document: anomaly - mediated supersymmetry breaking ( amsb ) models have received much attention in the literature due to their attractive properties@xcite : the soft supersymmetry ( susy ) breaking terms are completely calculable in terms of just one free parameter ( the gravitino mass , @xmath11 ) , the soft terms are real and flavor invariant , thus solving the susy flavor and @xmath12 problems , the soft terms are actually renormalization group invariant@xcite , and can be calculated at any convenient scale choice . in order to realize the amsb set - up , the hidden sector must be `` sequestered '' on a separate brane from the observable sector in an extra - dimensional universe , so that tree - level supergravity breaking terms do not dominate the soft term contributions . 
   such a set - up can be realized in brane - worlds , where susy breaking takes place on one brane , with the visible sector residing on a separate brane . 
   the soft susy breaking ( ssb ) terms arise from the rescaling anomaly .    in spite of its attractive features , 
   amsb models suffer from the well - known problem that slepton mass - squared parameters are found to be negative , giving rise to tachyonic states . the original solution to this problem 
   is to suppose that scalars acquire as well a universal mass @xmath13 , which when added to the amsb ssb terms , renders them positive . 
   thus , the parameter space of the `` minimal '' amsb model ( mamsb ) is given by m_0 ,  m_3/2 ,  ,  sign ( ) . 
   an alternative set - up for amsb has been advocated in ref . 
   @xcite , known as hypercharged anomaly - mediation ( hcamsb ) . 
   it is a string motivated scenario which uses a similar setup as the one envisioned for amsb . in hcamsb , 
   susy breaking is localized at the bottom of a strongly warped hidden region , geometrically separated from the visible region where the mssm resides . 
   the warping suppresses contributions due to tree - level gravity mediation@xcite and the anomaly mediation@xcite can become the dominant source of susy breaking in the visible sector . 
   possible exceptions to this sequestering mechanism are gaugino masses of @xmath14 gauge symmetries  @xcite . 
   thus , in the mssm , the mass of the bino the gaugino of @xmath15 can be the only soft susy breaking parameter not determined by anomaly mediation@xcite . depending on its size 
   , the bino mass @xmath16 can lead to a small perturbation to the spectrum of anomaly mediation , or it can be the largest soft susy breaking parameter in the visible sector : as a result of rg evolution its effect on other soft susy breaking parameters can dominate the contribution from anomaly mediation . in extensions of the mssm , additional @xmath17s can also communicate susy breaking to the mssm sector  @xcite . 
   besides sharing the same theoretical setup , anomaly mediation and hypercharge mediation cure phenomenological shortcomings of each other . 
   the minimal amsb model predicts a negative mass squared for the sleptons ( and features relatively heavy squarks ) . on the other hand , 
   the pure hypercharge mediation suffers from negative squared masses for stops and sbottoms ( and features relatively heavy sleptons ) : see sec . 
   [ sec : pspace ] . as a result 
   , the combination of hypercharge and anomaly mediation leads to phenomenologically viable spectra for a sizable range of relative contributions  @xcite . 
   we parametrize the hcamsb ssb contribution @xmath18 using a dimensionless quantity @xmath2 such that @xmath19 so that @xmath2 governs the size of the hypercharge contribution to soft terms relative to the amsb contribution . 
   then the parameter space of hcamsb models is given by ,  m_3/2 ,  ,  sign ( ) . in the hcamsb model , we assume as usual that electroweak symmetry is broken radiatively by the large top - quark yukawa coupling . then the ssb @xmath20 term and the superpotential @xmath21 term are given as usual by the scalar potential minimization conditions which emerge from requiring an appropriate breakdown of electroweak symmetry . 
   in hcamsb , we take the ssb terms to be of the form : m_1 & = & _ 1+m_3/2,m_a & = & m_3/2 ,  a=2 ,  3  m_i^2 & = & -14\ { _ g+_f}m_3/2 ^ 2 a_f & = & m_3/2 , where @xmath22 , @xmath23 is the beta function for the corresponding superpotential coupling , and @xmath24 with @xmath25 the wave function renormalization constant . 
   the wino and gluino masses ( @xmath26 and @xmath27 ) receive a contribution from the bino mass at the two loop level . 
   thus , in pure hypercharge mediation , they are one loop suppressed compared to the scalar masses . 
   for convenience , we assume the above ssb mass parameters are input at the gut scale , and all weak scale ssb parameters are determined by renormalization group evolution .    we have included the above hcamsb model into the isasugra subprogram of the event generator isajet v7.79@xcite . after input of the above parameter set , 
   isasugra then implements an iterative procedure of solving the mssm rges for the 26 coupled renormalization group equations , taking the weak scale measured gauge couplings and third generation yukawa couplings as inputs , as well as the above - listed gut scale ssb terms . 
   isasugra implements full 2-loop rg running in the @xmath28 scheme , and minimizes the rg - improved 1-loop effective potential at an optimized scale choice @xmath29@xcite to determine the magnitude of @xmath21 and @xmath30 . 
   all physical sparticle masses are computed with complete 1-loop corrections , and 1-loop weak scale threshold corrections are implemented for the @xmath31 , @xmath32 and @xmath33 yukawa couplings@xcite . 
   the off - set of the weak scale boundary conditions due to threshold corrections ( which depend on the entire superparticle mass spectrum ) , necessitates an iterative up - down rg running solution . 
   the resulting superparticle mass spectrum is typically in close accord with other sparticle spectrum generators@xcite .    once the weak scale sparticle mass spectrum is known , then sparticle production cross sections and branching fractions may be computed , and collider events may be generated . 
   then , signatures for hcamsb at the cern lhc may be computed and compared against standard model ( sm ) backgrounds . 
   our goal in this paper is to characterize the hcamsb parameter space and sparticle mass spectrum , and derive consequences for the cern lhc @xmath34 collider , which is expected to begin operation in fall , 2009 . 
   some previous investigations of mamsb at lhc have been reported in ref . 
   @xcite . 
   the remainder of this paper is organized as follows . in sec . 
   [ sec : pspace ] , we calculate the allowed parameter space of hcamsb models , imposing various experimental and theoretical constraints . 
   we also show sample mass spectra from hcamsb models , and show their variation with @xmath2 and @xmath11 . 
   we show typical values of @xmath35 and @xmath36 that result . in sec . 
   [ sec : lhc ] , we explore consequences of the hcamsb model for lhc sparticle searches . 
   typically , collider events are characterized by production of high @xmath37 @xmath32 and @xmath31 quarks , along with @xmath38 and observable tracks from late decaying charginos @xmath39 . for small @xmath2 
   , slepton pair production may be visible , while for large @xmath2 , direct @xmath40 and @xmath41 production may be visible . 
   the lhc reach for 100 fb@xmath3 should extend up to @xmath42 ( 105 ) tev , corresponding to a reach in @xmath43 ( 2.2 ) tev , for small ( large ) values of @xmath2 . 
   the hcamsb model should be easily distinguishable from the mamsb model at the lhc if @xmath6 is not too large , due to the presence of @xmath44 candidates in cascade decay events . 
   the presence of these reflects the mass ordering @xmath0 in the hcamsb model , while @xmath45 in the mamsb model . in sec . 
   [ sec : conclude ] , we present our conclusions and outlook for hcamsb models . 
   we begin our discussion by plotting out in fig . [ 
   fig : m10 ] the mass spectra of various sparticles versus _ a _ ) . 
   @xmath46 in mamsb and _ b _ ) . 
   @xmath2 in the hcamsb model , for @xmath11 fixed at 50 tev , while taking @xmath47 , @xmath48 and @xmath49 gev . for @xmath13 and @xmath50 
   , the yellow - shaded region yields the well - known tachyonic slepton mass - squared values , which could lead to electric charge non - conservation in the scalar potential . in mamsb , as @xmath13 increases , all the scalars increase in mass , while @xmath51 , @xmath52 and @xmath53 remain roughly constant , and the superpotential @xmath21 term decreases . 
   the large @xmath13 limit of parameter space is reached around @xmath54 , where ewsb is no longer properly broken ( signaled by @xmath55 ) . 
   we also see the well - known property of mamsb models that @xmath56 . 
   in addition , an important distinction between the two models is the mass ordering which enters into the neutralino mass matrix : we find typically that @xmath0 in the hcamsb model , while @xmath1 in mamsb . thus , both models will have a wino - like @xmath57 state . 
   however , in the hcamsb model , the @xmath58 are dominantly higgsino - like states , with @xmath59 being bino - like , while in the mamsb model , we expect @xmath60 to be bino - like with @xmath61 being higgsino - like . 
   this mass ordering difference will give rise to a crucial distinction in lhc susy cascade decay events ( see sec . 
   [ sec : lhc ] ) which may serve to distinguish the two models .    in the hcamsb case , as @xmath2 increases , the gut scale gaugino mass @xmath16 increases . 
   thus , the bino mass increases with @xmath2 , while the light charginos @xmath39 and neutralino @xmath57 remain wino - like with mass fixed near @xmath26 , and the gluino remains with mass fixed at nearly @xmath62 . 
   many of the scalar masses also vary with @xmath2 . 
   the reason is that as @xmath2 increases , so does the gut scale value of @xmath16 . 
   the large value of @xmath16 feeds into the scalar masses via their renormalization group equations , causing many of them to increase with @xmath2 , with the largest increases occurring for the scalars with the largest weak hypercharge assignments @xmath63 . 
   thus , we see strong increases in the @xmath64 , @xmath65 and especially the @xmath66 masses with increasing @xmath67 . 
   the @xmath68 squark only receives a small increase in mass , since its hypercharge value is quite small : @xmath69 . from fig . 
   [ fig : m10]_b _ ) . 
   , we already see an important distinction between mamsb and hcamsb models : in the former case , the @xmath65 and @xmath66 states are nearly mass degenerate , while in the latter case these states are highly split , with @xmath70 . 
   an exception to the mass increase with @xmath2 in fig . 
   [ fig : m10]_b _ ) . occurs in the values of @xmath71 and @xmath72 . in these cases , 
   the large increase in @xmath73 feeds into the rge @xmath74 term@xcite , and _ amplifies _ the top - quark yukawa coupling suppression of the @xmath75 term . 
   since the doublet @xmath76 contains both the @xmath77 and @xmath78 states , both of these actually suffer a _ decrease _ in mass with increasing @xmath2 . 
   thus , we expect in hcamsb models with moderate to large @xmath2 that the third generation squark states will be highly split . for large @xmath67 
   , we expect the light third generation squarks @xmath79 and @xmath80 to be quite light , with a dominantly left- squark composition 
   . the heavier squarks @xmath81 and @xmath82 will be quite heavy , and dominantly right - squark states . 
   in addition , we see from fig . [ fig : m10]_b _ ) . that the superpotential @xmath21 term _ decreases _ with increasing @xmath2 . 
   at moderate - to - large @xmath6 , the @xmath21 term is from the tree - level scalar potential minimization conditions @xmath83 . 
   the running of @xmath84 versus energy scale @xmath85 is shown in fig . 
   [ fig : mhu ] for @xmath86 and 0.195 . 
   we see that as @xmath2 increases , the value of @xmath87 actually decreases , leading to a small @xmath88 value . 
   the relevant rge reads = ( - g_1 ^ 2m_1 ^ 2 -3g_2 ^ 2m_2 ^ 2 + g_1 ^ 2 s+3f_t^2 x_t ) . 
   a large value of @xmath16 thus leads to an _ upwards _ push to @xmath84 in its early running from @xmath89 , which is only later compensated by the downward push of the yukawa - coupling term involving the top yukawa coupling @xmath90 . in the figure , for the case of @xmath91 , the weak scale value of @xmath84 is actually positive . upon adding the large 1-loop corrections to the effective potential ( due to the light top - squark ) , 
   the rg - improved scalar potential yields a positive value of @xmath88 . 
   thus , in the region of large @xmath2 , where @xmath21 becomes small and comparable to @xmath26 , we expect the neutralino @xmath57 to become a mixed wino - higgsino particle , and the corresponding @xmath92 mass gap to increase beyond the value @xmath93 mev which is expected in amsb models@xcite . 
   parameter as a function of energy scale @xmath85 for @xmath94 , @xmath95 and @xmath96 for @xmath97 tev and @xmath47 , @xmath48 in the hcamsb model . , 
   scaledwidth=50.0% ]    an interesting coincidence related to the rg evolution of @xmath84 in the limit where hypercharge mediation dominates is that the electroweak symmetry breaking _ requires _ the electroweak scale to be @xmath98 orders of magnitude below the scale @xmath99 ( @xmath99 may be of order the gut scale or string scale ) at which the bino mass @xmath16 is generated . 
   if the hierarchy between the electroweak scale and @xmath99 was smaller , then a susy breaking scenario in which hypercharge mediation dominates would not be capable of triggering ewsb ( the energy interval for rg evolution would not be large enough to drive the @xmath84 parameter to negative values ) . 
   this is a very uncommon feature among susy breaking scenarios .    for a more detailed comparison , 
   we list in table [ tab : cases ] the sparticle mass spectrum for a mamsb point with @xmath100 gev , @xmath97 tev , @xmath47 and @xmath48 , and two hcamsb points with small and large @xmath2 values equal to @xmath101 and @xmath96 . 
   while all three cases have a comparable gluino mass , we see that the rather small splitting amongst @xmath102 and also @xmath103 states in mamsb is turned to large left - right splitting in the hcamsb cases . 
   we also see that the @xmath104 mev mass gap in amsb and hcamsb1 which leads to long - lived and possibly observable @xmath105 tracks in collider detectors opens up to a few gev in the hcamsb2 case . 
   the latter mass gap is large enough to make the @xmath105 state less long lived , although still maintaining possibly measureable tracks in collider scattering events . 
   the value of @xmath106 versus @xmath2 is shown in fig . [ 
   fig : ctau ] , where we usually get @xmath107 mm for most @xmath2 values . 
   the value drops to shorter lengths for large @xmath2 . 
   the shorter travel time of the @xmath105 would distinguish the large @xmath2 hcamsb case with a mixed higgsino - wino @xmath57 state from the low @xmath2 hcamsb case where @xmath57 is instead nearly pure wino - like . 
   .masses and parameters in  gev units for three case study points amsb , hcamsb1 and hcamsb2 using isajet 7.79 with @xmath49 gev and @xmath48 . 
   we also list the total tree level sparticle production cross section in fb at the lhc . [ cols="<,^,^,^",options="header " , ] 
   in this paper , we have examined some phenomenological consequences of hypercharged anomaly - mediated susy breaking models at the lhc . 
   we have computed the expected sparticle mass spectrum , and mapped out the relevant parameter space of the hcamsb model . 
   we have computed sparticle branching fractions , production cross sections and expected lhc collider events , and compared against expectations for sm backgrounds . 
   our main result was to compute the reach of the lhc for hcamsb models assuming 100 fb@xmath3 of integrated luminosity . 
   we find an lhc reach to @xmath42 tev ( corresponding to @xmath43 tev ) for low values of @xmath2 , and a reach to @xmath108 tev ( corresponding to @xmath109 tev ) for large @xmath2 . 
   we expect the reach for @xmath110 to be similar to the reach for @xmath48 , due to similarities in the spectra for the two cases ( see fig . 
   [ fig : m10 ] . ) 
   we also expect the reach for large @xmath6 to be similar to the reach for low @xmath6 in the @xmath111 and @xmath112 channels ( differences in the multi - lepton channels can occur due to enhanced -ino decays to taus and @xmath32s at large @xmath6 ) . 
   the lhc reach for hcamsb models tends to be somewhat lower than the reach for mamsb models , where ref . 
   @xcite finds a 100 fb@xmath3 reach of @xmath113 tev for low values of @xmath13 . 
   this is due in part because , in mamsb , the various squark states are more clustered about a common mass scale @xmath13 , while in hcamsb the squark states are highly split , with @xmath114 . 
   the hcamsb lhc event characteristics suffer similarities and differences with generic mamsb models . 
   both hcamsb and mamsb give rise to multi - jet plus multi - lepton plus @xmath38 event topologies , and within these event classes , it is expected that occasional hits of length a few _ cm _ will be found , arising from production of the long - lived wino - like chargino states . 
   some of the major differences between the models include the following . 
   a severe left - right splitting of scalar masses is expected in hcamsb , while left - right scalar degeneracy tends to occur in mamsb . 
   this may be testable if some of the slepton states are accessible to lhc searches . 
   it is well known that in mamsb , @xmath56 , while in hcamsb , @xmath115 , since the @xmath66 state has a large weak hypercharge quantum number . 
   in addition , the lightest stau state , @xmath116 , is expected to be mainly a left- state in hcamsb , while it is mixed , but mainly a right- state in mamsb . while it is conceivable that the left - right mixing might be determined at lhc ( using branching fractions or tau energy distributions ) , 
   such measurements would be easily performed at a linear @xmath117 collider , especially using polarized beams@xcite .    in hcamsb models , 
   the light third generation squarks @xmath79 and @xmath80 are expected to be generically lighter than the gluino mass , and frequently much lighter . 
   this leads to cascade decays which produce large multiplicities of @xmath32 and @xmath31 quarks in the final state . 
   thus , in hcamsb models , a rather high multiplicity of @xmath32 jets is expected . in mamsb , 
   a much lower mutiplicity of @xmath32-jets is expected , although this depends also on the value of @xmath6 which is chosen .    in hcamsb models , 
   the @xmath14 gaugino mass @xmath16 is expected to be the largest of the gaugino masses , with a mass hierarchy of @xmath0 . 
   this usually implies that the @xmath59 neutralino is mainly bino - like , while @xmath60 and @xmath118 are higgsino - like , and @xmath57 is wino - like . 
   in contrast , in the mamsb model , usually the ordering is that @xmath1 , so that while @xmath57 is again wino - like , the @xmath60 state is bino - like , and @xmath118 and @xmath59 are higgsino - like . 
   the compositions of the @xmath119 for @xmath120 will not be easy to determine at lhc , but will be more easily determined at a linear @xmath117 collider . 
   however , the mass ordering gives rise to os dilepton distributions with a prominent @xmath121 peak in hcamsb , while such a peak should be largely absent in mamsb models ( except at large @xmath6 where there is greater mixing in the neutralino sector ) . 
   thus , cascade decay events containing hits along with a @xmath121 peak in the os dilepton invariant mass distribution may be a smoking gun signature for hcamsb models at the lhc , at least within the lower range of @xmath6 . 
   this work was supported in part by the u.s . 
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summary: we investigate the phenomenological consequences of string models wherein the mssm resides on a d - brane , and the hypercharge gaugino mass is generated in a geometrically separated hidden sector . 
   this hypercharged anomaly - mediated susy breaking ( hcamsb ) model naturally solves the tachyonic slepton mass problem endemic to pure amsb scenarios . in hcamsb , 
   one obtains a mass ordering @xmath0 with split left- and right- scalars , whereas in mamsb models , one obtains @xmath1 with nearly degenerate left- and right- scalars . 
   we compute the allowed parameter space and expected superparticle mass spectrum in the hcamsb model . for low values of the hc and amsb mixing parameter @xmath2 , 
   the spectra is characterized by light left - sleptons , while the spectra for large @xmath2 is characterized by light top- and bottom- squarks . 
   we map out the approximate reach of lhc for hcamsb , and find that with 100 fb@xmath3 of integrated luminosity , a gravitino mass of @xmath4 ( 105 ) tev can be probed for low ( high ) values of @xmath2 , corresponding to a gluino mass reach of @xmath5 ( 2.2 ) tev . both cases 
   contain as is typical in amsb models long lived charginos that should yield visible highly ionizing tracks in the lhc detector . also , in the lower @xmath6 range , hcamsb models give rise to reconstructable @xmath7 candidates in susy cascade decay events , while mamsb models should do so only rarely . 
   * prospects for hypercharged anomaly mediated + susy breaking at the lhc *   +    howard baer@xmath8 , radovan derm ' iek@xmath9 , shibi rajagopalan@xmath10 , heaya summy@xmath10 +     _ 1 . dept . of physics and astronomy , university of oklahoma , norman 
   , ok 73019 , usa + 2 . 
   dept . of physics , indiana university , bloomington in 47405 , usa 
   + _