Mediated SUSY Breaking Research Articles

From the unification scale to the weak scale: A self consistent supersymmetric Dine-Fischler-Srednicki-Zhitnitsky axion model

The distinguishing feature of the Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion is that it couples to the electroweak Higgs fields. There is thus an immediate connection between the Peccei-Quinn (PQ) scale and the weak scale. We wish to incorporate the DFSZ axion in a complete supersymmetric model, valid at all scales, and then to implement it in a numerical code connecting the high scale and the low scale physics on a quantitative level. We find that the simplest supersymmetric DFSZ model, as proposed by Rajagopal et al. in 1990, is inconsistent when we consider the minimization of the scalar potential. The problem is that we obtain a negative squared mass for the saxion, the scalar partner of the axion, at the minimum. We then consider the minimal extension in order to get a consistent model for all scales: one has to include an additional explicit sector to spontaneously break the PQ symmetry. In the complete model we can determine the mass of the axino, the fermionic partner of the axion. It is useful to distinguish two cases: (1) the supersymmetry (SUSY) breaking scale is lower than the PQ breaking scale, and (2) the scales are comparable. We find that the axino is very light in (1), while its mass is generically of the order of the other soft SUSY breaking masses in (2). We have implemented SUSY breaking via generic soft breaking terms, and thus make no explicit statement about the form and mediation of SUSY breaking. This complete model can then be incorporated in a numerical code connecting the two scales. We briefly discuss the renormalization group equations and the couplings of the axion to gluons and photons.

SUSY models under siege: LHC constraints and electroweak fine-tuning

Recent null results from LHC8 SUSY searches along with the discovery of a SM-like Higgs boson with mass m(h) ~ 125.5 GeV indicates sparticle masses in the TeV range, causing tension with conventional measures of electroweak fine-tuning. We propose a simple Fine-tuning Rule which should be followed under any credible evaluation of fine-tuning. We believe that overestimates of electroweak fine-tuning by conventional measures all arise from violations of this rule. We show that to gain accord with the Fine-tuning Rule, then both Higgs mass and the traditional \Delta_{BG} fine-tuning measures reduce to the model-independent electroweak fine-tuning measure \Delta_{EW}. This occurs by combining dependent contributions to m(Z) or m(h) into independent units. Then, using \Delta_{EW}, we evaluate EW fine-tuning for a variety of SUSY models including mSUGRA, NUHM1, NUHM2, mGMSB, mAMSB, hyper-charged AMSB and nine cases of mixed moduli-anomaly (mirage) mediated SUSY breaking models (MMAMSB) whilst respecting LHC Higgs mass and B-decay constraints (we do not impose LHC8 sparticle mass constraints due to the possibility of compressed spectra within many of these models). We find mSUGRA, mGMSB, mAMSB and MMAMSB models all to be highly fine-tuned. The NUHM1 model is moderately fine-tuned while NUHM2 which allows for radiatively-driven naturalness (RNS) allows for fine-tuning at a meager 10% level in the case where m(higgsinos) ~ 100-200 GeV and the TeV-scale top squarks are well-mixed. Models with RNS may or may not be detect at LHC14. A \sqrt{s} ~ 500 GeV e^+e^- collider will be required to make a definitive search for the requisite light higgsinos.

Multiphoton signatures of goldstini at the LHC

We study models of gauge mediated SUSY breaking with more than one hidden sector. In these models the neutralino sector of the MSSM is supplemented with additional light neutral fermions, the nearly massless gravitino and the massive pseudo-goldstini. For the case where the Bino is the lightest ordinary SUSY particle, its preferred decay is to a photon and the heaviest pseudo-goldstino, which generically cascades down to lighter pseudo-goldstini, or to the gravitino, in association with photons. This gives rise to multiphoton plus missing energy signatures at the LHC. We investigate in detail simplified models where the SUSY spectrum consists of the right-handed sleptons, a Bino-like neutralino, the pseudo-goldstini and the gravitino. We compare against existing LHC searches and show that the sensitivity to our models could be significantly improved by relaxing the kinematic cuts and requiring additional final state particles. We propose inclusive searches in the final state with at least three photons plus missing energy and in the final state with at least two photons plus two leptons plus missing energy, the former being sensitive to any production mode and the latter being optimized for slepton pair production. We show that they could lead to an observation (or strong constraints) already with the data set from LHC Run I, and present prospects for LHC Run II.

Light third-generation squarks from flavour gauge messengers

We study models of gauge-mediated supersymmetry breaking with a gauged horizontal SU(3)_F symmetry acting on the quark superfields. If SU(3)_F is broken non-supersymmetrically by F-term vacuum expectation values, the massive gauge bosons and gauginos become messengers for SUSY breaking mediation. These gauge messenger fields induce a flavour-dependent, negative contribution to the soft masses of the squarks at one loop. In combination with the soft terms from standard gauge mediation, one obtains large and degenerate first- and second-generation squark masses, while the stops and sbottoms are light. We discuss the implications of this mechanism for the superparticle spectrum and for flavour precision observables. We also provide an explicit realization in a model with simultaneous SUSY and SU(3)_F breaking.

Nonuniversal supergravity at the LHC: Prospects and discovery potential

We explore supersymmetry (SUSY) parameter space with nonuniversal high scale parameters in a gravity mediated SUSY breaking (SUGRA) scenario that accommodates a Higgs mass of $(125\ifmmode\pm\else\textpm\fi{}2)\text{ }\text{ }\mathrm{GeV}$ while satisfying cold dark matter relic density and other low energy constraints. We indicate a few benchmark points consistent with different dark matter annihilation processes where third family squarks are lighter than the first two as a requirement to keep the Higgs mass within the limit. We show that bottom rich and leptonic final states have a better reach in such parameter space points and is the most likely scenario to discover SUSY at the upcoming run of LHC with center-of-mass energy 14 TeV.

Formula omitted] mediation for the natural SUSY and the anomalous muon [formula omitted

We propose a U(1)′ mediated supersymmetry (SUSY) breaking, in which U(1)′ is identified with U(1)B1+B2−2L1. The U(1)B1+B2−2L1 gauge symmetry, which is anomaly-free with the field contents of the minimal supersymmetric standard model, assigns ±1/3 charges to the first and second generations of the quarks, and ∓2 to the first generation of the leptons. As a result, the first two generations of squarks acquire masses of about 7 TeV, and the first generation of the sleptons do those of 40 TeV, respectively, in the presence of one or three pairs of extra vector-like matter {5,5¯}. Non-observation on extra colored particles below 1 TeV at the large hadron collider, and also the flavor violations such as μ−→e−γ are explained. By virtue of such a gauge symmetry, proton stability can be protected. The other squarks and sleptons as well as the gauginos can obtain masses of order 102−3 GeV through the conventional gravity or gauge mediated SUSY breaking mechanism. The relative light smuon/sneutrino and the neutralino/chargino could be responsible for the (g−2)μ deviated from the standard model prediction. The stop mass of ∼500 GeV relieves the fine-tuning problem in the Higgs sector. Two-loop effects by the relatively heavy sfermions can protect the smallness of the stop mass from the radiative correction by the heavy gluino (≳1 TeV). Extra vector-like matter can enhance the radiative corrections to the Higgs mass up to 126 GeV, and induce the desired mixing among the chiral fermions after U(1)B1+B2−2L1 breaking.

Implication of a Higgs boson at 125 GeV within the stochastic superspace framework

We revisit the issue of considering stochasticity of Grassmannian coordinates in $N=1$ superspace, which was analyzed previously by Kobakhidze et al. In this stochastic supersymmetry (SUSY) framework, the soft SUSY breaking terms of the minimal supersymmetric Standard Model (MSSM) such as the bilinear Higgs mixing, trilinear coupling, as well as the gaugino mass parameters are all proportional to a single mass parameter $\ensuremath{\xi}$, a measure of supersymmetry breaking arising out of stochasticity. While a nonvanishing trilinear coupling at the high scale is a natural outcome of the framework, a favorable signature for obtaining the lighter Higgs boson mass ${m}_{h}$ at 125 GeV, the model produces tachyonic sleptons or staus turning to be too light. The previous analyses took $\ensuremath{\Lambda}$, the scale at which input parameters are given, to be larger than the gauge coupling unification scale ${M}_{G}$ in order to generate acceptable scalar masses radiatively at the electroweak scale. Still, this was inadequate for obtaining ${m}_{h}$ at 125 GeV. We find that Higgs at 125 GeV is highly achievable, provided we are ready to accommodate a nonvanishing scalar mass soft SUSY breaking term similar to what is done in minimal anomaly mediated SUSY breaking (AMSB) in contrast to a pure AMSB setup. Thus, the model can easily accommodate Higgs data, LHC limits of squark masses, WMAP data for dark matter relic density, flavor physics constraints, and XENON100 data. In contrast to the previous analyses, we consider $\ensuremath{\Lambda}={M}_{G}$, thus avoiding any ambiguities of a post-grand unified theory physics. The idea of stochastic superspace can easily be generalized to various scenarios beyond the MSSM.

Enhanced Higgs mass in a gaugino mediation model without the Polonyi problem

We consider a SUSY breaking scenario without the Polonyi problem. To solve the problem, the enhanced couplings of the Polonyi field to an inflaton, gauge kinetic functions and itself are assumed. As a result, a gaugino mediated SUSY breaking occurs. In this scenario, the Higgs boson mass becomes consistent with the recently observed value of the Higgs-like boson (i.e., mh≃125 GeV) for the gluino mass about 4 TeV, which is, however, out of the reach of the LHC experiment. We show that the trilinear coupling of the scalar top is automatically enhanced by the presence of the extra matters. With such extra matters, the Higgs mass as large as 125 GeV can be realized with the gluino mass of 1–2 TeV which is within the reach of the LHC experiment. In our scenario, the gravitino is the lightest SUSY particle and the candidate for dark matter, and the Wino, Bino, and sleptons are in the range from 200 GeV to 700 GeV.

Anatomy of maximal stop mixing in the MSSM

Abstract A Standard Model-like Higgs near 125 GeV in the MSSM requires multi-TeV stop masses, or a near-maximal contribution to its mass from stop mixing. We investigate the maximal mixing scenario, and in particular its prospects for being realized it in potentially realistic GUT models. We work out constraints on the possible GUT-scale soft terms, which we compare with what can be obtained from some well-known mechanisms of SUSY breaking mediation. Finally, we analyze two promising scenarios in detail, namely gaugino mediation and gravity mediation with non-universal Higgs masses.

The messenger sector of SUSY flavour models and radiative breaking of flavour universality

Abstract The flavour messenger sectors and their impact on the soft SUSY breaking terms are investigated in SUSY flavour models. In the case when the flavour scale M is below the SUSY breaking mediation scale M S , the universality of soft terms, even if assumed at M S , is radiatively broken. We estimate this effect in a broad class of models. In the CKM basis that effect gives flavour off-diagonal soft masses comparable to the tree-level estimate based on the flavour symmetry.

Higgs mass and muon anomalous magnetic moment in supersymmetric models with vectorlike matters

We study the muon anomalous magnetic moment (muon g-2) and the Higgs boson mass in a simple extension of the minimal supersymmetric (SUSY) Standard Model with extra vector-like matters, in the frameworks of gauge mediated SUSY breaking (GMSB) models and gravity mediation (mSUGRA) models. It is shown that the deviation of the muon g-2 and a relatively heavy Higgs boson can be simultaneously explained in large tan-beta region. (i) In GMSB models, the Higgs mass can be more than 135 GeV (130 GeV) in the region where muon g-2 is consistent with the experimental value at the 2 sigma (1 sigma) level, while maintaining the perturbative coupling unification. (ii) In the case of mSUGRA models with universal soft masses, the Higgs mass can be as large as about 130 GeV when muon g-2 is consistent with the experimental value at the 2 sigma level. In both cases, the Higgs mass can be above 140 GeV if the g-2 constraint is not imposed.

SOFT LEPTOGENESIS AND GRAVITINO DARK MATTER IN GAUGE MEDIATION

In gauge mediated SUSY breaking models, the gravitino is generally the lightest SUSY particle and can be a candidate for a dark matter. However the viable abundance of the gravitino requires rather low reheating temparature. With this low reheating temparature, it is difficult to explain the baryon asymmetry of the universe with thermal leptogenesis. We consider the extended scenario of the gauge mediation, which generates A-terms. In this extended scenario, soft leptogenesis works successfully with the low reheating temperature. Therefore we can explain the baryon asymmetry and gravitino dark matter simultaneously.

Condensate cosmology in O’Raifeartaigh models

Flat directions charged under an R-symmetry are a generic feature of O'Raifeartaigh models. Non-topological solitons associated with this symmetry, R-balls, are likely to form through the fragmentation of a condensate, itself created by soft terms induced during inflation. In gravity mediated SUSY breaking R-balls decay to gravitinos, reheating the universe. For gauge mediation R-balls can provide a good dark matter candidate. Alternatively they can decay, either reheating or cooling the universe. Conserved R-symmetry permits decay to gravitinos or gauginos, whereas spontaneously broken R-symmetry results in decay to visible sector gauge bosons.

GAUGE MEDIATION OF SUPERSYMMETRY BREAKING AND THE FROGGATT–NIELSEN MECHANISM

In the model of gauge mediation of SUSY breaking in the presence of tree-level mediation, the Froggatt–Nielsen mechanism provides a different hierarchy of sparticle masses. We study the spectra and show the results to be like those in an effective supersymmetric model.

Anomaly mediated SUSY breaking scenarios in the light of cosmology and in the dark (matter)

Anomaly mediation is a popular and well motivated supersymmetry breaking scenario. Different possible detailed realisations of this set-up are studied and actively searched for at colliders. Apart from limits coming from flavour, low energy physics and direct collider searches, these models are usually constrained by the requirement of reproducing the observations on dark matter density in the universe. We reanalyse these bounds and in particular we focus on the dark matter bounds both considering the standard cosmological model and alternative cosmological scenarios. These scenarios do not change the observable cosmology but relic dark matter density bounds strongly depend on them. We consider few benchmark points excluded by standard cosmology dark matter bounds and suggest that loosening the dark matter constraints is necessary in order to avoid a too strong (cosmological) model dependence in the limits that are obtained for these models. We also discuss briefly the implications for phenomenology and in particular at the Large Hadron Collider.

Dark matter,μproblem, and neutrino mass with gaugedRsymmetry

We show that the mu problem and the strong CP problem can be resolved in the context of the gauged U(1)_R symmetry, realizing an automatic Peccei-Quinn symmetry. In this scheme, right-handed neutrinos can be introduced to explain small Majorana or Dirac neutrino mass. The U(1)_R D-term mediated SUSY breaking, called the U(1)_R mediation, gives rise to a specific form of the flavor-conserving superpartner masses. For the given solution to the mu problem, electroweak symmetry breaking condition requires the superpartners of the Standard Model at low energy to be much heavier than the gravitino. Thus dark matter candidate can be either gravitino or right-handed sneutrino. In the Majorana neutrino case, only gravitino is a natural dark matter candidate. On the other hand, in the Dirac neutrino case, the right-handed sneutrino can be also a dark matter candidate as it gets mass only from SUSY breaking. We discuss the non-thermal production of our dark matter candidates from the late decay of stau and find that the constraints from the Big Bang Nucleosynthesis can be evaded for a TeV-scale stau mass.

HOLOGRAPHIC SPACE–TIME AND ITS PHENOMENOLOGICAL IMPLICATIONS

I briefly review the theory of holographic space–time and its relation to the cosmological constant problem, and the breaking of supersymmetry (SUSY). When combined with some simple phenomenological requirements, these ideas lead to a fairly unique model for Tera-scale physics, which implies direct gauge mediation of SUSY breaking and a model for dark matter as a hidden sector baryon, with nonzero magnetic dipole moment.

Beyond the standard seesaw: neutrino masses from Kähler operators and broken supersymmetry

We investigate supersymmetric scenarios in which neutrino masses are generated by effective d=6 operators in the Kahler potential, rather than by the standard d=5 superpotential operator. First, we discuss some general features of such effective operators, also including SUSY-breaking insertions, and compute the relevant renormalization group equations. Contributions to neutrino masses arise at low energy both at the tree level and through finite threshold corrections. In the second part we present simple explicit realizations in which those Kahler operators arise by integrating out heavy SU(2)_W triplets, as in the type II seesaw. Distinct scenarios emerge, depending on the mechanism and the scale of SUSY-breaking mediation. In particular, we propose an appealing and economical picture in which the heavy seesaw mediators are also messengers of SUSY breaking. In this case, strong correlations exist among neutrino parameters, sparticle and Higgs masses, as well as lepton flavour violating processes. Hence, this scenario can be tested at high-energy colliders, such as the LHC, and at lower energy experiments that measure neutrino parameters or search for rare lepton decays.

SUPERNATURAL A-TERM INFLATION

Following Ref. 10, we explore the parameter space of the case when the supersymmetry (SUSY) breaking scale is lower, for example, in gauge mediated SUSY breaking model. During inflation, the form of the potential is V0 plus MSSM (or A-term ) inflation. We show that the model works for a wide range of the potential V0 with the soft SUSY breaking mass m ~ O(1) TeV. The implication to MSSM (or A-term) inflation is that the flat directions which is lifted by the non-renormalizable terms described by the superpotential [Formula: see text] with p = 4 and p = 5 are also suitable to be an inflaton field for λp = O(1) provided there is an additional false vacuum term V0 with appropriate magnitude. The flat directions correspond to p = 6 also works for [Formula: see text].

Gaugino anomaly mediated SUSY breaking: phenomenology and prospects for the LHC

We examine the supersymmetry phenomenology of a novel scenario of supersymmetry (SUSY) breaking which we call Gaugino Anomaly Mediation, or inoAMSB. This is suggested by recent work on the phenomenology of flux compactified type IIB string theory. The essential features of this scenario are that the gaugino masses are of the anomaly-mediated SUSY breaking (AMSB) form, while scalar and trilinear soft SUSY breaking terms are highly suppressed. Renormalization group effects yield an allowable sparticle mass spectrum, while at the same time avoiding charged LSPs; the latter are common in models with negligible soft scalar masses, such as no-scale or gaugino mediation models. Since scalar and trilinear soft terms are highly suppressed, the SUSY induced flavor and CP-violating processes are also suppressed. The lightest SUSY particle is the neutral wino, while the heaviest is the gluino. In this model, there should be a strong multi-jet +etmiss signal from squark pair production at the LHC. We find a 100 fb^{-1} reach of LHC out to m_{3/2}\sim 118 TeV, corresponding to a gluino mass of \sim 2.6 TeV. A double mass edge from the opposite-sign/same flavor dilepton invariant mass distribution should be visible at LHC; this, along with the presence of short-- but visible-- highly ionizing tracks from quasi-stable charginos, should provide a smoking gun signature for inoAMSB.