arXiv subjects

Ismail Turan

Publications and source records attributed to Ismail Turan.

35 records · Page 2Linked to original sources

arXiv2007

CP Asymmetry in Charged Higgs Decays to Chargino-Neutralino

We analyze the charge-parity (CP) asymmetry in the charged Higgs boson decays to chargino-neutralino pairs, H^- -> chargino_i + neutralino_j. We show first that these modes have a large branching ratio for m_H^- > 600 GeV. We use Cutkosky rules to obtain the analytical formulas needed for the evaluation of the asymmetry under consideration. We then calculate the CP asymmetry in chargino-neutralino decays by including supersymmetric mass bounds, as well as constraints from b -> s gamma, (g-2)_mu, Deltaρand electric dipole moments. Finally, we discuss observability of the asymmetry at the LHC by calculating the number of required charged Higgs events to observe the asymmetry for each decay channel. We show that the inclusion of constraints considerably reduces the projected CP asymmetry, and that the optimal channel for observing the asymmetry is H^- -> chargino_1 + neutralino_2.

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arXiv2007

The Casimir Force in Randall Sundrum Models

We discuss and compare the effects of one extra dimension in the Randall Sundrum models on the evaluation of the Casimir force between two parallel plates. We impose the condition that the result reproduce the experimental measurements within the known uncertainties in the force and the plate separation, and get an upper bound kR < 20 if the curvature parameter k of AdS_5 is equal to the Planck scale. Although the upper bound decreases as k decreases, kR ~ 12, which is the required value for solving the hierarchy problem, is consistent with the Casimir force measurements. For the case where the 5th dimension is infinite, the correction to the Casimir force is very small and negligible.

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arXiv2007

CP Asymmetry in Charged Higgs Decays in MSSM

We discuss and compare the charge-parity (CP) asymmetry in the charged Higgs boson decays H -> \bar{u}_i d_j for the second and third generation quarks in the minimal supersymmetric standard model. As part of the analysis, we derive some general analytical formulas for the imaginary parts of two-point and three-point scalar one-loop integrals and use them for calculating vectorial and tensorial type integrals needed for the problem under consideration. We find that, even though each decay mode has a potential to yield a CP asymmetry larger than 10%, further analysis based on the number of required charged Higgs events at colliders favors the \bar{t}b, \bar{c}b, and \bar{c}s channels, whose asymmetry could reach 10-15% in certain parts of the parameter space.

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arXiv2006

Single Top Production via Gluon Fusion at CERN LHC

We calculate the one-loop flavor violating top quark decay t -> cgg in the Minimal Supersymmetric Standard Model. We discuss the branching ratios obtained with minimal flavor violation, as well as with soft-supersymmetry induced general flavor violation. Based on this rate we calculate the cross section for the single top quark production via gluon fusion, gg -> t cbar, and evaluate its contribution to the cross section for single top quark production in pp collisions at the Large Hadron Collider. We calculate all contributions coming from the standard model and charged Higgs loops, as well as gluino (and neutralino)-up-type squarks, and chargino-down-type squarks loops. Our numerical results show that the gluino and the chargino contributions are largest over the whole parameter range in the unconstrained Minimal Supersymmetric Standard Model. While in general the gluino contributions dominate the cross section, this result depends on the supersymmetric flavor violating parameters in the up and down squark sector, the relative mass of the gauginos, and whether or not the Grand Unified Theory relationships between gaugino masses are satisfied. In the most promising scenarios, the pp -> t cbar + tbar c + X cross section at the Large Hadron Collider can reach a few hundreds fb.

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arXiv2006

Rare Decay of the Top t->c l lbar and Single Top Production at International Linear Collider

We perform a complete and detailed analysis of the flavor changing neutral current rare top quark decays t-> cl+l- and t->c nu_i bar nu_i at one-loop level in the Standard Model, Two Higgs Doublet Models (I and II) and in MSSM. The branching ratios are very small in all models, O(10^-14), except for the case of the unconstrained MSSM, where they can reach O(10^-6) for e+e- and nu_i bar nu_i, and O(10^-5) for tau+ tau-. This branching ratio is comparable to the ones for t-> c V, cH. We also study the production rates of single top and the forward-backward asymmetry in e+e- -> t cbar and comment on the observability of such a signal at the International Linear Collider.

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arXiv2006

The Casimir Force in a Lorentz Violating Theory

We study the effects of the minimal extension of the standard model including Lorentz violation on the Casimir force between two parallel conducting plates in vacuum. We provide explicit solutions for the electromagnetic field using scalar field analogy, for both the cases in which the Lorentz violating terms come from the CPT-even or CPT-odd terms. We also calculate the effects of the Lorentz violating terms for a fermion field between two parallel conducting plates and analyze the modifications of the Casimir force due to the modifications of the Dirac equation. In all cases under consideration, the standard formulas for the Casimir force are modified by either multiplicative or additive correction factors, the latter case exhibiting different dependence on the distance between the plates.

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arXiv2006

Neutralino Dark Matter in the Left-Right Supersymmetric Model

We study the neutralino sector of the left-right supersymmetric model. In addition to the possibilities available in the minimal supersymmetric model, the neutralino states can be superpartners of the U(1)_{B-L} gauge boson, the neutral SU(2)_R neutral gauge boson, or of the Higgs triplets. We analyze neutralino masses and determine the parameter regions for which the lightest neutralino can be one of the new pure states. We then calculate the relic density of the dark matter for each of these states and impose the constraints coming from the rho parameter, the anomalous magnetic moment of the muon, b -> s gamma, as well as general supersymmetric mass bounds. The lightest neutralino can be the bino, or the right-wino, or the neutral triplet higgsino, all of which have different couplings to the standard model particles from the usual neutralinos. A light bino satisfies all the experimental constraints and would be the preferred dark matter candidate for light supersymmetric scalar masses, while the right-wino would be favored by intermediate supersymmetric mass scales. The neutral triplet Higgs fermion satisfies the experimental bounds only in a small region of the parameter space, for intermediate to heavy supersymmetric scalar masses.

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arXiv2006

Rare Decay of the Top t -> cgg in the Standard Model

We calculate the one-loop flavor changing neutral current top quark decay t -> cgg in the Standard Model. We demonstrate that the rate for t -> cgg exceeds the rate for a single gluon emission t -> cg by about two orders of magnitude, while the rate for t -> cq barq (q=u) is slightly smaller than for t -> cg.

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arXiv2005

CP-Odd Phase Effects in a Left-Right Symmetric Chargino Sector

The left-right supersymmetric model contains a right-handed gaugino, as well as several higgsinos, in addition to the minimal supersymmetric model. Thus several CP-noninvariant phases appear in this sector. We analyze their impact on chargino masses and find that only two combinations are physically relevant. We then study the production of charginos in e+e- annihilation and chargino decays into a sneutrino and a lepton, and investigate the effects of CP-phases. We also study the CP-odd asymmetry in the production and subsequent decay at the linear collider with longitudinally polarized beams and find a large enhancement when the decay channel to the right sneutrino is available. The effects of the phases in the left-right supersymmetric chargino sector are different from the minimal supersymmetric standard model, and signals from this sector would be able to distinguish between different gauge symmetries.

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arXiv2005

Width Effects on Near Threshold Decays of the Top Quark t-> cWW,cZZ and of Neutral Higgs Bosons

The nonzero widths of heavy particles become significant when they appear in the final state of any decay occurring just around its kinematical threshold. To take into account such effects, a procedure, called the convolution method, was proposed by Altarelli, Conti and Lubicz. We expand their study which included only threshold effects for t-> bWZ in the standard model. We discuss finite width effects in the three body decays t-> cWW,cZZ and A^0(h^0)->tbW in the type III version of a two Higgs doublet model. In particular, we find a substantial enhancement in the decay t->cZZ, which brings its branching ratio to BR(t->cZZ)~10^-3, and in the decay A^0->tbW, which, unlike the h^0 case, becomes competitive with the A^0 two-body decay modes.

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arXiv2005

t->cg, cγ, cZ in the Left-Right Supersymmetric Model

We analyse top quark flavor violating decays into a charm quark and a gluon, photon or Z boson in a supersymmetric model incorporating left-right symmetry. We include loop calculations involving contributions from scalar quarks, gluinos, charginos and neutralinos. We perform the calculations first assuming the minimal (flavor diagonal) scalar quark scenario, and then allowing for arbitrary mixing between the second and third generation of scalar quarks, in both the up and down sectors. In each case we present separately the contributions from gluino, chargino and neutralino loops and compare their respective strengths. In the flavor-diagonal case, the branching ratio cannot exceed 10^-5 (10^-6) for the gluon (photon/Z boson); while for the unconstrained (flavor non-diagonal) case the same branching ratios can reach almost 10^-4 for the gluon, 10^-6 for the photon and 10^-5 for the Z boson, all of which are slightly below the expected reach of LHC.

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arXiv2005

Neutrino Masses in the Effective Rank-5 Subgroups of E_6 I: Non-supersymmetric Case

The neutral fermion sectors of E_6-inspired low energy models, in particular the Alternative Left-Right and Inert models, are considered in detail within the non-supersymmetric scenario. We show that in their simplest form, these models always predict, for each generation, the lightest neutrino to be an SU(2)_L singlet, as well as two extra neutrinos with masses of the order of the up-quark mass. In order to recover Standard Model phenomenology, additional assumptions in the form of discrete symmetries and/or new interactions are needed. These are classified as the Discrete Symmetry (DS), Higher Dimensional Operators (HDO), and Additional Neutral Fermion (ANF) methods. The DS method can solve the problem, but requires additional Higgs doublets that do not get vacuum expectation values. The HDO method predicts no sterile neutrino, and that the active neutrinos mix with a heavy isodoublet neutrino, thus slightly suppressing the couplings of active neutrinos, with interesting phenomenological implications. The ANF method also predicts this suppression, and also naturally includes one or more "sterile" neutrinos. This scenario allows the existence of sterile neutrino(s) in either a 3+1 or 2+2 structure at low energies, which are favored by the LSND result.

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arXiv2005

Neutrino Masses in the Effective Rank-5 Subgroups of E_6 II: Supersymmetric Case

We present a complete analysis of the neutral fermion sector of supersymmetric E_6-inspired low energy models containing an extra SU(2), concentrating on the Alternate Left-Right and Inert models. We show that the R-parity conserving scenario always exhibits a large Dirac mass for ν_L with maximal mixing with an isosinglet neutrino, and that R-parity violating scenarios do not change the picture other than allowing further mixing with another isosinglet. In order to recover Standard Model phenomenology, additional assumptions in the form of discrete symmetries and/or new interactions are needed. We introduce and investigate Discrete Symmetry method and Higher Dimensional Operators as mechanisms for solving the neutrino mass and mixing problems in these models.

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arXiv2004

The Bounds on Lorentz and CPT Violating Parameters in the Higgs Sector

In this talk, I discuss possible bounds on the Lorentz and CPT violating parameters in the Higgs sector of the so called minimal standard model extension. The main motivation to this study is coming from the fact that unlike the parameters in the fermion and gauge sector, there are no published bounds on the parameters in the Higgs sector. From the one-loop contributions to the photon propagator the bounds on the CPT-even asymmetric coefficients are obtained and the c_μνcoefficients in the fermion sector determine the bound on the CPT-even symmetric coefficients. The CPT-odd coefficient is bounded from the non-zero vacuum expectation value of the Z-boson.

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arXiv2004

Lorentz and CPT Violation in the Higgs Sector

Colladay and Kostelecky have proposed a framework for studying Lorentz and CPT violation in a natural extension of the Standard Model. Although numerous bounds exist on the Lorentz and CPT violating parameters in the gauge boson and fermion sectors, there are no published bounds on the parameters in the Higgs sector. We determine these bounds. The bounds on the CPT-even asymmetric coefficients arise from the one-loop contributions to the photon propagator, those from the CPT-even symmetric coefficients arise from the equivalent c_{μν} coefficients in the fermion sector, and those from the CPT-odd coefficient arise from bounds on the vacuum expectation value of the Z-boson.

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arXiv2004

Universal Extra Dimensions and Kaluza Klein Bound States

We study the bound states of the Kaluza-Klein (KK) excitations of quarks in certain models of Universal Extra Dimensions. Such bound states may be detected at future lepton colliders in the cross section for the pair production of KK-quarks near threshold. For typical values of model parameters, we find that "KK-quarkonia" have widths in the 10 - 100 MeV range, and production cross sections of order a few picobarns for the lightest resonances. Two body decays of the constituent KK-quarks lead to distinctive experimental signatures. We point out that such KK resonances may be discovered before any of the higher KK modes.

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arXiv2003

Mu + N --> Tau + N at a Muon or Neutrino Factory

The experimental discovery of large nu_mu-nu_tau mixing indicates that analogous mixing in the charged lepton sector could be substantial. We consider the possibility that if a high intensity muon beam, perhaps at the early stages of a muon or neutrino factory, strikes a nuclear target, then conversion of some of the muons into tau leptons could occur (similar to the conversion of muons to electrons at MECO). Using current experimental limits on rare tau decays to bound the size of the relevant operators, we find that a 50 GeV muon beam, with 10^20 muons on target per year, could yield as many as 10^7 mu + N --> tau + N events per year. Backgrounds could be substantial, and we comment on the possibility of detection of this process.

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