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K. Benakli

Publications and source records attributed to K. Benakli.

At least 19 recordsLinked to original sources
arXiv2014

The Constrained Minimal Dirac Gaugino Supersymmetric Standard Model

We examine the possibilities for constructing models with Dirac gaugino masses and unification of gauge couplings. We identify one promising model, and discuss to what extent it can have a "natural SUSY" spectrum. We then determine the low-energy constraints upon it, and propose a constrained set of boundary conditions at the unification scale. We describe the implementation of these boundary conditions in the spectrum-generator generator \SARAH and we perform a first exploration of the parameter space, specifically searching for points where the spectrum is relatively light. It is shown that the pattern of the masses of SUSY states is very different compared to any expectations from the constrained MSSM.

hep-ph↗
arXiv2012

One-loop adjoint masses for branes at non-supersymmetric angles

This proceeding is based on arXiv:1105.0591 [hep-th] where we consider breaking of supersymmetry in intersecting D-brane configurations by slight deviation of the angles from their supersymmetric values. We compute the masses generated by radiative corrections for the adjoint scalars on the brane world-volumes. In the open string channel, the string two-point function receives contributions only from the infrared limits of N~4 and N~2 supersymmetric configurations, via messengers and their Kaluza-Klein excitations, and leads at leading order to tachyonic directions.

hep-th↗
arXiv2011

One-loop adjoint masses for non-supersymmetric intersecting branes

We consider breaking of supersymmetry in intersecting D-brane configurations by slight deviation of the angles from their supersymmetric values. We compute the masses generated by radiative corrections for the adjoint scalars on the brane world-volumes. In the open string channel, the string two-point function receives contributions only from the infrared and the ultraviolet limits. The latter is due to tree-level closed string uncanceled NS-NS tadpoles, which we explicitly reproduce from the effective Born-Infeld action. On the other hand, the infrared region reproduces the one-loop mediation of supersymmetry breaking in the effective gauge theory, via messengers and their Kaluza-Klein excitations. In the toroidal set-up considered here, it receives contributions only from broken N=4 and N=2 supersymmetric configurations, and thus always leads at leading order to a tachyonic direction, in agreement with effective field theory expectations.

hep-th↗
arXiv2010

Dirac Gauginos in General Gauge Mediation

We extend the formulation by Meade, Seiberg and Shih of general gauge mediation of supersymmetry breaking to include Dirac masses for the gauginos. These appear through mixing of the visible sector gauginos with additional states in adjoint representations. We illustrate the method by reproducing the existing results in the literature for the gaugino and sfermion masses when preserving R-symmetry. We then explain how the generation of same sign masses for the two propagating degrees of freedom in the adjoint scalars can be achieved. We end by commenting on the use of the formalism for describing U(1) mixing.

hep-ph↗
arXiv2010

Dirac Gauginos, Gauge Mediation and Unification

We investigate the building of models with Dirac gauginos and perturbative gauge coupling unification. Here, in contrast to the MSSM, additional fields are required for unification, and these can naturally play the role of the messengers of supersymmetry breaking. We present a framework within which such models can be constructed, including the constraints that the messenger sector must satisfy; and the renormalisation group equations for the soft parameters, which differ from those of the MSSM. For illustration, we provide the spectrum at the electroweak scale for explicit models whose gauge couplings unify at the scale predicted by heterotic strings.

hep-ph↗
arXiv2010

Dirac Gauginos and Kinetic Mixing

We present formulae for the calculation of Dirac gaugino masses at leading order in the supersymmetry breaking scale using the methods of analytic continuation in superspace and demonstrate a link with kinetic mixing, even for non-abelian gauginos. We illustrate the result through examples in field and string theory. We discuss the possibility that the singlet superfield that gives the U(1) gaugino a Dirac mass may be a modulus, and some consequences of the D-term coupling to the scalar component. We give examples of possible effects in colliders and astroparticle experiments if the modulus scalar constitutes decaying dark matter.

hep-ph↗
arXiv2009

Dark Matter with Dirac and Majorana Gaugino Masses

We consider the minimal supersymmetric extension of the Standard Model allowing both Dirac and Majorana gauginos. The Dirac masses are obtained by pairing up extra chiral multiplets: a singlet S for U(1)_Y, a triplet T for SU(2) and an octet O for SU(3) with the respective gauginos. The electroweak symmetry breaking sector is modified by the couplings of the new fields S and T to the Higgs doublets. We discuss two limits: i) both the adjoint scalars are decoupled with the main effect being the modification of the Higgs quartic coupling; ii) the singlet remaining light, and due to its direct coupling to sfermions, providing a new contribution to the soft masses and inducing new decay/production channels. We discuss the LSP in this scenario; after mentioning the possibility that it may be a Dirac gravitino, we focus on the case where it is identified with the lightest neutralino, and exhibit particular values of the parameter space where the relic density is in agreement with WMAP data. This is illustrated for different scenarios where the LSP is either a bino (in which case it can be a Dirac fermion) or bino-higgsino/wino mixtures. We also point out in each case the peculiarity of the model with respect to dark matter detection experiments.

hep-ph↗
arXiv2008

Physics Beyond the Standard Model: Supersymmetry

This collection of studies on new physics at the LHC constitutes the report of the supersymmetry working group at the Workshop `Physics at TeV Colliders', Les Houches, France, 2007. They cover the wide spectrum of phenomenology in the LHC era, from alternative models and signatures to the extraction of relevant observables, the study of the MSSM parameter space and finally to the interplay of LHC observations with additional data expected on a similar time scale. The special feature of this collection is that while not each of the studies is explicitely performed together by theoretical and experimental LHC physicists, all of them were inspired by and discussed in this particular environment.

hep-ph↗
arXiv2007

A New Gauge Mediation Theory

We propose a class of models with gauge mediation of supersymmetry breaking, inspired by simple brane constructions, where R-symmetry is very weakly broken. The gauge sector has an extended N=2 supersymmetry and the two electroweak Higgses form an N=2 hypermultiplet, while quarks and leptons remain in N=1 chiral multiplets. Supersymmetry is broken via the D-term expectation value of a secluded U(1) and it is transmitted to the Standard Model via gauge interactions of messengers in N=2 hypermultiplets: gauginos thus receive Dirac masses. The model has several distinct experimental signatures with respect to ordinary models of gauge or gravity mediation realizations of the Minimal Supersymmetric Standard Model (MSSM). First, it predicts extra states as a third chargino that can be observed at collider experiments. Second, the absence of a D-flat direction in the Higgs sector implies a lightest Higgs behaving exactly as the Standard Model one and thus a reduction of the `little' fine-tuning in the low tan(beta) region. This breaking of supersymmetry can be easily implemented in string theory models

hep-ph↗
arXiv2006

Les Houches "Physics at TeV Colliders 2005'' Beyond the Standard Model working group: summary report

The work contained herein constitutes a report of the "Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. We present reviews of current topics as well as original research carried out for the workshop. Supersymmetric and non-supersymmetric models are studied, as well as computational tools designed in order to facilitate their phenomenology.

hep-ph↗
arXiv2005

Split extended supersymmetry from intersecting branes

We study string realizations of split extended supersymmetry, recently proposed in hep-ph/0507192. Supersymmetry is broken by small ($ε$) deformations of intersection angles of $D$-branes giving tree-level masses of order $m_0^2\sim εM_s^2$, where $M_s$ is the string scale, to localized scalars. We show through an explicit one-loop string amplitude computation that gauginos acquire hierarchically smaller Dirac masses $m_{1/2}^D \sim m_0^2/M_s$. We also evaluate the one-loop Higgsino mass, $μ$, and show that, in the absence of tree-level contributions, it behaves as $μ\sim m_0^4/M_s^3$. Finally we discuss an alternative suppression of scales using large extra dimensions. The latter is illustrated, for the case where the gauge bosons appear in N=4 representations, by an explicit string model with Standard Model gauge group, three generations of quarks and leptons and gauge coupling unification.

hep-th↗
arXiv2005

Kaluza-Klein states at the LHC in models with localized fermions

We give a brief review of some aspects of physics with TeV size extra-dimensions. We focus on a minimal model with matter localized at the boundaries for the study of the production of Kaluza-Klein excitations of gauge bosons. We briefly discuss different ways to depart from this simple analysis.

hep-ph↗
arXiv2003

Brane to bulk supersymmetry breaking and radion force at micron distances

We study mediation of supersymmetry breaking in the bulk, in models with primordial supersymmetry breaking on D-branes at the string scale, in the TeV region. We compute the gravitino and scalar masses up to one-loop level, as well as the radion coupling to matter. We find that the latter mediates a model independent force at submillimeter distances that can be tested in micro-gravity experiments for any dimensionality of the bulk. In the case of two large dimensions, our type I string framework provides an example which allows to stabilize the radion potential and determine the desired hierarchy between the string and Planck scales.

hep-ph↗
arXiv2001

D-brane Models with Non-Linear Supersymmetry

We study a class of type I string models with supersymmetry broken on the world-volume of some D-branes and vanishing tree-level potential. Despite the non-supersymmetric spectrum, supersymmetry is non-linearly realized on these D-branes, while it is spontaneously broken in the bulk by Scherk-Schwarz boundary conditions. These models can easily accommodate 3-branes with interesting gauge groups and chiral fermions. We also study the effective field theory and in particular we compute the four-fermion couplings of the localized Goldstino with the matter fermions on the brane.

hep-th↗
arXiv2001

Finite Higgs mass without Supersymmetry

We identify a class of chiral models where the one-loop effective potential for Higgs scalar fields is finite without any requirement of supersymmetry. It corresponds to the case where the Higgs fields are identified with the components of a gauge field along compactified extra dimensions. We present a six dimensional model with gauge group U(3)xU(3) and quarks and leptons accomodated in fundamental and bi-fundamental representations. The model can be embedded in a D-brane configuration of type I string theory and, upon compactification on a T^2/Z_2 orbifold, it gives rise to the standard model with two Higgs doublets.

hep-th↗
arXiv2000

Contact interactions in D-brane models

We compute the tree-level four-point scattering amplitudes in string models where matter fields live on D-brane intersections. Extracting the contribution of massless modes, we are left with dimension-six four-fermion operators which in general receive contributions from three different sources: exchange of massive Kaluza--Klein excitations, winding modes and string oscillator states. We compute their coefficients and extract new bounds on the string scale in the brane-world scenario. This is contrasted with the situation where matter fields arise from open strings with both ends confined on the same collection of D-branes, in which case the exchange of massive string modes leads to dimension-eight operators that have been studied in the past. When matter fields live on brane intersections, the presence of dimension-six operators increases the lower bound on the string scale to 2--3 TeV, independently of the number of large extra dimensions.

hep-th↗
arXiv2000

Large Dimensions and String Physics in Future Colliders

We review the status of low-scale string theories and large extra-dimensions. After an overview on different string realizations, we discuss some of the main important problems and we summarize present bounds on the size of possible extra-dimensions from collider experiments.

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