arXiv subjects

I. B. Whittingham

Publications and source records attributed to I. B. Whittingham.

13 recordsLinked to original sources

arXiv2019

Ultracold homonuclear and heteronuclear collisions in metastable helium

Scattering and ionizing cross sections and rates are calculated for ultracold collisions between metastable helium atoms using a fully quantum-mechanical close-coupled formalism. Homonuclear collisions of the bosonic ${}^{4}$He$^{*} +{}^{4}$He$^{*}$ and fermionic ${}^{3}$He$^{*} + {}^{3}$He$^{*}$ systems, and heteronuclear collisions of the mixed ${}^{3}$He$^{*} +{}^{4}$He$^{*}$ system, are investigated over a temperature range 1 $μ$K to 1 K. Carefully constructed Born-Oppenheimer molecular potentials are used to describe the electrostatic interaction between the colliding atoms, and complex optical potentials used to represent loss through ionization from the ${}^{1,3}Σ$ states. Magnetic spin-dipole mediated transitions from the ${}^{5}Σ$ state are included and results reported for spin-polarized and unpolarized systems. Comparisons are made with experimental results, previous semi-classical models, and a perturbed single channel model.

physics.atom-ph↗

arXiv2006

Collisional broadening of alkali doublets by helium perturbers

We report results for the Lorentzian profiles of the Li I, Na I and K I doublets and the Na I subordinate doublet broadened by helium perturbers for temperatures up to 3000 K They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali-helium interaction. For all lines except the 769.9 nm K I line, the temperature dependence of the widths over the range 70 < T < 3000 K is accurately represented by the power law form w=aT^b with 0.37 < b < 0.43. The 769.9 K I line has this form for 500 < T < 3000 K with b = 0.49. Although the shifts have a more complex temperature dependence, they all have the general feature of increasing with temperature above T=500 K apart from the 769.9 K I line whose shift decreases with temperature.

physics.atom-ph↗

arXiv2005

Factorization fits to charmless strangeless B decays

We present fits to charmless strangeless hadronic B decay data for mean branching ratios and CP-violating asymmetries using the QCD factorization model of Beneke et al. Apart from one CP-violating parameter, the model gives a very good representation of 26 measured data. We find the CKM angle alpha = (93.5 +/- 8.4 -1.3) degrees and to be quite stable to plausible "charming penguin" corrections.

hep-ph↗

arXiv2003

Factorization fits and the unitarity triangle in charmless two-body B decays

We present fits to charmless hadronic B decay data from the BaBar, Belle and Cleo experiments using two theoretical models: (i) the QCD factorization model of Beneke et al. and (ii) QCD factorization complemented with the so-called charming penguins of Ciuchini et al. When we include the data from pseudoscalar-vector decays the results favor the incorporation of the charming penguin terms. We also fit results for the unitarity triangle parameters and the CP-violating asymmetries.

hep-ph↗

arXiv2003

Factorisation fits and the unitarity triangle

In this paper we present fits to charmless hadronic B decay data from the BaBar, Belle and Cleo experiments using models by Beneke et. al. and Ciuchini et al. When we include the data from pseudo-scalar vector decays (PV) the current experimental results favour the inclusions of a so-called "charming penguin" term. We also present fit results for the Unitary Triangle parameters and the CP violating asymmetries

hep-ph↗

arXiv2003

Purely-long-range bound states of He$(2s ^3S)+$He$(2p ^3P)$

We predict the presence and positions of purely-long-range bound states of $^4$He$(2s ^3S)+{}^4$He$(2p ^3P)$ near the $2s ^3S_1+2p ^3P_{0,1}$ atomic limits. The results of the full multichannel and approximate models are compared, and we assess the sensitivity of the bound states to atomic parameters characterizing the potentials. Photoassociation to these purely-long-range molecular bound states may improve the knowledge of the scattering length associated with the collisions of two ultracold spin-polarized $^4$He$(2s ^3S)$ atoms, which is important for studies of Bose-Einstein condensates.

physics.atom-ph↗

arXiv2002

Factorization and hadronic B decays in the heavy quark limit

Recent theoretical investigations of two-body hadronic B decays have provided justification for the use of the factorization ansatz to evaluate the B decay matrix elements. Motivated by this, we present simplified formulae for a wide range of B decays into the lowest mass pseudoscalar and vector mesons. These formulae, valid in the heavy quark limit, involve a reduced set of soft QCD parameters and, although resulting in some loss of accuracy, should still provide an adequate and transparent tool with which to confront data for some time to come. Finally, we confront these formulae with data on 19 channels.

hep-ph↗

arXiv2001

Ultracold collisions of metastable helium atoms

We report scattering lengths for the singlet Sigma g +, triplet Sigma u + and quintet Sigma g + adiabatic molecular potentials relevant to collisions of two metastable (n=2 triplet S) helium atoms as a function of the uncertainty in these potentials. These scattering lengths are used to calculate experimentally observable scattering lengths, elastic cross sections and inelastic rates for any combination of states of the colliding atoms, at temperatures where the Wigner threshold approximation is valid.

physics.atom-ph↗

arXiv1999

Hadronic B decays: Supersymmetric enhancement and a simple spectator model

Two aspects of hadronic B decays are investigated. Firstly, the supersymmetric enhancement of hadronic b decays by gluino penguin processes is studied through their effect on the Wilson coefficients of the effective Hamiltonian. Secondly, hadronization of the final state quarks is studied through a simple phase space spectator model.

hep-ph↗

arXiv1998

Gluon and gluino penguins and the charmless decays of the b quark

Gluon mediated exclusive hadronic decays of b quarks are studied within the standard model (SM) and the constrained minimally supersymmetric standard model (MSSM). For all allowed regions of the MSSM parameter space (A, tan beta, m_0, m_{1/2}) the penguin magnetic dipole form factor F^R_2 is dominant over the electric dipole and can be larger than the magnetic dipole form factor of the SM. However, overall the SM electric dipole decay amplitude F^L_1 dominates the decay rate. The MSSM penguin contributions to the free quark decay rate approach the 10% level for those regions of parameter space close to the highest allowed values of tan beta (~55) for which the gluino is light (m_{\tilde{g}} \approx 360 GeV) and lies within the range of the six d-squark masses. In these regions the supersymmetric box amplitudes are negligible. The MSSM phases change very little over the allowed parameter space and can lead to significant interference with the SM amplitudes.

hep-ph↗

arXiv1996

The electric dipole moment of the neutron in the constrained minimally supersymmetric standard model

We analyse the electric dipole moment of the neutron in the MSSM, induced by the renormalisation of the soft-susy breaking terms. We run the RGEs using two-loop expressions for gauge and Yukawa couplings and retaining family dependence. The $μ$ and $B$ parameters were determined by minimising the full one-loop Higgs potential, and we find that the neutron EDM lies in the range $10^{-33}<|d_n| < 10^{-29} {\; e\;\mbox{cm}} $.

hep-ph↗

arXiv1992

Spontaneous Baryogenesis in Supersymmetric Models

In this paper we extend the results of previous work on spontaneous baryogenesis to general models involving CP violation in the Higgs sector. We show how to deal with Chern-Simons terms appearing in the effective potential arising from phase changes in the vacuum expectation values of the Higgs fields. In particular, this enables us to apply this mechanism to general supersymmetric models including the minimal supersymmetric standard model, and the extended model with a gauge singlet. A comparison is made between this approach, and that in which one solves the equations of motion for Higgs winding modes. As anticipated in earlier work, the effect of the latter approach is found to be small.

hep-ph↗

arXiv1992

Neutralino Dark Matter in a Class of Unified Theories

The cosmological significance of the neutralino sector is studied for a class of models in which electroweak symmetry breaking is seeded by a gauge singlet. Extensive use is made of the renormalisation group equations to significantly reduce the parameter space, by deriving analytic expressions for all the supersymmetry-breaking couplings in terms of the universal gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the coupling $A$. The composition of the LSP is determined exactly below the W mass, no approximations are made for sfermion masses, and all particle exchanges are considered in calculating the annihilation cross-section; the relic abundance is then obtained by an analytic approximation. We find that in these models, stable neutralinos may make a significant contribution to the dark matter in the universe.

hep-ph↗