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F. Boudjema

Publications and source records attributed to F. Boudjema.

At least 73 records · Page 4Linked to original sources
arXiv2003

Full order_alpha electroweak and order alpha_s corrections to e^+e^- --> t t H

We present the full ${\cal O}(α)$ electroweak radiative corrections to associated Higgs top pair production in $e^+e^-$ collisions. We combine these results with a new calculation of the full one-loop QCD corrections. The computation is performed with the help of {\tt GRACE-loop}. We find that the ${\cal O}(α)$ correction can be larger than the ${\cal O}(α_s)$ corrections around the peak of the cross section especially for a light Higgs mass. At threshold these corrections are swamped by the QCD corrections which are enhanced by the gluon Coulomb contribution. We have also subtracted the complete QED corrections and expressed the genuine weak correction both in the $α$-scheme and the $G_μ$-scheme. This reveals that the genuine weak corrections are not negligible and should be taken into account for a precision measurement of this cross section and the extraction of the Yukawa $t \bar t H$ coupling.

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arXiv2002

Full one-loop electroweak radiative corrections to single Higgs production in e+ e-

We present the full ${\cal O}(α)$ electroweak radiative corrections to single Higgs production in \epemt. This takes into account the full one-loop corrections as well as the effects of hard photon radiation. We include both the fusion and Higgs-strahlung processes. The computation is performed with the help of {\tt GRACE-loop} where we have implemented a generalised non-linear gauge fixing condition. The latter includes 5 gauge parameters that can be used for checks on our results. Besides the UV, IR finiteness and gauge parameter independence checks it proves also powerful to test our implementation of the 5-point function. We find that for a 500GeV machine and a light Higgs of mass 150GeV, the total ${\cal O}(α)$ correction is small when the results are expressed in terms of $α_{\rm QED}$. The total correction decreases slightly for higher energies. For moderate centre of mass energies the total ${\cal O}(α)$ decreases as the Higgs mass increases, reaching -10% for $M_H=350$GeV and $\sqrt{s}=500$GeV. In order to quantify the genuine weak corrections we have subtracted the universal virtual and bremsstrahlung correction from the full ${\cal O}(α)$. We find, for $M_H=150$GeV, a weak correction slowly decreasing from -2% to -4% as the energy increases from $\sqrt{s}=300$GeV to $\sqrt{s}=1$TeV after expressing the tree-level results in terms of $G_μ$

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arXiv2002

micrOMEGAs: recent developments

The program micrOMEGAs that calculates the relic density of the lightest supersymmetric particle (LSP) in the MSSM is presented. The impact of coannihilation channels and of higher order corrections to Higgs widths is stressed. The dependence on the RGE code used to calculate the soft parameters is also discussed.

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arXiv2002

Full O(alpha) corrections to e+e- --> nu nu-bar H by GRACE

We present the full O(alpha) corrections to single Higgs production in e+e- collision. The computation is performed with the help of GRACE-LOOP where a generalized non-linear gauge fixing condition is implemented. The numerical results are checked by testing their UV and IR finiteness as well as their independence on all five non-linear gauge parameters. We find that for a 500 GeV collider and a light Higgs boson of mass 150GeV, the total correction is small when the results are expressed in terms of alpha rather than G_mu. For a higher Higgs boson mass of 350GeV, the correction is of order -10%.

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arXiv2002

Invisible Decays of the Supersymmetric Higgs and Dark Matter

We discuss effects of the light sparticles on decays of the lightest Higgs in a supersymmetric model with nonuniversal gaugino masses at the high scale, focusing on the `invisible' decays into neutralinos. These can impact significanlty the discovery possibilities of the lightest Higgs at the LHC. We show that due to these decays, there exist regions of the $M_2-μ$ space where the B.R. $(h \to γγ)$ becomes dangerously low even after imposing the LEP constraints on the sparticle masses, implying a possible preclusion of its discovery in the $γγ$ channel. We find that there exist regions in the parameter space with acceptable relic density and where the ratio ${B.R. (h \to γγ)_{SUSY} \over B.R. (h \to γγ)_{SM}}$ falls below 0.6, implying loss of signal in the $γγ$ channel. These regions correspond to $\tilde χ_1^+, \tilde χ_2^0$ masses which should be accessible already at the Tevatron. Further we find that considerations of relic density put lower limit on the U(1) gaugino mass parameter $M_1$ independently of $μ, \tan β$ and $m_0$.

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arXiv2002

The Higgs Working Group: Summary Report (2001)

Report of the Higgs working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It contains 7 separate sections: A. Theoretical Developments B. Higgs Searches at the Tevatron C. Experimental Observation of an invisible Higgs Boson at LHC D. Search for the Standard Model Higgs Boson using Vector Boson Fusion at the LHC E. Study of the MSSM channel $A/H \to ττ$ at the LHC F. Searching for Higgs Bosons in $t\bar t H$ Production G. Studies of Charged Higgs Boson Signals for the Tevatron and the LHC

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arXiv2002

Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential

We address the issue of the reconstruction of the scalar potential of a two-Higgs doublet model having in mind that of the MSSM. We first consider the general CP conserving dim-4 effective potential. To fully reconstruct this potential, we show that even if all the Higgs masses and their couplings to the standard model particles are measured one needs not only to measure certain trilinear Higgs self-couplings but some of the quartic couplings as well. We also advocate expressing the Higgs self couplings in the mass basis. We show explicitly, that in the so-called decoupling limit, the most easily accessible Higgs self-couplings are given in terms of the Higgs mass while all other dependencies on the parameters of the general effective potential are screened. This helps also easily explain how, in the MSSM, the largest radiative corrections which affect these self couplings are reabsorbed by using the corrected Higgs mass. We also extend our analysis to higher order operators in the effective Higgs potential. While the above screening properties do not hold, we argue that these effects must be small and may not be measured considering the foreseen poor experimental precision in the extraction of the SUSY Higgs self-couplings.

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arXiv2001

micrOMEGAs: A program for calculating the relic density in the MSSM

We present a code that calculates the relic density of the LSP in the MSSM. All tree-level processes for the annihilation of the LSP are included as well as all possible coannihilation processes with neutralinos, charginos, sleptons,squarks and gluinos. In all we have included over 2800 processes not counting charged conjugate states.The cross-sections extracted from CompHEP are calculated exactly. Relativistic formulae for the thermal average are used and care is taken to handle poles and thresholds by adopting specific integration routines. The input parameters can be either the soft SUSY parameters in a general MSSM or the five parameters of a SUGRA model. A link with ISASUGRA/ISAJET allows to calculate the parameters of the MSSM at the weak scale for an input at the GUT scale. The Higgs masses are calculated with FeynHiggsFast. Routines calculating g-2 and bsgamma are also included.

hep-ph↗
arXiv2001

The MSSM invisible Higgs in the light of dark matter and g-2

Giving up the assumption of the gaugino mass unification at the GUT scale, the latest LEP and Tevatron data still allow the lightest supersymmetric Higgs to have a large branching fraction into invisible neutralinos. Such a Higgs may be difficult to discover at the LHC and is practically unreachable at the Tevatron. We argue that, for some of these models to be compatible with the relic density, light sleptons with masses not far above the current limits are needed. There are however models that allow for larger sleptons masses without being in conflict with the relic density constraint. This is possible because these neutralinos can annihilate efficiently through a Z-pole. We also find that many of these models can nicely account, at the 2σlevel, for the discrepancy in the latest g-2 measurement. However, requiring consistency with the g-2 at the 1σlevel, excludes models that lead to the largest Higgs branching fraction into LSP's. In all cases one expects that even though the Higgs might escape detection, one would have a rich SUSY phenomenology even at the Tevatron, through the production of charginos and neutralinos.

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arXiv2000

The Higgs Working Group: Summary Report

Report of the Higgs working group for the Workshop "Physics at TeV Colliders", Les Houches, France 8-18 June 1999. It contains 6 separate sections: 1. Measuring Higgs boson couplings at the LHC. 2. Higgs boson production at hadron colliders at NLO. 3. Signatures of Heavy Charged Higgs Bosons at the LHC. 4. Light stop effects and Higgs boson searches at the LHC. 5. Double Higgs production at TeV Colliders in the MSSM. 6. Programs and Tools for Higgs Bosons.

hep-ph↗
arXiv2000

SUSY Higgs at the LHC: Effects of light charginos and neutralinos

In view of the latest LEP data we consider the effects of charginos and neutralinos on the two-photon and bbbar signatures of the Higgs at the LHC. Assuming the usual GUT inspired relation between M_1 and M_2 we show that there are only small regions with moderate tanbeta and large stop mixings that may be dangerous. Pathological models not excluded by LEP which have degeneracy between the sneutrino and the chargino are however a real danger because of large branching fraction of the Higgs into invisibles. We have also studied models where the gaugino masses are not unified at the GUT scale. We take M_1=M_2/10 as an example where large reductions in the signal at the LHC can occur. However we argue that such models with a very light neutralino LSP may give a too large relic density unless the sleptons are light. We then combine this cosmological constraint with neutralino production with light sfermions to further reduce the parameter space that precludes observability of the Higgs at the LHC. We still find regions of parameter space where the drops in the usual Higgs signals at the LHC can be drastic. Nonetheless, in such scenarios where Higgs may escape detection we show that one should be able to produce all charginos and neutralinos. Although the heavier of these could cascade into the Higgs, the rates are not too high and the Higgs may not always be recovered this way.

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arXiv1999

Bosonic Quartic Couplings at LEP2

We list the set of C and P conserving anomalous quartic vector bosons self-couplings which can be tested at LEP2 through triple vector boson production. We show how this set can be embedded in manifestly SU(2)xU(1) gauge invariant operators exhibiting an SU(2)_c global symmetry. We derive bounds on these various couplings and show the most relevant distributions that can enhance their contribution. We also find that an e+e- collider running at 500 GeV can improve the LEP2 limits by as much as three orders of magnitude.

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arXiv1999

Implementation of the Non-Linear Gauge into GRACE

A general non-linear gauge condition is implemented into GRACE, an automated system for the calculation of physical processes in high-energy physics. This new gauge-fixing is used as a very efficient means to check the results of large scale evaluation in the standard model computed automatically. We report on some systematic test-runs which have been performed for one-loop two-to-two processes to show the validity of the gauge check.

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arXiv1999

Z radiation off stops at a linear collider

We calculate e+e- --> stop/stop/Z at a linear collider. For large splitting between the two stops the cross-section is sensitive to the value of m(stop2) when this particle is too heavy to be directly produced. The results are compared to e+e- --> stop/stop/h.

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arXiv1999

SUSY Higgs at the LHC: Large stop mixing effects and associated production

We revisit the effect of the large stop mixing on the decay and production of the lightest SUSY Higgs at the LHC. We stress that whenever the inclusive 2-photon signature is substantially reduced, associated production, $Wh$ and $t\bar t h$, with the subsequent decay of the Higgs into photons is enhanced and becomes an even more important discovery channel. We also point out that these reductions in the inclusive channel do not occur for the smallest Higgs mass where the significance is known to be lowest. We show that in such scenarios the Higgs can be produced in the decay of the heaviest stop. For not too heavy masses of the pseudo-scalar Higgs where the inclusive channel is even further reduced, we show that large stop mixing also allows the production of the pseudo-scalar Higgs through stop decays. These large mixing scenarios therefore offer much better prospects than previously thought. As a by-product we have recalculated stop1-stop1-h production at the LHC and give a first evaluation of stop1-stop1-Z.

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arXiv1998

Associated stop Higgs Production at the Linear Collider and Extraction of the stop Parameters

We calculate stop stop Higgs production at the linear collider. Combining the measurements from the pair production of the lightest stop and that of the mass of the Higgs we show how, in a scenario where only the lightest stop and the lightest Higgs were accessible, one could extract the mass of the heavier stop and infer some useful information on the SUSY parameters.

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arXiv1998

Minimal Ten-parameter Hermitian Texture Zeroes Mass Matrices and the CKM Matrix

Hermitian mass matrices for the up and down quarks with texture zeroes but with the minimum number of parameters, ten, are investigated. We show how these {\em minimum parameter} forms can be obtained from a general set of hermitian matrices through weak basis transformations. For the most simple forms we show that one can derive exact and compact parametrizations of the CKM mixing matrix in terms of the elements of these mass matrices (and the quark masses).

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