pattern of gross violations which suggested serious problems for the perturbative treatment of pions implicit in $Q$ counting. We discuss the possibility that uncertainties associated with extracting the coefficients from the scattering data make such tests invalid. Here we show that errors in the s-wave phase shift extractions are sufficiently small to test direct test predictions from $Q$ counting at next to leading order. In particular we show that there exist low energy theorems for the sum of all terms in the effective range expansion beyond the first two which allow for precise tests. These low energy theorems fail badly which suggests that pionic aspects of $Q$ counting are not under control.
Sparticle Spectroscopy and Electroweak Symmetry Breaking with Gauge-Mediated Supersymmetry Breaking
Savas Dimopoulos,Scott Thomas,James D. Wells
Physics , 1996, DOI: 10.1016/S0550-3213(97)00030-8
Abstract: The phenomenology associated with gauge-mediated supersymmetry breaking is presented. A renormalization group analysis of the minimal model is performed in which the constraints of radiative electroweak symmetry breaking are imposed. The resulting superpartner and Higgs boson spectra are highly correlated and depend on only a few parameters. Superpartner mass ratios and sum rules are identified which can be tested at future colliders. Some of these relations are logarithmically sensitive to the messenger scale, while others allow gauge-mediation to be distinguished from other schemes for tansmitting supersymmetry breaking. Deviations from the minimal model, such as larger messenger representations and additional contributions to Higgs sector masses, can in some circumstances dramatically modify the low energy spectrum. These modifications include a slepton or Higgsino as the lightest standard model superpartner, or exotic mass relations among the scalars and gauginos. The contribution to $b \to s \gamma$ and resulting bound on superpartner masses are also presented for the minimal model. Finally, the unique collider signatures of heavy charged particle production, or decay to the Goldstino within a detector are discussed.
Implications of Low Energy Supersymmetry Breaking at the Tevatron
Savas Dimopoulos,Scott Thomas,James D. Wells
Physics , 1996, DOI: 10.1103/PhysRevD.54.3283
Abstract: The signatures for low energy supersymmetry breaking at the Tevatron are investigated. It is natural that the lightest standard model superpartner is an electroweak neutralino, which decays to an essentially massless Goldstino and photon, possibly within the detector. In the simplest models of gauge-mediated supersymmetry breaking, the production of right-handed sleptons, neutralinos, and charginos leads to a pair of hard photons accompanied by leptons and/or jets with missing transverse energy. The relatively hard leptons and softer photons of the single $e^+e^- \gamma \gamma + \EmissT$ event observed by CDF implies this event is best interpreted as arising from left-handed slepton pair production. In this case the rates for $l^{\pm} \gamma \gamma + \EmissT$ and $ \gamma \gamma + \EmissT$ are comparable to that for $l^+l^- \gamma \gamma + \EmissT$.
Systematic Power Counting in Cutoff Effective Field Theories for Nucleon-Nucleon Interactions and the Equivalence With PDS
Thomas D. Cohen,James M. Hansen
Physics , 1998, DOI: 10.1016/S0370-2693(98)01180-0
Abstract: An analytic expression for the ${}^1S_0$ phase shifts in nucleon-nucleon scattering is derived in the context of the Schr\"odinger equation in configuration space with a short distance cutoff and with a consistent power counting scheme including pionic effects. The scheme treats the pion mass and the inverse scattering length over the intrinsic short distance scale as small parameters. Working at next-to-leading order in this scheme, we show that the expression obtained is identical to one obtained using the recently introduced PDS approach which is based on dimensional regularization with a novel subtraction scheme. This strongly supports the conjecture that the schemes are equivalent provided one works to the same order in the power counting.
Low Energy Theorems For Nucleon-Nucleon Scattering
Thomas D. Cohen,James M. Hansen
Physics , 1998, DOI: 10.1103/PhysRevC.59.13
Abstract: Low energy theorems are derived for the coefficients of the effective range expansion in s-wave nucleon-nucleon scattering valid to leading order in an expansion in which both $m_\pi$ and $1/a$ (where $a$ is the scattering length) are treated as small mass scales. Comparisons with phase shift data, however, reveal a pattern of gross violations of the theorems for all coefficients in both the $^1S_0$ and $^3S_1$ channels. Analogous theorems are developed for the energy dependence $\epsilon$ parameter which describes $^3S_1 - ^3D_1$ mixing. These theorems are also violated. These failures strongly suggest that the physical value of $m_\pi$ is too large for the chiral expansion to be valid in this context. Comparisons of $m_\pi$ with phenomenological scales known to arise in the two-nucleon problem support this conjecture.
Electroweak precision measurements and collider probes of the Standard Model with large extra dimensions
Thomas G. Rizzo,James D. Wells
Physics , 1999, DOI: 10.1103/PhysRevD.61.016007
Abstract: The elementary particles of the Standard Model may live in more than 3+1 dimensions. We study the consequences of large compactified dimensions on scattering and decay observables at high-energy colliders. Our analysis includes global fits to electroweak precision data, indirect tests at high-energy electron-positron colliders (LEP2 and NLC), and direct probes of the Kaluza-Klein resonances at hadron colliders (Tevatron and LHC). The present limits depend sensitively on the Higgs sector, both the mass of the Higgs boson and how many dimensions it feels. If the Higgs boson is trapped on a 3+1 dimensional wall with the fermions, large Higgs masses (up to 500 GeV) and relatively light Kaluza-Klein mass scales (less than 4 TeV) can provide a good fit to precision data. That is, a light Higgs boson is not necessary to fit the electroweak precision data, as it is in the Standard Model. If the Higgs boson propagates in higher dimensions, precision data prefer a light Higgs boson (less than 260 GeV), and a higher compactification scale (greater than 3.8 TeV). Future colliders can probe much larger scales. For example, a 1.5 TeV electron-positron linear collider can indirectly discover Kaluza-Klein excitations up to 31 TeV if 500 fb^-1 integrated luminosity is obtained.
The Predictive Power of Effective Field Theory in NN Scattering: ^3S_1-^3D_1 Mixing at Next-to Next-to Leading Order
Thomas D. Cohen,James M. Hansen
Physics , 1999,
Abstract: The convergence of the Q expansion in the ^3S_1-^3D_1 mixing angle is investigated through the renormalization condition used to fit the free paramteter encountered at NNLO. Although the NNLO calculation describes the data well at momenta much less than 50 MeV, a variation in the renormalization condition results in 100% expected uncertainties at momenta as low as 100 MeV. This uncertainty can be traced to the presence of large cancelations between terms entering at NNLO, which are found to be several times larger than the terms entering at NLO. This implies a fundamental lack of predictive power at this order int he Q expansion of \epsilon_1. Given the small empirical size, this lack of predictive power is easily understood in terms of simple power counting arguments.
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