Ryuichiro Kitano- Non-thermal Gravitino Dark Matter

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    Non-thermal Gravitino Dark Matter

    Ryuichiro Kitano (LANL)

    [email protected], U. of New Mexico, May 19-23, 2008

    (based on PRD75,055003,2007 [hep-ph/0611111] with M.Ibe)

    LA-UR-08-03549

    mailto:[email protected]:[email protected]
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    Contents

    * SUSY dark matter

    * Moduli/gravitino problem

    * Gravitino dark matter

    * Summary

    * WIMP neutralino scenario

    * Is neutralino dark matter natural?

    * Conditions to be satisfied

    * Are these consistent with the neutralino dark matter scenario?

    * General framework of SUSY models

    * Dark matter abundance

    * Property of gravitino dark matter (Is it cold?)

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    SUSY dark matter

    Neutralino dark matter

    What is neutralino? -- Gauge singlet fermions in the MSSM

    * Bino U(1)Y gaugino

    * neutral Wino One of SU(2)L gauginos

    * neutral Higgsinos

    They mix each other by EWSB.

    If the lightest one is the lightest SUSY particle --> Stable

    --> Candidate for dark matter

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    The Standard mechanism of the Dark Matter generation

    Thermal decoupling

    Boltzmann eq.

    unimportant after decoupleunimportant after freeze out

    (number density at the timeof freezing out)

    great!!!

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    Assumptions made in this scenario:

    1. Neutralino is the LSP (stable)

    2. The universe is radiation dominated at the time of decoupling.3. No entropy production below T

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    Moduli/Gravitino Problem

    In the gravity mediation scenario, there is always a singlet scalar fieldwhich obtain a mass mainly through the SUSY breaking.

    This is non-zero.

    This field must be singlet, andcannot be stabilized in a super-symmetric way otherwise itcannot carry the SUSY breaking

    vev.

    Therefore, there exists a modulus field.

    We need to include this field to consider the cosmological history.

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    Moduli cosmology

    S is singlet Moduli problem

    During inflation,S potential is deformed

    Large initial amplitude

    [Coughlan, Fischler, Kolb, Raby, Ross '83]

    [Banks, Kaplan, Nelson '93]

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    Once S-domination happens, it's a cosmological disaster.

    decay always has O(1) branching ratio (if open)

    ... It's terrible.

    If the gravitino is a stable particle (LSP), it is toomuch abundance. We need more radiation!

    If it is not the lightest, the gravitinos decay at ~O(year).

    This destroys the standard BBN.

    Gravitino is a major energy density component.

    In gravity mediation,

    because S couples to other fields only with 1/MPl suppressedoperators.

    If the decay is kinematically forbidden, it means S has a lifetime ofO(year).

    It's clearly inconsistent with the neutralino dark matter scenario.

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    For the standard neutralino dark matter scenario to work, we need one ofthe following:

    * some special inflation model that does not couple to the S field.

    * a very low scale inflation such that the deformation of the S potentialis small enough.

    * a lucky enough initial condition such that S domination doesn't happen.

    Wmm... It may be the case but I don't like it.

    Is there a good cosmological scenario that does not require such conditions?

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    Are there consistent SUSY cosmology with such a scalar field?

    Let's first fix the framework.

    SUSY breaking

    V=m4

    Effective Lagrangian:

    m /4 2

    Gauge Mediation

    MSSMSUSY

    Yes, gauge mediation offers an interesting possibility ofnon-thermal gravitino dark matter

    messengerCharged under the SMgauge group.

    In this framework, the gravitinois the LSP.

    [RK '06]

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    During inflation,S potential is deformed

    Large initial amplitude

    Gravitino production!

    This I called 'moduli/gravitino problem,' but now it's a mechanism

    for the dark matter production.

    Non-thermal Gravitino dark matter [Ibe, RK '06]

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    Non-thermal gravitino production

    Step 1: After inflation, S oscillation starts

    Step 2: S decays and reheat the Universe

    Step 3: gravitino cooling

    Let's discuss it step by step.

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    Step 1: oscillation

    perturbative correction supergravity effect (tadpole)

    Logarithmic potential

    quadratic potential

    SUSY breaking vacuum is supported by |S|^2, but SUSY vacuumis just log.

    SUSY breaking vacuum is more attractive at most point onthe complex S plane!

    S-potential

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    If initial value of S is not at =0, S rolls down to the SUSYbreaking vacuum when H~mS.

    We are attractive!!

    St 2 S d Interaction Lagrangian of S

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    Step 2: S decay Interaction Lagrangian of S

    * S gauge boson coupling

    with

    * S gaugino coupling

    with

    * S scalar couplingSimilarly togauginos

    We can read off from the S dependenceof low energy parameters.

    S-to-superparticle couplings are proportional to their masses.

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    Point

    1. interactions are suppressed by 1/.

    Shorter lifetime compared to the gravity mediation case.

    Good for BBN!

    * S gravitino coupling

    Fermionic component of S goldstino gravitino

    2. gravitino coupling is supressed by m3/2!

    Smaller branching ratio of

    Good for the gravitino abundance!

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    Lifetime and gravitino abundance

    What's the main decay channel?

    Actually, must be forbiddenBBN

    In gauge mediation, or is the NLSP.

    is the dominant decay mode if it's open.

    BBN OKGravitino abundance

    Perfect for Dark Matter!!

    Decay temperature

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    Correct dark matterabundance forO(1GeV) gravitinos!

    i i li

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    Step 3: gravitino cooling

    Are gravitinos cold?

    Well, they are non-thermally produced.

    Their distribution is not the thermal one.

    at the time of production, but it slows down by redshift.

    Anyway, they must be non-relativistic at the time of the structureformation.

    In this scenario,

    It's OK.

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    In terms of

    It's interesting that coincides with the Grand Unification scale!

    In fact, O(1) GeV gravitino is also motivated by the -problem!

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    Sweet Spot Supersymmetry[Ibe, RK '07]

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    Summary

    * When we think of SUSY cosmology, we should be careful of

    consistency with the underlying model. Especially, the scalarpartner of the goldstino and the gravitino are dangerous.

    * The gauge mediation model provides viable cosmology with

    non-thermally produced gravitino dark matter.

    * Baryogenesis, inflation model building etc. in this scenario areinteresting to do. There may be some non-trivial predictions...