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Z’ Mediation of Supersymmetry Breaking. Itay Yavin Princeton University. arXiv:0710.1632 [hep-ph] - G. Paz, P. Langacker, L. Wang and IY arXiv:0801.3693 [hep-ph] - G. Paz, P. Langacker, L. Wang and IY arXiv:0711.3214 [hep-th] - H. Verlinde , L. Wang, M. Wijnholt and IY. Outline. Motivation

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Z mediation of supersymmetry breaking

Z’ Mediation of Supersymmetry Breaking

Itay Yavin

Princeton University

arXiv:0710.1632 [hep-ph]- G. Paz, P. Langacker, L. Wang and IY

arXiv:0801.3693 [hep-ph]- G. Paz, P. Langacker, L. Wang and IY

arXiv:0711.3214 [hep-th]- H. Verlinde , L. Wang, M. Wijnholt and IY



  • Motivation

  • Connection with String theory

  • A model

    • Setup

    • Experimental signatures

  • Extensions


The forces of nature


The Forces of Nature

Electromagnetic force

Strong force

Atoms ~ 10-10 m

Weak force

Protons and Neutrons

~ 10-15 m

Radioactive decay

~ 10-18 m

Why is the weak force stronger than gravity?

Are there any other forces?


A fifth force an extra abelian gauge boson
A Fifth Force (an extra Abelian gauge-boson)

Supersymmetry (an extended spacetime sym.)

  • There are many reasons to conjecture that supersymmetry exists in nature,

    • Consistent theories of quantum gravity predict its existence.

    • Grand unified theories work better with it.

    • Helps to explain, both statically and dynamically why the Weak force is stronger than the gravitational force.

  • There are many reasons to conjecture that a fifth force exists in nature,

    • Consistent theories of quantum gravity almost always include it.

    • Grand unified theories have it.

    • Certain unexplained global symmetries of the Standard Model seem to demand it.


Supersymmetry breaking

No D-terms

Supersymmetry Breaking

None of the degrees of freedom associated with these symmetries are seen at low energies. Following the paradigm of SUSY breaking in a hidden sector (see H. P. Nilles talk) we propose the following scenario

U’(1) and EWSB is dynamically generated.


Z mediation in string theory
Z’ mediation in String theory

An abelian gauge field can mix with the RR-form in the gravitational multiplet. The RR-form propagates in the bulk and can act to mix two U(1)’s on remote branes.


Charge assignment and anomaly cancellation conditions
Charge assignment and anomaly cancellation conditions

Assume that only matter on the visible brane participate in the anomaly cancellation conditions.

Also, allow for the following coupling of the singlet field,

D, Dc are colored exotics.

E, Ec are color singlet exotics.

Solving for the anomaly cancellation conditions:

Two free charges Q2 and QQand nD = 3, nE = 2.


General features and fine tuning
General features and fine-tuning

The gauginos are not charged under the new force and don’t directly interact with it. Nonetheless, they feel it quantum mechanically,

The scalars are at roughly 100 TeV and so fine-tuning is inevitable. This is a mini-version of the split SUSY scenario,

N. Arkani-Hamed, S.~Dimopoulos, hep-th/0405159

G. Giudice and A. Romanino, hep-ph/0406088






The singlet must break the U’(1) gauge-symmetry in the visible sector, generate a term, and give the exotics a mass.


(positive contribution)

(negative contribution)

Singlet’s U’(1) charge cannot be too large.

Yukawa coupling to exotics cannot be too small


mS sets the masses of the Z’ gauge-boson and the singlino’s


 varyingS we can fine-tune one against the other

The two Higgs doublet mass matrix is,

Note: This tuning leads to some amount of accidental tuning:


Energy scales






Matter scalar partners


Energy Scales

Supersymmetry is broken. Only the Z’ vector supermultiplet feels the breaking directly.


Electroweak scale





Electroweak Scale

Electroweak scale


Scanning over parameter space charge assignment
Scanning over parameter space(charge assignment)

The red dots represent charge assignment for which a viable solution for the Electroweak scale. The Yukawa were chosen to be,

= yD = 0.5 yE = 0.1


Scanning over parameter space exotic yukawa couplings
Scanning over parameter space (Exotic Yukawa couplings)

Z’ gauge-boson





Discovery @ lhc
Discovery @ LHC

Proton - Proton Collider at 14 TeV

Proton - Proton Collider at 10 TeV


Higgs mass
Higgs Mass

The physical Higgs mass is determined by the quartic,

But, the quartic is determined by the boundary condition and the RGE, which don’t change appreciably in the model we consider,

So the Higgs mass is almost entirely determined by the running from 1000 TeV down to the Electroweak scale,


Exotic gluino decay
Exotic Gluino Decay

Since all the scalar partners are heavy, the gluino must decay through an off-shell intermediate scalar,

We may never be able to resolve the intermediate particle, but we may observe the long life-time of the gluino!


Exotic gluino decay continued
Exotic Gluino Decay - Continued…

The parametric dependence of the two processes is very different.

Gambino, Giudice and Slavich arXiv:hep-ph/0506214

Arvanitaki et al arXiv:hep-ph/0506242.

Life-time for different benchmark points.

Similar calculations in the context of split susy were done by Toharia and Wells arXiv:hep-ph/0503175


Glueballino and other exotic hadrons










Glueballino and other exotic Hadrons

The gluino is long lived, but not long enough to leave a displaced vertex. It will first hadronize and then decay,





Hadronic bound state.

Is there any way to experimentally distinguish between a gluon that decay before or after hadronizing?

Grossman and Nachshon - arXiv:0803.1787 [hep-ph]


Z production




Z’ Production

If a new force is indeed waiting to be discovered, then we may just observe its carrier directly at the LHC,

Too many refs. . .


Other signatures
Other Signatures

After its discovery it will be easier to explore the other decay modes of the heavy vector-boson.

The collider signatures have not been thoroughly investigated yet, hopefully in the near future . . .






  • Split-SUSY spectrum

  • Exotic gluino decay

  • Z’ production

  • Higgs mass at 140 GeV

  • Light singlino



Dark matter remains a problem in this type of scenario. When the wino is the LSP the density is too low. If either the singlino or gravitino are the LSP it is usually a disaster. Any way out?

Unification: not present in the current model. Work in progress. . . seems difficult (Axions).

In this setup we assumed UV boundary conditions analogues to gaugino-mediation. How do things change if we were to consider a gauge-mediation type setup?

Including more details of the hidden sector.

A more extensive study of realizations of such a setup in the context of string theory. But see: Grimm and Klemm arXiv; 0805.3361[hep-th].

Any connection with the landscape?






Our current best speculations about the UV almost always lead to the existence of additional U’(1) gauge fields at low energies. This may fit nicely as a (bulk) mediator of SUSY breaking.

The resulting model is dynamical, calculable and predictive.

3) The general features are quite robust and lead to distinct signatures. With some luck we’ll be able to see it at the LHC!!!


Beta decay
Beta decay

Radioactivity was observed before the discovery of the electron. We are still trying to uncover the nature of the weak force. It may be instructive to recall that it took about 30 years before scientists figured out what Beta decay was all about:

Experimental difficulties and confusion: “. . . The ignorance at the time about the relation between the blackening of a photographic plate and the intensity of the irradiation.”(Pais, Inward Bound)

Theoretical misunderstanding and prejudices: “ . . . Prevailing prejudice still strongly favoured a discrete spectrum possibly due to a monoenergetic primary source.”(Pais)

Real physics: discrete lines in the spectrum due to (the yet undiscovered) nuclear structure.


Fermi on the problem of the meson
Fermi on the problem of the meson:

“Of course, it may be that someone will come up soon with a solution to the problem of the meson, and that experimental results will confirm so many detailed features of the theory that it will be clear to everybody that it is the correct one. Such things have happened in the past. They may happen again. However, I do not believe that we can count on it, and I believe that we must be prepared for a long, hard pull.” (E. Fermi, Collected works, paper 247)


Gravitino mass
Gravitino mass

The gravitino mass is given as usual,

But, the SUSY breaking scale is very sensitive to the precise details of the model,

Hard to predict. Need more details about the hidden sector and the precise mechanism of SUSY breaking.


U 1 mixing
U(1) Mixing

Will be induced at loop level. Consider the superpotential,

By construction k does not have an F-term. It’s lowest component is roughly,

Which will induce kinetic mixing. However, since in the limit that M1 vanishes there is chiral symmetry protecting it so,