arXiv subjects

Abdesslam Arhrib

Publications and source records attributed to Abdesslam Arhrib.

At least 91 records · Page 5Linked to original sources

arXiv2006

Charged Higgs Bosons decays H^\pm \to W^\pm (γ, Z) revisited

We study the complete one loop contribution to H^\pm\to W^\pm V, V= Z, γ, both in the Minimal Supersymmetric Standard Model (MSSM) and in the Two Higgs Doublet Model (2HDM). We evaluate the MSSM contributions and compare them with the 2HDM ones taking into account b\to sγconstraint, vacuum stability and unitarity constraints in the case of 2HDM, as well as experimental constraints on the MSSM and 2HDM parameters. In the MSSM, we found that in the intermediate range of \tanβ\la 10 and for large A_t, the branching ratio of H^\pm \to W^{\pm} Z can be of the order 10^{-3} while the branching ratio of H^\pm \to W^{\pm} γis of the order 10^{-5}. We also study the effects of the CP violating phases of Soft SUSY parameters and found that they can modify the branching ratio by about one order of magnitude. However, in the 2HDM where the Higgs sector is less constrained as compared to the MSSM higgs sector, one can reach branching ratio of the order 10^{-2} for both modes.

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arXiv2006

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 $B\to X_sγ$, $B\to X_sl^+l^-$ 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 $b^\prime\to bZ, bH, bg, bγ$, as well as $t^\prime\to tZ,\tH, tg, tγ$. 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.

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arXiv2006

Single Top-Quark Production in Flavor-Changing Z' Models

In some models with an extra U(1) gauge boson Z', the gauge couplings of the Z' to different generations of fermions may not be universal. Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. In this work, we concentrate on the flavor mixing in the up-type quark sector. We deduce a constraint from D0-D0bar mixing. We study in detail single top-quark production via flavor-changing Z' exchange at the LHC and the ILC. We found that for a typical value of M_{Z'}=1 TeV, the production cross section at the LHC can be of the order of 1 fb. However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z' signal unless with a decent charm tagging method. On the other hand, at the ILC, the production cross section at the resonance energy of \sqrt{s} \approx M_{Z'} can reach a size of more than 100 fb. Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb.

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arXiv2005

Complete one--loop analysis to stop and sbottom decays into $Z$ and $W^{\pm}$ bosons

We study radiative corrections to third generation scalar fermions into gauge bosons $Z$ and $W^\pm$. We include both SUSY-QCD, QED and full electroweak corrections. It is found that the electroweak corrections can be of the same order as the SUSY-QCD corrections and interfere destructively in some region of parameter space. The full one loop correction can reach 10% in some SUGRA scenario, while in general MSSM, the one loop correction can reach 20% for large $\tanβ$ and large trilinear soft breaking terms $A_b$.

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arXiv2005

Top and Higgs Flavor Changing Neutral Couplings in two Higgs Doublets Model

We study various channels of top and Higgs Flavor Changing Neutral Couplings (FCNC) in the two Higgs doublet Model with natural flavor conservation (2HDM-I and 2HDM-II). We update known results about t\to c γ, c Z, cg and comment on t\to c h0. The decays $t\to c h0$ as well as {h0,H0}\to \bar{t}c are sensitive both to the bottom Yukawa coupling as well as to the trilinear scalar couplings h0H+H- and H0H+H-. After imposing unitarity constraints as well as vacuum stability conditions on scalar sector parameters, in 2HDM-II we found that for large $\tanβ\ga 40$ and rather light charged Higgs mass $M_{H+}\la 150$ GeV, the maximum values allowed for Br(t\to c h0), {\rm Br}(H0\to \bar{t}c) and {\rm Br}(h0\to \bar{t}c) are: $8\times 10^{-5}$, $10^{-3}$ and $10^{-4}$ respectively. For charged Higgs mass in the range [200,300] GeV, which can accommodate $B\to X_sγ$ constraint if one takes into account large theoretical uncertainties, the branching ratio of both H0\to\bar{t}c and h0\to \bar{t}c can still be slightly larger than $10^{-5}$. For A0\to \bar{t}c, its branching ratio is smaller than $\approx 10^{-7}$ in both 2HDM-I and 2HDM-II. We study also the top-charm associated production at e+e- colliders and its γγoption as well as at muon colliders. It is found that the cross section of γγ\to \bar{t}c can be of the order $0.01\to 0.1$ fb near threshold region, while the cross section of e+e-\to \bar{t}c is well below $10^{-2}$ fb. The situation is slightly better for muon colliders where a few fb cross section can be reached for large \tanβand low center of mass energy \sqrt{s}\la 500 GeV.

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arXiv2005

Third generation sfermions decays into Z and W gauge bosons: full one-loop analysis

The complete one-loop radiative corrections to third generation scalar fermions into gauge bosons Z and W^\pm is considered. We focus on \wt{f}_2 \to Z \wt{f}_1 and \wt{f}_i \to W^\pm \wt{f'}_j (f,f'=t,b). We include both SUSY-QCD, QED and full electroweak corrections. It is found that the electroweak corrections can be of the same order as the SUSY-QCD corrections. The two sets of corrections interfere destructively in some region of parameter space. The full one loop correction can reach 10% in some SUGRA scenario, while in model independent analysis like general MSSM, the one loop correction can reach 20% for large \tanβand large trilinear soft breaking terms A_b.

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arXiv2005

Higgs bosons decay into bottom-strange in two Higgs Doublets Models

We analyze the decays $\{h^0,H^0,A^0\}\to \bar{s}b$ within two Higgs Doublet Models with Natural Flavor Conservation (2HDM) type I and II. It is found that the Higgs bosons decay into bottom-strange can lead to a branching ratio in the range $10^{-5}\to 10^{-3}$ for small $\tanβ\approx 0.1\to 0.5$ and rather light charged Higgs in the 2HDM type I. When $\tanβ\ga 1$, one can easily reach a branching ratio of the order $10^{-5}$. In 2HDM type II, without imposing $b\to sγ$ constraint, the situation is the same as in 2HDM type I. If $b\to sγ$ constraint on charged Higgs mass ($M_{H\pm}\geq 350$ GeV) is imposed, we obtain $Br(h^0 \to \bar{s}b)$ in the range $10^{-5}$--$10^{-6}$. A comparison between the rates of $h^0\to \bar{s}b$ and $h^0\to γγ$ is made. It is found that in the fermiophobic scenario, $h^0\to γγ$ is still the dominant decay mode.

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arXiv2003

Radiative corrections to scalar-fermion pair production in high energy e+e- collisions

We study the one-loop radiative corrections to pair production of the supersymmetric scalar partners of the standard fermions in e+e- annihilation. Both electroweak and SUSY-QCD corrections are considered. Applications are for production of scalar fermions of the third generation, $e^+e^-\to \wt{f}_i \wt{f}_j^*$ (i,j=1,2), $f=t, b,τ$, as well as for production of scalar quarks of the first and second generation. Effects on integrated cross sections are discussed and also the one-loop induced forward-backward asymmetries are studied. It is found that at low energy, \sqrt{s}\approx 500 \to 1000 GeV, the corrections are dominated by the QCD contributions, At high energy, $\sqrt{s}\geq 2$ TeV, the electroweak box diagrams give a substantial contribution and even dominate in some regions of parameters space. The purely loop-induced forward-backward asymmetry can reach values of several per cent.

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arXiv2003

Effect of Fourth Generation CP Phase on b\to s Transitions

We study the effect of a sequential fourth generation on b\to s gamma, B_s mixing, B\to K^{(*)}\ell^+\ell^-, X_s\ell^+\ell^- and ϕK_S, taking into account the presence of a new CP phase in quark mixing. We find that the effects via electromagnetic and strong penguins, such as in b\to s gamma or CP violation in B\to ϕK_S, are rather mild, but impact via box or Z penguins is quite significant. Not only can one have much larger than expected B_s mixing, even if it is measured near the present limit, mixing dependent CP violation could become maximal. For electroweak penguin modes, the fourth generation can provide the enhancement that perhaps may be needed, while the m_{\ell^+\ell^-} dependence of the forward-backward asymmetry in B\to K^{*}\ell^+\ell^- can further probe for the fourth generation. These effects can be studied in detail at the B factories and the Tevatron.

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arXiv2002

CP-odd A^0 production at e^+e^- colliders in MSSM with CP violating phases

We study the production of a heavy CP-odd $A^0$ boson in association with a photon $e^+e^-\to A^0γ$ and a Z boson $e^+e^-\to A^0 Z$ as well as the single production of $A^0$ via $e^+e^- \to ν_e\barν_e A^0$ in the MSSM with CP violating phases. In the case of $e^+e^-\to A^0γ/ A^0 Z$, we show that the squark contribution, which vanishes in the MSSM with real parameters, turns out to be sizeable in presence of CP violating phases in the soft SUSY parameters. For $e^+e^- \to ν_e \barν_e A^0$ in both the 2HDM and MSSM with real parameters, the cross section does not reach observable rates at a NLC. It is found that with a large CP violating phase for $A_t$, cross sections of the order 0.1 fb are attainable for all the processes $e^+e^-\to A^0γ$, $e^+e^-\to A^0 Z$ and $e^+e^- \to ν_e \barν_e A^0$.

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arXiv2002

Single and pair production of MSSM Higgs bosons as a probe of scalar-pseudoscalar mixing at e+e- colliders

We study the associated production of the $A^0$ neutral CP--odd Higgs boson with a neutral gauge boson $Z$ as well as single production of $A^0$ via $e^+e^- \to ν_e {\barν}_e A^0$ at the one loop level in the Minimal Supersymmetric Standard Model (MSSM). We show that the MSSM cross--section may be enhanced by light SUSY particles. Then we study the production processes $e^+e^-\to H^0_iZ$, $H^0_iν_e\bar ν_e$ and $H^0_iH^0_j$ in the context of the MSSM with scalar-pseudoscalar mixing. In a given channel we show that the cross--section for all i (=1,2,3) can be above 0.1 fb provided $M_{H_{2,3}}\la 300$ GeV. This should be detectable at a Next Linear Collider and would provide evidence for scalar--pseudoscalar mixing.

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arXiv2001

Impact of a Light Strange-Beauty Squark on B_s Mixing and Direct Search

If one has Abelian flavor symmetry, $s_R$-$b_R$ mixing could be near maximal. This can drive a "strange-beauty" squark ($\widetilde{sb}_{1}$) to be rather light, but still evade the $b\to sγ$ constraint. Low energy constraints imply that all other superpartners are at TeV scale, except for a possibly light neutralino, $\widetilde χ_1^0$. Whether light or heavy, the $\widetilde{sb}_{1}$ can impact on the $B_s$ system: $Δm_{B_s}$ and indirect CP phase, even for $B_s \to ϕγ$. Direct search is similar to usual $\tilde b \to b\widetilde χ_1^0$, but existing bounds are weakened by $\widetilde{sb}_{1} \to s\widetilde χ_1^0$ possibility. All these effects could be studied soon at the Tevatron.

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arXiv2001

Probing scalar-pseudoscalar mixing in the CP violating MSSM at high-energy $e^+e^-$ colliders

We study the production processes $e^+e^-\to H^0_iZ$, $H^0_iH^0_j$ and $H^0_iν_e\overline ν_e$ in the context of the CP violating MSSM. In a given channel we show that the cross-section for all i (=1,2,3) can be above 0.1 fb provided $M_{H_{2,3}}\la 300$ GeV. This should be detectable at a Next Linear Collider and would provide evidence for scalar-pseudoscalar mixing.

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arXiv2001

Window on Higgs Boson: Fourth Generation $b^\prime$ Decays Revisited

Direct and indirect searches of the Higgs boson suggest that 113 GeV $\lesssim m_H \lesssim$ 170 GeV is likely. With the LEP era over and the Tevatron Run II search via $p\bar p \to WH+X$ arduous, we revisit a case where $WH$ or $ZH +$ jets could arise via strong $b^\prime\bar b^\prime$ pair production. In contrast to 10 years ago, the tight electroweak constraint on $t^\prime$--$b^\prime$ (hence $t^\prime$--$t$) splitting reduces FCNC $b^\prime\to bZ$, $bH$ rates, making $b^\prime\to cW$ naturally competitive. Such a "cocktail solution" is precisely the mix that could evade the CDF search for $b^\prime\to bZ$, and the $b^\prime$ may well be lurking below the top. In light of the Higgs program, this two-in-one strategy should be pursued.

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arXiv2001

Supersymmetric Model Contributions to $B^0_d$--$\bar B^0_d$ Mixing and $B\toππ,ργ$ Decays

Recent results from Belle and BaBar Collaborations hint at a small $\sin2ϕ_1$, while the measured $B\toππ$ rate also seems to be on the low side. Supersymmetric (SUSY) models with down squark mixings can account for the deficits in both cases. By studying the origin of SUSY contributions that could impact on $B^0_d$--$\bar B^0_d$ mixing and $B\toππ$ decay, we find that the former would most likely arise from left-left or right-right squark mixings, while the latter would come from left-right squark mixings. These two processes in general are not much correlated in the Minimum Supersymmetric Standard Model. If the smallness of $B\toππ$ is due to SUSY models, one would likely have large $B\toργ$ from chiral enhancement, and the rate could be within present experimental reach. Even if $B\toργ$ is not greatly enhanced, it could have large mixing dependent CP violation.

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arXiv2001

Two-loop Barr-Zee type Contributions to $(g-2)_μ$ in the MSSM

We consider the contribution of a two-loop Barr-Zee type diagram to $(g-2)_μ$ in the minimal supersymmetric standard model (MSSM). At relatively large $\tanβ$, we show that the contribution of light third generation scalar fermions and neutral CP-even Higgs, $h^0(H^0)$, can easily explain the very recent BNL experimental data. In our analysis $(g-2)_μ$ prefers negative $A_{f}$ and positive $μ$. It is more sensitive to the chirality flipping $h^0(H^0)\wt{f}_R^*\wt{f}_L$ rather than chirality conserving couplings.

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arXiv2000

Unitarity constraints on scalar parameters of the Standard and Two Higgs Doublets Model

Unitarity constraints on the scalar parameters both for the Standard Model and the general Two Higgs Doublet Model (THDM) are examined. In the case of the THDM with an exact discrete symmetry transformation, we show that the mass of the lightest CP-even Higgs boson ($M_h$) and $\tanβ$ are strongly correlated and consequently a strong lower bound can be put on $M_h$ for large $\tanβ$. It is also shown that the inclusion of the discrete symmetry breaking term relaxes the aforementioned correlation.

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arXiv2000

Note on tree-level unitarity in the General Two Higgs Doublet Model

Tree-level unitarity constraints on the masses of the Higgs bosons in the general Two Higgs Doublet Model (THDM) are studied. We first consider the case where the Higgs potential is invariant under a discrete symmetry transformation, and derive strong constraints on the mass of the lightest CP-even Higgs boson ($M_h$) as a function of $\tanβ$. We then show that the inclusion of the discrete symmetry breaking term weakens the mass bounds considerably. It is suggested that a measurement of $M_h$ and $\tanβ$ may enable discrimination between the two Higgs potentials.

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