New bounds on slepton and Wino masses in anomaly mediated supersymmetry breaking models

Supersymmetry (SUSY), if it exists, must be broken, and this breaking cannot take place in the observable sector (OS). Thus one envisages a hidden sector (HS), whose fields are all singlets under the SM gauge group, where SUSY is broken. The key question is how to convey the breaking to the OS. One option is to consider a contact interaction between the HS and the OS fields in the Kahler potential, suppressed by the Planck mass squared. This tree-level interaction induces SUSY breaking in the OS; such models are generically known as supergravity (SUGRA) type models, where the gravitino mass is of the order of 1 TeV. Recently, one came to note that if the OS and the HS live in two distinct 3-branes separated by a finite distance along a fifth compactified dimension, there is no tree-level term in the Kahler potential that transmit SUSY breaking from the HS to the OS. However, a superconformal anomaly may induce the SUSY breaking in the OS (this term is present in the SUGRA type models too, but is suppressed in comparison to the usual softbreaking terms). To generate the weak scale masses of the sparticles, the gravitino mass must be of the order of tens of TeV. Such models are generically known as anomaly-mediated SUSY breaking (AMSB) models [5,6]. AMSB, alongwith the radiative electroweak symmetry breaking condition, should fix the sparticle spectrum completely in terms of three parameters: m3/2 (the mass of the fermionic component of the compensator superfield, and equal to the gravitino mass), tan β (ratio of the vacuum expectation values (VEV) of the two Higgs fields), and sign(� ). The gaugino masses M1, M2 and M3, and the trilinear couplings (generically denoted by A) can be obtained from the relevant renormalization group (RG) β-functions and anomalous dimensions. The sfermion masses, as well as the Higgs mass parameters, are also determined by m3/2; unfortunately, for sfermions that do not couple to asymptotically free gauge groups (i.e., both right and left sleptons), the masses come out to be tachyonic. The remedy is sought by putting a positive definite mass squared term m 2 in the GUT scale boundary conditions. This is not exactly an ad hoc prescription; there are a number of physical motivations for the introduction of such a term, mostly related to the presence of extra field(s) in the bulk. Such models with a universal m0 for all scalars are called the minimal AMSB (mAMSB) models [5,6]. The phenomenology of such models has been at the focus of attention of many recent works [7–12], and we also confine our discussions within the scope of mAMSB models. With four free parameters in the model, one can determine the complete particle spectrum. A few key observations can be immediately made [5–9]: (i) The lighter chargino ˜ χ ± is almost degenerate with the