arXiv subjects

S. Recksiegel

Publications and source records attributed to S. Recksiegel.

At least 19 recordsLinked to original sources

arXiv2016

Relic density of wino-like dark matter in the MSSM

The relic density of TeV-scale wino-like neutralino dark matter in the MSSM is subject to potentially large corrections as a result of the Sommerfeld effect. A recently developed framework enables us to calculate the Sommerfeld-enhanced relic density in general MSSM scenarios, properly treating mixed states and multiple co-annihilating channels as well as including off-diagonal contributions. Using this framework, including on-shell one-loop mass splittings and running couplings and taking into account the latest experimental constraints, we perform a thorough study of the regions of parameter space surrounding the well known pure-wino scenario: namely the effect of sfermion masses being non-decoupled and of allowing non-negligible Higgsino or bino components in the lightest neutralino. We further perform an investigation into the effect of thermal corrections and show that these can safely be neglected. The results reveal a number of phenomenologically interesting but so far unexplored regions where the Sommerfeld effect is sizeable. We find, in particular, that the relic density can agree with experiment for dominantly wino neutralino dark matter with masses ranging from 1.7 to beyond 4 TeV. In light of these results the bounds from Indirect Detection on wino-like dark matter should be revisited.

hep-ph↗

arXiv2010

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetric-energy $e^+e^-$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{-2}$s$^{-1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.

hep-ex↗

arXiv2008

Measuring B -> tau nu and B_c -> tau nu at the Z peak

The measurement of B->tau nu at the B factories provides important constraints on the parameter tan beta/m_H^+- in the context of models with two Higgs doublets. Limits on this decay from e+e- collisions at the Z peak were sensitive to the sum of B->tau nu and B_c->tau nu. Due to the possibly sizeable contribution from B_c->tau nu we suggest that a signal for this combination might be observed if the LEP L3 Collaboration used their total data of ~3.6 10^6 hadronic decays of the Z boson. Moreover, we point out that a future Linear Collider operating at the Z peak (Giga Z option) could constrain tan beta/m_H^+- from the sum of these processes with a precision comparable to that anticipated at proposed high luminosity B factories from B-> tau nu alone.

hep-ph↗

arXiv2008

B, D and K decays

With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.

hep-ph↗

arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗

arXiv2004

Fine and Hyperfine Splittings of Charmonium and Bottomonium: An Improved Perturbative QCD Approach

We extend the formalism based on perturbative QCD that was developed in our previous work, and compute the hyperfine splittings of the bottomonium spectrum as well as the fine and hyperfine splittings of the charmonium spectrum. All the corrections up to O(alpha_s^5 m) are included in the computations. We find agreement (with respect to theoretical uncertainties) with the experimental values whenever available and give predictions for not yet observed splittings.

hep-ph↗

arXiv2003

Comparing the QCD potential in Perturbative QCD and Lattice QCD at large distances

We compare the perturbatively calculated QCD potential to that obtained from lattice calculations in the theory without light quark flavours. We examine E_tot(r) = 2 m_pole + V_QCD(r) by re-expressing it in the MSbar mass m = m^MSbar(m^MSbar) and by choosing specific prescriptions for fixing the scale mu (dependent on r and m). By adjusting m so as to maximise the range of convergence, we show that perturbative and lattice calculations agree up to 3*r_0 ~ 7.5 GeV^-1 (r_0 is the Sommer scale) within the uncertainty of order Lambda^3 r^2.

hep-ph↗

arXiv2003

The effect of H^\pm on B^\pm -> τ^\pm νand B^\pm -> μ^\pm ν

The hitherto unobserved purely leptonic decays B^\pm -> τ^\pm νand B^\pm -> μ^\pm νare of much interest at current and future runs of the e+e- B factories. Such decays are sensitive to charged Higgs bosons (H^\pm) at the tree-level and provide essentially model independent constraints on \tanβ/m_{H^\pm}. We include the large corrections to the H^\pm-ub coupling induced by virtual SUSY effects and show that the bounds on \tanβ/m_{H^\pm} can be significantly weakened or strengthened.

hep-ph↗

arXiv2002

Improved Perturbative QCD Approach to the Bottomonium Spectrum

Recently it has been shown that the gross structure of the bottomonium spectrum is reproduced reasonably well within the non-relativistic boundstate theory based on perturbative QCD. In that calculation, however, the fine splittings and the S-P level splittings are predicted to be considerably narrower than the corresponding experimental values. We investigate the bottomonium spectrum within a specific framework based on perturbative QCD, which incorporates all the corrections up to O(alpha_S^5 m_b) and O(alpha_S^4 m_b), respectively, in the computations of the fine splittings and the S-P splittings. We find that the agreement with the experimental data for the fine splittings improves drastically due to an enhancement of the wave functions close to the origin as compared to the Coulomb wave functions. The agreement of the S-P splittings with the experimental data also becomes better. We find that natural scales of the fine splittings and the S-P splittings are larger than those of the boundstates themselves. On the other hand, the predictions of the level spacings between consecutive principal quantum numbers depend rather strongly on the scale mu of the operator \propto C_A/(m_b r^2). The agreement of the whole spectrum with the experimental data is much better than the previous predictions when mu \simeq 3-4 GeV for alpha_S(M_Z)=0.1181. There seems to be a phenomenological preference for some suppression mechanism for the above operator.

hep-ph↗

arXiv2002

Large enhancement of D -> e nu and Ds -> e nu in R Parity violating SUSY models

The purely leptonic decays D -> e nu and Ds -> e nu, for which no experimental limits exist, are highly suppressed in the Standard Model. Mere observation of these decays at the B factories BELLE/BaBar or forthcoming CLEO-c would be a clear signal of physics beyond the SM. We show that R parity violating slepton contributions can give rise to spectacular enhancements of the decay rates, resulting in branching ratios as large as 5 x 10^-3, which strongly motivates a search in these channels.

hep-ph↗

arXiv2002

Purely Leptonic B decays at High Luminosity e+e- B factories

High Luminosity upgrades of the KEK-B collider are being discussed. We consider the role of the purely leptonic decays B^\pm -> l^\pm nu and B^0 -> l+l- in motivating such an upgrade. These decays are very sensitive to R parity violating extensions of the MSSM, and we show that future runs of the KEK-B factory can be competitive with high energy colliders for probing such models.

hep-ph↗

arXiv2002

R Parity violating enhancement of Bu -> l nu and Bc -> l nu

We study the decays Bu -> l nu and Bc -> l nu in the context of the Minimal Supersymmetric Standard Model (MSSM) with explicit R parity violation. We analyse the correlation between the two decays and show that branching ratios (BRs) for Bc -> l nu may be of order 5% (over 40% in one case), without violating current bounds on Bu -> l nu. Although Bc mesons are inaccessible at the e+e- B factories, such large BRs for Bc -> l nu would possibly be within experimental observability at LEP and the Tevatron Run II, with much larger yields expected at the hadronic B factories. We also update some earlier bounds on products of R parity violating couplings in the light of new experimental results.

hep-ph↗

arXiv2002

Direct CP asymmetry of b -> s gamma and b -> d gamma in models beyond the Standard Model

We study the direct CP asymmetry of the decays b -> s gamma and b -> d gamma in the context of two models: i) a supersymmetric (SUSY) model with unconstrained SUSY phases, and ii) a model with a single generation of vector quarks. In both the above models we show that b -> d gamma can sizeably influence the combined asymmetry (i.e. that of a sample containing both b -> s gamma and b -> d gamma), and in case (ii) may in fact be the dominant contribution.

hep-ph↗

arXiv2001

Direct CP Asymmetry of B -> X_d,s γin a model with Vector quarks

We investigate the effect of vector quarks on the inclusive decays B -> X_d,s γ. We show that the branching ratio of B -> X_d γcan differ sizably from the SM and MSSM predictions, being enhanced to present experimental observability or suppressed such that present runs of the B factories would not observe it. Current measurements of the direct CP asymmetry (A_CP) for B -> X_s γare sensitive to the contribution from B -> X_d γ. For a sufficiently enhanced BR(B -> X_d γ) we show that the dominant contribution to the combined asymmetry may be from B -> X_d γ. Thus any large value for A_CP should not immediately be attributed to B -> X_s γ, which stresses the importance of good K/pi separation.

hep-ph↗

arXiv2001

Perturbative QCD Potential, Renormalon Cancellation and Phenomenological Potentials

We examine the total energy E_tot(r) = 2 m_pole + V_QCD(r) of the b\bar b system within perturbative QCD up to O(α_S^3). We extend a previous analysis by incorporating effects of the non-zero charm-quark mass in loops. We find that, once the renormalon cancellation is performed, E_tot(r) agrees well with typical phenomenological potentials for heavy quarkonia at distances 0.5 GeV^-1 ~< r ~< 3 GeV^-1. We also examine the perturbative predictions for E_tot(r) of other heavy quarkonium systems. Whenever stable predictions are obtained, they agree with each other up to an r-independent constant.

hep-ph↗

arXiv2001

Direct CP Asymmetry of B -> X_d γin the effective SUSY model

We investigate the effect of supersymmetric CP violating phases on the inclusive decay B\to X_dγ. Although such a decay contains a large background from B\to X_sγ, if isolated it may exhibit sizeable CP violation, both in the Standard Model (SM) and in the context of models beyond the SM. With unconstrained supersymmetric CP violating phases we show that the direct CP asymmetry (A_CP) lies in the region -40% \le A_CP \le 40%, where a positive asymmetry would constitute a clear signal of physics beyond the SM. Even if a direct measurement of B\to X_dγproves too dif ficult experimentally, its asymmetry contributes non-negligibly to the measurements of A_CP for B\to X_sγ, and thus should be included in future analyses. We show t hat there may be both constructive and destructive interference between A^dγ_CP and A^sγ_CP.

hep-ph↗

arXiv2001

Effect of Supersymmetric phases on the Direct CP Asymmetry of B -> X_d γ

hep-ph↗

arXiv1999

Comparing B -> X_u l nu_l to B -> X_s gamma

We suggest a method to determine V_ub / V_ts through a comparison of B -> X_u l nu_l and B -> X_s gamma. The relevant quantity is the spectrum of the light-cone component of the final state hadronic momentum, which in B -> X_s gamma is the photon energy while in B -> X_u l nu_l this requires a measurement of both hadronic energy and hadronic invariant mass. The non-perturbative contributions at tree level to these distributions are identical and may be cancelled by taking the ratio of the spectra. Radiative corrections to this comparison are discussed to order alpha_s and are combined with the non-perturbative contributions.

hep-ph↗