Download Hidden Sector Dark Matter in String/M theory.

Hidden Sector Dark Matter in String/M
theory.
Bobby Samir Acharya
International Centre for Theoretical Physics
and King’s College London
String Pheno 2016, Ioannina, June 2016
Based on
arXiv:1604.05320
work with:
S.A.R. Ellis, G. Kane, B. Nelson, M. Perry
and
arXiv:1606.xxxx to appear.
and
work in progress with M. Fairbairn and E. Hardy
Dark Matter and Motivation
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Dark Matter evidently exists
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We know very little about its
properties
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Its thus important to propose
models for what dark matter
could be
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This will hopefully lead to
testable predictions from which
we will learn something
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What about Dark Matter in the
String/M theory context?
Dark Matter and String Theory
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What can string/M theory say
about Dark Matter?
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String/M theory is replete with
hidden sectors.
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Is Dark Matter in the Hidden
Sector?
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If so, can we build reasonable
models for Dark Matter within
the String/M theory framework?
Dark Matter and String Theory
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We will address the question is
Dark Matter in the Observable
Sector?
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Answer: Probably not.
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Will go on to try and (crudely)
classify hidden sector DM
models in string/M theory
(work in progress)
Hidden Sector Definition
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Definition: A hidden sector is one with no Standard Model
gauge interactions at tree level.
Hidden Sectors are Generic
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Heterotic: the other E8
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Type IIA/IIB: different D-brane sectors, often required for
global consistency
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M/F -theory: often singular loci supporting hidden sector
particles (cf Grassi/Halverson/Taylor/Morrison et al)
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CFT scans often lead to hidden sectors being typical. See e.g.
papers of Kounnas, Leontaris, Rizos et. al.
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G2 manifolds with large b2 give rise to lots of hidden sector
U(1)s.
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In general it is difficult to find string/M theory
compactifications without hidden sectors.
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So we will conservatively assume that Hidden Sectors exist.
Observable Sector Dark Matter Stability?
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In many models, DM is a neutral WIMP (a stable, massive
particle with SU(2) × U(1)Y interactions)
Usually this particle is stable due to a discrete symmetry
which prevents it from decaying
In the MSSM the standard example is the LSP and the
discrete symmetry is R-parity.
A key point is that the WIMP, χ will be the lightest particle
charged under the discrete symmetry.
BUT: with hidden sectors present, χ also has to be
lighter than the hidden sector states.
There is apparently no good argument which states that the
lightest charged state is in the observable sector.
If there were such an argument, you could equally well apply it
to the hidden sectors, which leads to a contradiction.
Therefore: discrete symmetries can not generally guarantee
the stability of observable sector particles.
Observable Sector Particles Decay into the Hidden
Sector
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Constraints from direct and indirect DM detection also
indicate that DM is in the hidden sector
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This would require WIMPs (e.g. the LSP) to decay
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Sizeable enough R-parity violation is difficult to achieve
typically in global models
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How could observable sector particles decay into the hidden
sector?
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This requires a sizeable coupling between OS and HS particles.
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But the hidden sector is hidden, is it not?
Hide and Seek
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Massive string/brane states exist which physically connect
different gauge sectors
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e.g. open strings which stretch between physically separated
D-brane stacks.
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e.g. M2-branes wrapped on surfaces which intersect two
distinct codimension four orbifold singularities
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These correspond at low energies to massive particles which
are charged under both gauge groups
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If the hidden sector contains an unbroken U(1), then
integrating out such states will lead to U(1) − U(1)Y mixing
between the hidden and hypercharge gauge boson in the low
energy theory:
U(1)
L ∼ Fµν FYµν
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This is well known and has been studied in many examples
over the years, e.g. Dienes, Kolda and March-Russell 97
Kinetic U(1) − U(1)Y mixing
leads to ∼
ga gb
12π 2
log(
2
M 2 +∆Mab
)
M2
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For O(1) mass splittings, e.g. if ∆M ∼ M ∼ MGUT ,
∼ 10−2 − 10−3
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For low-scale breaking, e.g. radiative breaking, can be
VERY small, leading to long lived states.
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This case looks very much like the SUSY WIMP scenario and
is now severely constrained
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We will focus on the (presumably more typical) former case
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There can also be similar effects with the Higgs portal i.e.
L ∼ HH † φφ† but we didnt look at those in detail.
Observable Sector Particles Decay into the Hidden
Sector
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These mixings will connect many apparently hidden gauge
sectors to one another
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A sort of web of portal interactions is generated
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The lightest state in one sector will then decay into lighter
states in other sectors
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In this picture, unless there is an accident, the Lightest
Observable Sector Particle (LOSP) will decay into the
hidden sector
Decays in General
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The LOSP decays are dominated by χLOSP → Z + χhidden and
h + χhidden
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NOTE: χhidden need NOT be Dark Matter
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χhidden → ..χDM + other hidden sector states
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Can even have χhidden → ..χDM + Standard Model states
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These typically all have small lifetimes, τ ≤ 10−6 s
Decays in General
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Description in Type IIB and LVS scenario
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With multiple D7 and/or D3 sectors, observable sector
gauginos could be heavier than hidden ones.
So, what is Dark Matter?
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Given that DM is most likely to be in the hidden sector, what
could it be?
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A priori, any suitably stable hidden sector particle could be a
candidate
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The main constraint is that it is not overproduced
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So far, we have said nothing atall about the production of
Dark Matter
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We will require that it fits into the non-thermal dark matter
picture in which moduli fields dominate the energy density of
the Universe prior to Big Bang Nucleosynthesis.
Cosmological Moduli Problem Reminder
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Supersymmetry, Cosmology and New TeV Physics - Pagels,
Heinz et al. Phys.Rev.Lett. 48 (1982) 223 UCSC-TH-141-81
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Cosmological Constraints on the Scale of Supersymmetry
Breaking - Weinberg, Steven Phys.Rev.Lett. 48 (1982) 1303
Print-82-0306 (TEXAS)
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Cosmological Problems for the Polonyi Potential - Coughlan,
G.D. et al. Phys.Lett. B131 (1983) 59 LA-UR-83-1423
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On the Axion, Dilaton, Polonyi, Gravitino and Shadow Matter
Problems in Supergravity and Superstring Models - Ellis, John
R. et al. Phys.Lett. B174 (1986) 176 CERN-TH-4409/86
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In string theory: B. de Carlos, J. A. Casas, F. Quevedo and
E. Roulet, Model independent properties and cosmological
implications of the dilaton and moduli sectors of 4-d strings,
Phys. Lett. B 318 (1993) 447 [hep-ph/9308325].
Cosmological Moduli Problem Reminder
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Moduli masses mφ ∼ m3/2
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Moduli, being very weakly coupled scalar fields (mpl
suppressed) dominate the energy density of the early Universe
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Lifetime τφ ∼
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This is during Big Bang Nucleosynthesis, BBN.
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Moduli decays inject charged particles and hadrons into the
plasma, disassociating nuclei, changing the relative
abundances of light elements
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This is the Cosmological Moduli Problem
2
mpl
3
mφ
3
∼ O(0.1)sec ( TeV
mφ )
Non-thermal Dark Matter Reminder.
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In the last few years we argued that non-thermal dark matter
is a generic prediction of string/M theory models with low
energy supersymmetry breaking
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The arguments were simply:
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The cosmological moduli problem implies moduli will
dominate the energy density of the universe
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The pre-BBN Universe is MATTER DOMINATED
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The cosmological moduli problem goes away if
mφ ∼ m3/2 ∼O(10) TeV
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The moduli decays before BBN significantly dilute any prior
relics
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Dark Matter is non-thermally produced
Non-thermal Dark Matter, Benchmark Model.
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MSSM with squark and slepton masses of order m3/2 ∼ 50TeV
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Gaugino masses of order 0.1 - few TeV
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Neutral W-ino LSP, with mass of order 0.2 TeV
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Moroi-Randall, G2-MSSM, ..
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The W-ino dark matter arises from the decay of moduli
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This is now ruled out by Fermi-LAT data (Fan/Reece, ..) if
W-inos make up more than 20 percent of DM
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In any case, we have argued that these are unstable to hidden
sector decays.
So, what is Dark Matter? A crude classification.
arXiv:1607.xxx to appear
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mφ
2
mpl
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When the moduli decay ρUniverse ∼
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This gives ρDM ∼ ρUniverse Br (φ → DM)
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0
Initial number density nDM
=
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H
hσv i
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0
Annihilation scenario nDM
≥
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0
Branching scenario nDM
∼
3
mφ
2 .
hσv impl
ρDM
mDM
Two cases:
H
hσv i
H
hσv i
can be compared to
Branching Scenario
H
hσv i
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Branching scenario nDM
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In Branching scenario, the moduli decay has to produce the
correct amount of Dark Matter
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Constrains the product of the branching ratio and DM mass
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A simple, weakly coupled example would be a chiral fermion
in the hidden sector with appropriate mass
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The fermion should have a suitably small annihilation
cross-section, but this is straightforward if this hidden sector is
suitably hidden.
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We have examples of what such sectors would look like in the
forthcoming paper.
Annihilation Scenario
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H
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Annihilation scenario nDM
hσv
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In this case, the initial DM density is large enough for the DM
to self-interact
One has to arrange that hσv i allows DM to annihilate to
H
reduce the number density to hσv
i
The problem here is that if the hidden sector is hidden,
annihilating into hidden sector states does not reduce the DM
density unless
a) the annihilation products are unstable and decay into the
Standard Model
b) hσv i has important contributions from N → 2 processes
a) requires structure in the DM sector, rather like the SM
a) is constrained by e.g. indirect detection data
b) can arise if DM sector is an IR strongly coupled theory e.g.
a QCD-like theory
More details will appear in the paper.
Annihilation Scenario
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a) the annihilation products are unstable and decay into the
Standard Model
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b) hσv i has important contributions from N → 2 processes
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a) requires structure in the DM sector, rather like the SM
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a) is constrained by e.g. indirect detection data
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b) can arise if DM sector is an IR strongly coupled theory e.g.
a QCD-like theory
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b) studied in thermal case recently by Boddy et. al
(1402.3629, 1408.6532), Hochberg et.al (1411.3727),
Buen-Abad et al (1505.03542) and important early work of
Carlson, Machachek and Hall.
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We are studying it in the non-thermal case with M. Fairbairn
and E. Hardy.
A Prediction for the LHC
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A gluino will first decay to q q̄+χMSSM
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Then χMSSM → Z /h + χhidden +
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Then χhidden → χDM +Standard Model pairs.
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SO: pp → g̃ g̃ → t t̄t t̄ + ZZ + 4l!!
Conclusions
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WIMPs can easily decay into hidden sectors in general
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Dark Matter is presumably in the hidden sector
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Cosmological Moduli physics implies that DM is non-thermally
produced
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Classified into Branching and Annihilation scenarios
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Both scenarios seem to require structure in the dark sector:
non-trivial interactions, dynamics, mass hierarchies
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I wonder if a dark sector superstring theorist would have
concluded the same thing about the hidden Standard Model
sector:)
uχαρiστ ω!