arXiv:hep-ph/0410178v1 12 Oct 2004
SuperWIMP Cosmology and Collider Physicsa
JONATHAN L. FENG∗, ARVIND RAJARAMAN∗, BRYAN T. SMITH∗,
SHUFANG SU†, FUMIHIRO TAKAYAMA∗
∗Department of Physics and Astronomy, University of California
Irvine, CA 92697, USA
†Department of Physics, University of Arizona
Tucson, AZ 85721, USA
Dark matter may be composed of superWIMPs, superweakly-interacting mas-
sive particles produced in the late decays of other particles. We focus here on
the well-motivated supersymmetric example of gravitino LSPs. Gravitino su-
perWIMPs share several virtues with the well-known case of neutralino dark
matter: they are present in the same supersymmetric frameworks (supergravity
with R-parity conservation) and naturally have the desired relic density. In con-
trast to neutralinos, however, gravitino superWIMPs are impossible to detect by
conventional dark matter searches, may explain an existing discrepancy in Big
Bang nucleosynthesis, predict observable distortions in the cosmic microwave
background, and imply spectacular signals at future particle colliders.
In recent years, there has been tremendous progress in understanding the universe on
the largest scales. In particular, the energy density in non-baryonic dark matter is known
to be 
ΩDM= 0.23 ± 0.04
in units of the critical density. At the same time, we have no idea what the microscopic
identity of non-baryonic dark matter is. The dark matter problem therefore provides
precise, unambiguous evidence for new physics and has motivated new particles such
as axions [2,3,4], neutralinos [5,6], Q balls , wimpzillas , axinos , self-interacting
dark matter , annihilating dark matter , Kaluza-Klein dark matter [12,13], bra-
nons [14,15], and many others.
Here we review a new class of dark matter candidates: superWIMPs, superweakly-
interacting massive particles produced in the late decays of other particles [16,17,18].
SuperWIMPs have several strong motivations:
• They are present in well-motivated frameworks for new physics, including models
with supersymmetry (supergravity with R-parity conservation) and extra dimen-
sions (universal extra dimensions with KK-parity conservation).
• Their relic density is naturally in the right range to be dark matter without the
need to introduce and fine-tune new energy scales.
aPlenary talk given by JLF at SUSY2004, the 12th International Conference on Supersymmetry and
Unification of Fundamental Interactions, Tsukuba, Japan, 17-23 June 2004.
• They can explain an existing anomaly, namely the observed underabundance of7Li
relative to the prediction of standard Big Bang nucleosynthesis.
• They have rich implications for early universe cosmology and imply spectacular
signals at the Large Hadron Collider (LHC) and the International Linear Collider
2. The Basic Idea
As noted above, superWIMPs exist in theories with supersymmetry and in models
with extra dimensions. We concentrate on the supersymmetric scenarios here. Details of
the extra dimensional realizations may be found in Refs. [16,17,18].
In the simplest supersymmetric models, supersymmetry is transmitted to standard
model superpartners through gravitational interactions, and supersymmetry is broken at
a high scale. The mass of the gravitino˜G is
and the masses of standard model superpartners are
˜ m ∼
where M∗ = (8πGN)−1/2≃ 2.4 × 1018GeV is the reduced Planck scale and F ∼
(1011GeV)2is the supersymmetry breaking scale squared. The precise ordering of masses
depends on unknown, presumably O(1), constants in Eq. (3). Most supergravity studies
assume that the lightest supersymmetric particle (LSP) is a standard model superpartner,
such as the neutralino. In this case, it is well-known that the neutralino naturally freezes
out with a relic density that is in the right range to account for dark matter .
The gravitino may be the LSP, however [16,17,18,20,21,22,23,24,25,26,27,28]. In su-
pergravity, the gravitino has weak scale mass Mweak∼ 100 GeV and couplings suppressed
by M∗. The gravitino’s extremely weak interactions imply that it is irrelevant during ther-
mal freeze out. The next-to-lightest supersymmetric particle (NLSP) therefore freezes out
as usual, and if the NLSP is a slepton, sneutrino, or neutralino, its thermal relic density is
again ΩNLSP∼ 0.1. However, eventually the NLSP decays to its standard model partner
and the gravitino. The resulting gravitino relic density is
In supergravity, where m˜G∼ mNLSP, the gravitino therefore inherits a relic density of the
right order to be much or all of non-baryonic dark matter. The superWIMP gravitino
scenario preserves the prime virtue of WIMPs, namely that they give the desired amount
 G. Servant and T. M. P. Tait, Nucl. Phys. B 650, 391 (2003) [hep-ph/0206071].
 H. C. Cheng, J. L. Feng and K. T. Matchev, Phys. Rev. Lett. 89, 211301 (2002)
 J. A. R. Cembranos, A. Dobado and A. L. Maroto, Phys. Rev. Lett. 90, 241301
 J. A. R. Cembranos, A. Dobado and A. L. Maroto, Phys. Rev. D 68, 103505
 J. L. Feng, A. Rajaraman and F. Takayama, Phys. Rev. Lett. 91, 011302 (2003)
 J. L. Feng, A. Rajaraman and F. Takayama, Phys. Rev. D 68, 063504 (2003)
 J. L. Feng, A. Rajaraman and F. Takayama, Phys. Rev. D 68, 085018 (2003)
 For recent reviews of neutralino dark matter, see, for example, J. L. Feng,
eConf C0307282, L11 (2003) [hep-ph/0405215]; M. Drees, these proceedings,
hep-ph/0410113; M. Peskin, these proceedings; N. Spooner, these proceedings;
X. Tata, these proceedings.
 J. R. Ellis, K. A. Olive, Y. Santoso and V. C. Spanos, Phys. Lett. B 588, 7 (2004)
 W. Buchmuller, K. Hamaguchi, M. Ratz and T. Yanagida, Phys. Lett. B 588, 90
 F. Wang and J. M. Yang, hep-ph/0405186.
 J. L. Feng, S. Su and F. Takayama, Phys. Rev. D 70, 063514 (2004)
 J. L. Feng, S. Su and F. Takayama, hep-ph/0404231.
 J. L. Feng, A. Rajaraman and F. Takayama, hep-th/0405248.
 J. R. Ellis, K. A. Olive, Y. Santoso and V. C. Spanos, hep-ph/0408118.
 L. Roszkowski and R. R. de Austri, hep-ph/0408227.
 For other scenario with very long-lived particles, see, e.g., Ref.  and X. J. Bi,
M. z. Li and X. m. Zhang, Phys. Rev. D 69, 123521 (2004) [hep-ph/0308218].
 H. Pagels and J. R. Primack, Phys. Rev. Lett. 48, 223 (1982).
 S. Weinberg, Phys. Rev. Lett. 48, 1303 (1982).
 L. M. Krauss, Nucl. Phys. B 227, 556 (1983).
 D. V. Nanopoulos, K. A. Olive and M. Srednicki, Phys. Lett. B 127, 30 (1983).
 M. Y. Khlopov and A. D. Linde, Phys. Lett. B 138 (1984) 265.
 J. R. Ellis, J. E. Kim and D. V. Nanopoulos, Phys. Lett. B 145, 181 (1984).
 J. R. Ellis, D. V. Nanopoulos and S. Sarkar, Nucl. Phys. B 259, 175 (1985).
 R. Juszkiewicz, J. Silk and A. Stebbins, Phys. Lett. B 158, 463 (1985).
 J. R. Ellis, G. B. Gelmini, J. L. Lopez, D. V. Nanopoulos and S. Sarkar, Nucl.
Phys. B 373, 399 (1992).
 T. Moroi, H. Murayama and M. Yamaguchi, Phys. Lett. B 303, 289 (1993).
 M. Bolz, A. Brandenburg and W. Buchmuller, Nucl. Phys. B 606, 518 (2001)
 For a review of cosmological constraints on late decays, see M. Y. Khlopov, Cos-
moparticle Physics, Singapore: World Scientific, 1999.
 S. Burles, K. M. Nollett and M. S. Turner, Astrophys. J. 552, L1 (2001)
 J. A. Thorburn, Astrophys. J. 421, 318 (1994).
 P. Bonifacio and P. Molaro, MNRAS, 285, 847 (1997).
 S. G. Ryan, T. C. Beers, K. A. Olive, B. D. Fields and J. E. Norris, Astrophys.
J. Lett. 530, L57 (2000) [astro-ph/9905211].
 M. H. Pinsonneault, T. P. Walker, G. Steigman and V. K. Narayanan, Astrophys.
J. 527, 180 (1999) [astro-ph/9803073].
 S. Vauclair and C. Charbonnel, Astrophys. J. 502, 372 (1998) [astro-ph/9802315].
 M. Kawasaki and T. Moroi, Astrophys. J. 452, 506 (1995) [astro-ph/9412055].
 E. Holtmann, M. Kawasaki, K. Kohri and T. Moroi, Phys. Rev. D 60, 023506
 M. Kawasaki, K. Kohri and T. Moroi, Phys. Rev. D 63, 103502 (2001)
 R. H. Cyburt, J. R. Ellis, B. D. Fields and K. A. Olive, Phys. Rev. D 67, 103521
 M. H. Reno and D. Seckel, Phys. Rev. D 37, 3441 (1988).
 S. Dimopoulos, R. Esmailzadeh, L. J. Hall and G. D. Starkman, Astrophys. J.
330, 545 (1988).
 S. Dimopoulos, R. Esmailzadeh, L. J. Hall and G. D. Starkman, Nucl. Phys. B
311, 699 (1989).
 K. Kohri, Phys. Rev. D 64, 043515 (2001) [astro-ph/0103411].
 K. Jedamzik, astro-ph/0402344.
 M. Kawasaki, K. Kohri and T. Moroi, astro-ph/0402490.
 M. Kawasaki, K. Kohri and T. Moroi, astro-ph/0408426.
 J. L. Feng, S. Su and F. Takayama, these proceedings, hep-ph/0410119.
 W. Hu and J. Silk, Phys. Rev. Lett. 70, 2661 (1993).
 D. J. Fixsen et al., Astrophys. J. 473, 576 (1996) [astro-ph/9605054].
 S. Eidelman et al. [Particle Data Group Collaboration], Phys. Lett. B 592, 1
 M. Drees and X. Tata, Phys. Lett. B 252, 695 (1990).
 J. L. Goity, W. J. Kossler and M. Sher, Phys. Rev. D 48, 5437 (1993)
 A. Nisati, S. Petrarca and G. Salvini, Mod. Phys. Lett. A 12, 2213 (1997)
 J. L. Feng and T. Moroi, Phys. Rev. D 58, 035001 (1998) [hep-ph/9712499].
 K. Hamaguchi, Y. Kuno, T. Nakaya and M. M. Nojiri, hep-ph/0409248.
 J. L. Feng and B. T. Smith, hep-ph/0409278.
 F. E. Paige, S. D. Protopescu, H. Baer and X. Tata, hep-ph/0312045.