Download Slides - Indico

Dr. Nicolò Masi
- Bologna University and INFN
May 20th 2014
On Earth Detection
• The possibility to detect the recoil energy of the nuclei of a low–background detector as a
consequence of their elastic scattering with a WIMP.
• The signal arises if the solar system itself is moving relative to the stationary halo of WIMP
as it orbits around the Milky Way center.
• This recoil can be detected in
some ways :
 Electric charges released
(ionization detector)
 Flashes of light produced
(scintillation detector)
 Vibrations produced (phonon
detector)
Scattering
Rate
Local DM
density
𝑅𝑎𝑡𝑒 =
𝜌0
𝑚𝜒 𝜎𝑣
𝜌0 = 0.3 ÷ 0.4 𝐺𝑒𝑉 ∙ 𝑐𝑚−3
Earth Velocity
through the DM Halo
𝑣0 = 220 𝑘𝑚/𝑠
Elastic cross section (SI):
Nuclear Form Factor
Differential Recoil
Energy Spectrum
Integral over local
WIMP velocity
distribution
Low energy effective Lagrangian for WIMP-quark interaction
L  f q (  )  (qq)  dq (   5  )  (q  5q)  ....
scalar interaction
spin-dep. interaction
q
q
q
q
• The other terms are velocity-dependent contributions and can be
neglected in the non-relativistic limit for the direct detection.
• The scalar interaction scales with a power of the the atomic
weight and almost always dominates for nuclei with A > 30.
Hypothetical WIMP-Nucleon Scattering: a Summary
Spin-dependent SD and
Spin-independent SI
interaction
• In the Feynman diagrams,
scalars are represented by
dashed lines, fermions by solid
lines and vector bosons by
wavy lines.
• The mediators , h, Z' and SM
Z and h are neutral under both
electromagnetism and color,
while X, and Q (quarks)
transform as triplets under
color and carry electric charge
Research Landscape
Direct Search of Dark Matter: Constraints
Circumstantial signals
/H
For M>10 GeV
the WIMP/Axion
Spin Independent
Nucleon cross
section should be
less than
10−44 𝑐𝑚2
Anything above the blue lines
is now excluded
1000
A hope only for very massive candidates
It won’t be forever
LUX currently holds
the leader position
for DM masses above
6 GeV; the Xenon
collaboration is
already preparing a
nuclear response in
the form of a 3 ton
detector. Meanwhile,
the SuperCDMS
experiment will
secure a monopoly in
the low-mass region.
Direct detection experiments will inevitably hit the neutrino wall: they will reach the sufficient
sensitivity to observe nuclear recoils due to elastic scattering of solar and atmospheric
neutrinos. That will constitute an irreducible background to dark matter searches (unless
directional detection techniques are developed).
There are also stringent bounds from IceCube for
the Spin-dependent DM cross-section….
𝝈𝑺𝑫 < 𝟏𝟎−(𝟒𝟏÷𝟒𝟎) 𝒄𝒎𝟐
The principle: WIMPs could be gravitationally captured by massive objects like the Sun and
accumulate in the core the Sun itself: for high enough density they would annihilate
producing neutrinos, which could be observed by IceCube
...that can be related to the parameters space of different DM
models, such as the Universal Extra Dimension Model (UED):
10-5 pb = 10-41 cm2
SI vs SD
Collider Search:
Direct Detection Experiments vs LHC
Collider Detection: Interaction Cross Section limits
 Look for missing energy signatures.
 Problem:
Can only find DM candidate (no proof that it is DM)
 Model-dependent strategy: Cascade decays with ET
CMS Results
ATLAS Results
A Corotating Dark Disk:
do our assumptions survive?
Dark Structures
Dark Matter Disk
Also low energy signals could be TeV-ish Dark Matter hints
• If the dominant dark matter contribution to the local high energy e flux comes from a Dark
Disk rather than the spherical halo, we get good fits of Fermi and PAMELA’s data;
• the boost factor/Sommerfeld enhancement is almost an order of magnitude smaller than
what is needed for the standard fits;
• a (perhaps) corotating DD with small velocity v0 = 50 ÷ 70 km/s is provided by structure
formation simulations of standard ΛCDM cosmology in presence of baryons.
The dynamical friction analysis
shows that DAMA/LIBRA annual
modulation data and CDMS-II
excesses could correspond to a
dark matter with
3 𝑇𝑒𝑉 ≲ 𝑚𝐷𝑀 ≲ 10 𝑇𝑒𝑉
Dark Matter Candidates:
not only an astrophysical necessity
Main theoretical Standard Model problems
 Hierarchy problem – the mass of the Higgs gets some very large quantum corrections due to
the presence of virtual particles (mostly virtual top quarks). These quadratic corrections are
much larger than the actual mass of the Higgs. The bare mass parameter of the Higgs must be
unnaturally fine tuned in such a way that almost completely cancels the quantum corrections.
 Strong CP problem – theoretically it can be argued that the SM should contain a term that
breaks CP symmetry in the strong interaction sector. Experimentally, however, no such violation
has been found, implying that the coefficient of this term is very close to zero. This fine tuning
is also considered unnatural.
 Neutrino masses – according to the SM, neutrinos are massless particles. However, neutrino
oscillation experiments have shown that neutrinos do have mass. Mass terms, added by hand,
need to be extraordinarily small and it is not clear if the neutrino masses would arise in the
same way that the masses of other fundamental particles do in the Standard Model.
 Matter/antimatter asymmetry – The universe is made out of mostly matter. However, the
SM predicts that matter and anti-matter should have been created in (almost) equal amounts,
if the initial conditions of the universe did not involve disproportionate matter relative to
antimatter.
If DM would solve one (or more than
one) of these problems, everything
would be more consistent and natural
Exotic Candidates
Neutralino 𝝌
WIMP Mass Region: 100 GeV ÷ 10 TeV
(<100 TeV)
Statistic: dirac or majorana
fermion, boson
S= 0,1/2, 1, 3/2, 2
Axion Mass Region:
10 μeV÷1 meV
SUSY
• The gauge hierarchy problem is most elegantly solved by supersymmetry.
• In SUSY models every SM particle has a new, as-yet-undiscovered partner particle, which has
the same quantum numbers and gauge interactions, but differs in spin by 1/2.
• The introduction of new particles with opposite spin-statistics from the known ones
supplements the SM quantum corrections to the Higgs boson mass with opposite sign
contributions:
MSSM: Neutralino
•The exact properties of each neutralino will depend on the details of the mixing but
they tend to have masses in the order of 300-600 GeV and couple to other particles
with strengths characteristic of the weak interaction.
•In this way they are phenomenologically similar to neutrinos. In fact they are
Majorana fermions and not directly observable in particle detectors at accelerators.
Some MSSM
Parameters
In the basis
0
0
0
0
( B,W 0 , H 10, H 02 ):  i  Ni1 B  Ni 2W  N i 3 H 1  N i 4 H 2

- ratio of vev of the two neutral Higgs
- Bino, Wino mass parameters
- Higgsino mass parameter
The mixing
matrix
SUSY
dependence: 5
independent
parameters
Upper bounds now enlarged by LHC results
Neutralino: Classification & Annihilation Channels
Gaugino
Higgsino
Mixed
𝒂𝒏𝒕𝒊𝒅𝒆𝒖𝒕𝒆𝒓𝒐𝒏𝒔
Main Models
SUSY Constrained
The exclusion region in the CMSSM (Constrained MSSM) framework, using
charge di-leptons, is narrowing SUSY chances…
Discrimination parameter I𝜙
for signal and background:
the AMSB Wino MSSM is
the most suitable for
AMS-02, both in antiproton
and positron channels
Expected clear
positron signal
from heavy Wino
25
SUSY Gravitino
• The gravitino is not a WIMP, but it is a viable dark matter candidate.
• The gravitino is the supersymmetric partner of the graviton. If it exists, it is a
fermion of spin 3⁄2 and therefore obeys the Rarita-Schwinger equation.
• If supersymmetry is to solve the hierarchy problem of the Standard Model,
the gravitino cannot be more massive than about 1 TeV (preferably light).
• It’s a strange candidate, the only high spin candidate, which give a lot of
cosmological problems and it’s not able to produce the correct actual dark
matter density of our Universe. It has also a low annihilation cross section and
it’s a superpartner of an hypothetical particle, the graviton, which could not
exist at all.
Possible Gravitino Indirect Detection in Multiple Channels
e+
𝜸
antiproton
A low signal,
compatible with
the observed
antiproton flux: a
hidden signal?
Little Higgs Theory
• As an alternative mechanism to Supersymmetry to stabilize the weak scale, the socalled “Little Higgs” model, has been proposed and developed: the Standard Model
Higgs becomes a pseudo-Goldstone boson with its mass protected by an approximate
nonlinear global T-symmetry.
• Although the idea was first suggested in the 1970s, aviable model was only constructed
by Nima Arkani-Hamed, Andy Cohen, and Howard Georgi in the spring of 2001.
• Little Higgs theories were an outgrowth of dimensional deconstruction: in these
theories, the gauge group has the form of a direct product of several copies of the same
factor, for example SU(3) × SU(3).
• In the Minimal Moose model these symmetries acquires a clear physical attribute:
they’re a chiral symmetry SU(3)L × SU(3)R and a collective spontaneous symmetry
breaking produces the vector subgroup from which the Standard Model descends.
• The quadratic divergence of Higgs mass is removed using bosonic loops with opposite
hypercharge. The divergences which remain are present only at the two-loop level: the
weak scale can be stabilized in an effective field theory which is valid up to  10 TeV.
Little Higgs Spectrum
Massive LTP Photon
Annihilation
e+
Little Higgs
Dark Matter parameters
space:
The region above the line can be
distinguished from the background:
AMS can sweep a wide window
30
Scalar Singlet/Multiplet
 Predictivity and simplicity are
undoubtedly their most salient
features.
 In contrast with other common
scenarios that explain the dark
matter, it contains only one or
few additional fields, the singlet
scalar/multiplet, and few new
parameters: the singlet mass and
the coupling between the singlet
and the Higgs boson.
Scalar Singlet/Multiplet
The area above the MIN, MED,
MAX lines is detectable by AMS-02
in the antiproton channel
32
Kaluza –Klein Theory: UED
• In UED all particles propagate in flat, compact extra dimensions of size 10-18 m or
smaller.
• In the simplest UED model, minimal UED, there is one extra dimension of size R
compactified on a circle.
• Every SM particle has an infinite number of partner particles, with one at every KaluzaKlein (KK) level n, with mass  nR-1. In contrast to supersymmetry, these partner
particles have the same spin. As a result, UED models do not solve the gauge hierarchy
problem.
• The simplest UED models preserve a discrete parity known as KK-parity, which implies
that the lightest KK particle (LKP) is stable and a possible dark matter candidate: a heavy
vector boson.
• Another particle produced by the KK theory spectrum is the LZP, i. e. a right-handed
neutrino which also may account for the dark matter observations.
• Kaluza-Klein dark matter particles, unlike neutralinos or Little Higgs dark matter, can
annihilate efficiently to light fermions.
• KK particles may escape from collider events following the fourth spatial dimension
(missing energy channel)
KK Warped GUT LZP
M = 40÷50 GeV
theoretical
signal
Kaluza-Klein Theories: Universal Extra Dimension
Positron High
Energy Signal
Antiproton High
Energy Signal
Other Attempts
Primordial Quantum Black Holes
• Micro black holes are predicted as tiny black holes, also called quantum mechanical black
holes or mini black holes. They could be produced at LHC.
• It is possible that such quantum primordial black holes were created in the high-density
environment of the Early Universe.
• They might be observed by astrophysicists in the near future, through the particles they are
expected to emit by Hawking radiation.
Sensitivity problem: not a good candidate
Not
observed
Antiproton
Antideuteron
From CMS results, as of March 2012, PBH
should have masses above 3.8 to 5.3 TeV
Light Sterile Neutrinos (Warm DM)
• These hypothetical particles are similar to Standard Model neutrinos, but without Standard
Model weak interactions, apart from mixing.
• They were proposed as dark matter candidates in 1993 by Dodelson and Widrow.
• Stringent cosmological and astrophysical constraints on sterile neutrinos come from the
analysis of their cosmological abundance and the study of their decay products: light
neutrinos, with masses below a few keV, would be ruled out as dark matter candidates.
• Sterile neutrinos could also be cold dark matter, if there is a very small lepton asymmetry, in
which case they are produced resonantly with a non-thermal spectrum.
4th SM generation MDM
• The Minimal Dark Matter adds to the SM the minimal amount of new physics (just one
extra EW multiplet X) and search for the minimal assignments of its quantum numbers
(spin, isospin and hypercharge). The stability of the successful candidates is guaranteed
by the SM gauge symmetry and by renormalizability.
• MDM is strongly disfavored from searches at LEP (neutrino’s three family bound), and
from the LHC and Tevatron searches of the Higgs: MDM models need heavy Higgs (about
0.5 TeV), incompatible with our light Higgs with a mass of ∼ 125 GeV.
Singlino
• NMSSM is an acronym for Next-to-Minimal Supersymmetric Standard Model, a
supersymmetric extension to the Standard Model that adds an additional singlet
chiral superfield to the MSSM.
• The spin-1/2 singlino 𝑆 gives a fifth neutralino, compared to the four neutralinos
of the MSSM.
• The singlino does not couple to gauge bosons, leptons, sleptons, quarks or
squarks.
• In the case the singlino is the lightest supersymmetric particle (LSP) all
supersymmetric partner particles eventually decay into the singlino. Due to R
parity conservation this LSP is stable. In this way the singlino could be detected
via missing transversal energy in the detector
Graviton
• The graviton is a hypothetical elementary particle that mediates the force of gravitation in the
framework of quantum field theory.
• The graviton is expected to be massless (because the gravitational force appears to have
unlimited range) and must be a spin-2 boson. The spin follows from the fact that the source of
gravitation is the stress–energy tensor, a second-rank tensor (compared to electromagnetism's
spin-1 photon, the source of which is the four-current, a first-rank tensor).
• Any massless spin-2 field would give rise to a force indistinguishable from gravitation, because
a massless spin-2 field must couple to the stress–energy tensor in the same way that the
gravitational field does.
• They would have extremely low cross section (almost zero) for the interaction with matter:
individual gravitons detection is not possible.
• String theory predicts the existence of gravitons and their well-defined interactions: a graviton
is a closed string in a very particular low-energy vibrational state.
• As closed strings without endpoints, they would not be bound to branes and could move freely
between them: if we live on a brane this "leakage" of gravitons from the brane into higherdimensional space could explain why gravitation is such a weak force.
• Gravitons from other branes adjacent to our own could provide a potential explanation for
dark matter.
• Experiments to detect gravitational waves, which may be viewed as coherent states of many
gravitons, are underway (LIGO and VIRGO): they might provide information about certain
properties of the graviton, such as its mass.
Ambitious Theories:
DM solving other fundamental problems
Asymmetric Theories: Tulin X antibaryonic DM
Asymmetric DM theories take into account the possibility of a DM internal matterantimatter asymmetry, introducing a DM sector with SM-like violations.
A unique Theory for Dark Matter and
Antimatter: a X postreheating particle
especially decays into visible material
hadronic/leptonic world and dark antibaryonic
antimatter (Φ and 𝑌)
IND: Indirect
Nucleon Decay
And meson may decay into
detectable leptons
Shaposhnikov Neutrinos
Advantages of Shaposhnikov Theory
…It solves many problems and implies
that no new high-mass particle physics
lies in ambush up to Planck Scale
SHIP in a new proposal for a beam dump experiment at CERN-SPS for
hidden Shaposhnikov particles
State of Art: DM Candidates Landscape
LHC
LHCb
Little portion of
parameter space remains
Only Standard
Model ?!
ATLAS Results
𝑞∗
𝑄𝐵𝐻
𝑊′
𝑆𝑅
A Great Desert
Table 1 - DM Candidates properties
HS: Hidden Sector
Also leptophilic
models may
produce antip by
EW corrections
Wrong relics
Light candidates
Scalar, vector, Dirac fermion,
Majorana fermion, RaritaSchwinger fermion
GHP: most relevant
S=0,1 Bosons and Majorana Fermions are the
most interesting candidates because they’re their
own antiparticle and so capable to self-annihilate
Table 2 - DM Candidates detection
An independent model
Difficult to prove
Higgs Portal
Model
Also the HS
depends on SUSY!
Hidden Sector and Hidden Valley Models generate armies of dark particles including
the Dark Photon: does the visible photon have a counterpart, a dark photon, that
interacts with the components of dark matter?
Without SUSY
Little Higgs, KK Theory, Graviton, Singlet/Multiplet Scalar,
Axion, MDM, PBH, Sterile Neutrino, Antibaryonic DM…
With only our 4 dimensions
Little Higgs, Singlet Scalar, Axion...
Detectable with AMS-02:
Little Higgs and Singlet/Multiplet Scalar
Remarks: a heavy WIMP Identity Card
 The positron signal is the fundamental channel for DM study. In terms of intensity of
annihilation products fluxes: space experiments can see a positron peak for all DM
candidates capable of producing e+ beyond 100 GeV, testing all DM theories.
 AMSB Wino-like neutralino, UED KK LKP particle, Scalar Multiplet and Little Higgs LTP
are the most suitable candidates for Earth and space experiment. The first three could be
non-leptophilic theories capable to grant a very heavy candidate producing high energy
antiproton fluxes measurable by AMS-02; but SUSY and KK UED theory are quite
disfavored if a simplicity criterion is invoked and once taken into account LHC evidences.
Parameters space for a
non-leptophilic candidate
New TeV-ish paradigm:
1 𝑇𝑒𝑉 < 𝑀𝐷𝑀 < 10 𝑇𝑒𝑉
Astrophysical and cosmological constraints: compact stars, galaxies clusters, CMB… :
DIRECT CONSTRAINTS:
XENON100 + EDELWEISS + ICECUBE:
CR Fluxes for kinetic
energy of
100 ÷ 2000 𝐺𝑒𝑉/𝑛
with DM
without DM
𝜒𝑁
𝜎𝑆𝐼 < 10−45÷44 𝑐𝑚2
𝜒𝑁
𝜎𝑆𝐷 < 10−39÷38 𝑐𝑚2
fraction with DM
fraction without DM
20÷30
5÷10%
Axions:
a Bit of Detergent
Neutron Electric Dipole
Moment
Peccei-Quinn Idea:
Theta is a new
particle field
EM Anomaly
Kinetic term
From Goldstone Theorem:
QCD Instanton
Sector
Pseudo Nambu-Goldstone Boson of the
PQSB: its vev remove the anomaly,
through a potential minimum
Currents
Maxwell-Chern-Simons
Equations
Light shining
through walls
experiments
From CDM to BEC
a
a
a
Axions rethermalize
and reach TBEC
a
 v  0
 v  0
Galactic Halos: Tidal Torque
Theory
fa – Hinfl Plots :
Experimentally
excluded regions
(colored ones)
Axions production, with the so-called
«misallignament angle», and their properties
are strongly correlated with Inflation physics
and primordial gravitational waves…
Perspective after BICEP2
What does this have to do with axion dark matter?
There were big uncertainties in the possible properties on axions, depending on whether they
were created before or after inflation. The observation by BICEP-2 rules out the creation of
axion dark matter before inflation, giving a more precise target for future axion searches.
A narrow
window
Axion Searches
 Light Shining Through Wall (BFRS and PVLAS) - In the Italian PVLAS experiment polarized
light propagates through the magnetic field of a 5 T dipole magnet, searching for a small
anomalous rotation of the direction of polarization: if axions exist, photons could interact
with the field to become virtual or real axions. This rotation is very small and difficult to
detect, but this problem can be overcome by reflecting light back and forth through the
magnetic field millions of times.
 Axions can be produced in the Sun's core when X-rays scatter off electrons and protons in
the presence of strong electric fields and are converted to axions via Primakoff effect. The
CAST experiment is currently underway to detect these axions by converting them back to
x-rays in a strong magnetic field.
 The USA Axion Dark Matter Experiment (ADMX) searches for light, weakly interacting
axions saturating the dark matter halo of our galaxy.ADMX is a strong magnetic field
permeating a cold microwave cavity. Axions matching the resonant frequency of the
cavity decay into microwave photons.
 New italian proposal for an experiment which exploits the axion-electron conversion in
the detector, using the galactic axion wind.
 Magnetars could convert photons to axions much more efficiently than most laboratory
experiments, over a broad axion mass range. This, in turn, would give rise to distinct
absorption-like features in the spectra of such extreme objects which can be observed by
current telescopes.
ADMX
ADMX will soon be sensitive to even
the more weakly coupled dark matter
axions in the range 1μeV to 20μeV.
• Dark Matter is the simplest and most clever way to deal with astrophysical,
cosmological and Standard Model problems: DM has to exist!
• On Earth experiments are reaching technical limits, whereas indirect searches are still
promising for heavy WIMPs
• Nuclear uncertainties affect every sector of particle physics: DM direct detection
(nuclear recoil matrix), indirect searches (spallation in the ISM) and cosmology
(primordial nucleosynthesis)
• A deep study of the dark matter profile and its hypothetical dark disk is challenging but
fundamental
• Exotics candidates, SUSY candidates and SUSY antagonist: a full exhaustive theory
which accounts for Dark Matter and fundamental SM problems in not available yet
• We prefer: minimal scalar and Majorana-like solution, deriving from a Strong or EW
Simmetry Breaking, with TeV-ish masses
• A viable alternative scenario is constitued by the tiny axion, but this field of search is
still at an embryonic state
• AMS-02 will soon demonstrate the presence or absence of WIMPs annihilation
products
Some open questions
 DM really dark or only shady? - in some theories it has an electric or
magnetic dipole moment: maybe this is only a human experimental limitation and
not a physical interaction veto. Can we study an electromagnetic DM cross section
from CMB polarization?
Only a Dirac fermion could have an electric or magnetic dipole moment!
 We usually imagine a self-annihilating Majorana particle, when we talk about DM.
But we don’t know if Majorana particles truly exist and, if not, we have
to invoke uncommon and fine-tuned decaying channels.
 Can we contemplate WIMP oscillations
- a fundamental flavour 𝜈-like
oscillation or a neutral meson-like matter/antimatter
oscillation - or an induced β+
like decay (similar to 𝑝 + 𝜈 → 𝑛 + 𝑒 )? Would they generate a correct amount of
cosmic particles?
 Is it possible to create a link between the DM cross sections, i.e.
nuclear, annihilation/decay cross section and the hypothetical EM one?