Dark Matter ReviewMariana Vargas-Magaña

TASI 2014 LECTURES: THE HUNT FOR DARK MATTER

arXiv:1502.01320v2 10 Jun 2015

Outline• Evidence of DM

• Summary of our knowledge of DM

• DM properties

• DM candidates

• Direct /indirect researches

Dark Matter preliminar • constitutes about 25% of the content of the Universe. It

cannot consist of atomic matter, which makes up stars, planets and ourselves. This known form of matter accounts for at most 5% of the content of the Universe.

• The hunt for DM is multi-pronged and interdisciplinary, involving cosmology and astrophysics, particle physics, direct and indirect detection experiments and searches at particle colliders.

• Many DM candidates have been proposed, many of them associated with beyond the Standard Model (SM) physics at the electroweak scale.

Dark Matter Evidences

Dark Matter Evidences

• evidence for the existence of much more matter than what can be assigned to visible matter at all scales from dwarf galaxies to the largest cosmological scales. The excess is what is called dark matter (DM).

First Evidence: Coma Cluster

• Evidence for the existence of DM was first discovered by Fritz Zwicky in the 1930’s.

• Measurements of the velocity dispersion of galaxies in the Coma Cluster led him to the conclusion that they could not be bound to the cluster by the gravitational attraction of the visible matter (stars, gas,dust) alone.

Rotation curves at galactic scales

• The existence of DM was rediscovered in the 1970’s, this time at galactic scales, by Vera Rubin and others.

• The flat rotation curves of disk galaxies, i.e. the constant rotational speed v as function of the radius r beyond the visible disk, indicates that the mass continues to grow with the radius

• If all the mass of the galaxy M would be concentrated at the disk, an object of mass m orbiting the galaxy beyond the disk would experience a gravitational force F = GMm/r2 = mv2/r, and v = (GM/r)1/2 would decrease as r1/2. A constant v requires the mass M to grow with r. Most of the matter of galaxies resides in spheroidal “dark haloes”.

Rotation Curve of Galaxy• Dynamical studies of the Universe began in the late 1950’s.

• astronomers began to study their internal motions (rotation for disk galaxies) and their interactions with each other, as in clusters.

• The question was soon developed of whether we were observing the mass or the light in the Universe. Most of what we see in galaxies is starlight.

• the brighter the galaxy, the more stars, therefore the more massive the galaxy. By the early 1960's, there were indications that this was not always true, called the missing mass problem.

Missing matter in the Universe• The first indications that there is a significant fraction of missing

matter in the Universe was from studies of the rotation of our own Galaxy, the Milky Way. The orbital period of the Sun around the Galaxy gives us a mean mass for the amount of material inside the Sun's orbit. But, a detailed plot of the orbital speed of the Galaxy as a function of radius reveals the distribution of mass within the Galaxy.

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Keplerian rotation curveRotation following Kepler's 3rd law is shown above as planet-like or differential rotation. Notice that the orbital speeds falls off as you go to greater radii within the Galaxy. This is called a Keplerian rotation curve.

Rotation curve of the GalaxyTo determine the rotation curve of the Galaxy, stars are not used due to interstellar extinction. Instead, 21-cm maps of neutral hydrogen are used. When this is done, one finds that the rotation curve of the Galaxy stays flat out to large distances, instead of falling off as in the figure above. This means that the mass of the Galaxy increases with increasing distance from the center.

Missing matter in the UniverseThe surprising thing is there is very little visible matter beyond the Sun's orbital distance from the center of the Galaxy. So, the rotation curve of the Galaxy indicates a great deal of mass, but there is no light out there. In other words, the halo of our Galaxy is filled with a mysterious dark matter of unknown composition and type.!

Cluster Masses:

Cluster Masses:

Missing Mass• When these measurements were performed, it was

found that up to 95% of the mass in clusters is not seen, i.e. dark.

• Since the physics of the motions of galaxies is so basic (pure Newtonian physics), there is no escaping the conclusion that a majority of the matter in the Universe has not been identified, and that the matter around us that we call `normal' is special.

• The question that remains is whether dark matter is baryonic (normal) or a new substance, non-baryonic.

Mass-to-Luminosity Ratios• Exactly how much of the Universe is in the form of

dark matter is a mystery and difficult to determine, obviously because its not visible. It has to be inferred by its gravitational effects on the luminous matter in the Universe (stars and gas) and is usually expressed as the mass-to-luminosity ratio (M/L). !

• A high M/L indicates lots of dark matter, a low M/L indicates that most of the matter is in the form of baryonic matter, stars and stellar remnants plus gas.

Mass-to-Luminosity Ratios

Lensing• The same argument applied to the gas bound to clusters, as well as

weak gravitational lensing measurements of the total amount of mass in clusters, indicate that DM constitutes 6 times the mass in visible matter

Dwarf Galaxies• The smallest galaxies in our Universe are referred to as dwarf galaxies.

• They are dwarfed by galaxies like our Milky Way by their total mass, which can be as much as 10,000 times smaller than our galaxy.

• Even though they are the most abundant galaxies in the Universe, their low masses mean less stars and gas, making them faint and challenging to observe.

• One common type of dwarf galaxy known as dwarf spheriodals (or dSph) are devoid of gas, and are observed as faint clumps of stars, like the dwarf galaxy in Figure 1.

• Observations of these dwarf galaxies suggest they they are dominated by dark matter throughout the entire galaxy, even more so than more massive galaxies like our Milky Way.

Cusp vs Core• Large, cosmological simulations of galaxy formation and evolution using the LCDM model for

dark matter predict that the density of dark matter in galaxies has a “cusp“, or peak, towards the center of the galaxy. However, observations of these dSph galaxies have shown that they contain flat, central density profiles, called “cores”, rather than cusps.

• Figure, shows an example of the cusp (green) and core (black). We don’t know how these cores form, and whether or not their existence represents a big problem in our understanding of dark matter. One possibility, however, is that cuspy dark matter profiles can transform into cored profiles through gas and star formation physics that is usually not included in large, cosmological simulations.

• Use analytical and numerical models to study how the movement of baryons, gas and stars, effects the distribution of dark matter in these galaxies, and how it may transform cuspy dark matter profiles to cored profiles.

• Figure 2: The dark matter density profiles of the two dwarf galaxy models, T2 and T3, at the start of the N-body simulations (green) and after 200 million years (black). The purple lines show how the dark matter profiles evolve after 200 million years without the gas clumps. The initial distribution is cuspy, trending towards at peak at the center, while the final distribution is cored, or flat. (Source: Figure 3 of Nipoti & Binney 2015)

Cusp vs Core

Dwarf Galaxies• Dwarf galaxies are the most DM-dominated systems known.

• There are indications of the existence of a core (a region of constant density) in the DM density profile of dwarf galaxies, instead of the cusp (with density growing towards the center) predicted by CDM-only simulations.

• Both these potential problems of (collissionless) CDM may disappear once the effect of visible matter is fully taken into account, or with WDM or SIDM (Warm or Self-Interacting DM) [50, 49, 51] instead of CDM (see also [45] and references therein). With WDM too few satellite galaxies might be produced in the Milky Way, if its mass is small enough

• The only particles in the SM which are part of the DM are neutrinos. They are lighter than 1 eV and remain in thermal equilibrium in the early Universe until temperatures of a few MeV (see below), thus they are HDM. There are no CDM or WDM particle candidates in the SM but there are many in extensions of the SM. Candidates for CDM are “axions”, WIMPs, and many others. Sterile neutrinos and some non-thermal WIMPs (see below), among others, are good WDM candidates.

CMB constrains• The latest observations by the Planck collaboration of the anisotropies in

the Cosmic Microwave Background (CMB) combined with others (see Table 10 of [9]) have lead to a composition of ΩDM h2 = 0.1187 ± 0.0017 of DM, Ωbh2 = 0.02214 ± 0.00024 of ordinary matter (baryons, i.e. protons and neutrons) and ΩDE = 0.692 ± 0.010 of dark energy.

Baryonic Matter• Five independent measurements of the abundance of atomic

matter in the Universe show that it amounts to less than 5% of the content of the Universe:

1. the X-ray emission from galaxy clusters,

2. the relative height of the odd and even peaks in the angular power spectrum of CMB anisotropies,

3. the abundance of light chemical elements generated in Big Bang Nucleosynthesis (BBN),

4. Baryon Acoustic Oscillations

5. absorption lines of the light of Quasars.

What do we know about Dark Matter?

Gravitational InteractionDM has attractive gravitational interactions and is either stable or has a lifetime ≫ tU (tU =13.798 ±0.037 × 109 y)"

• We have, in fact, no evidence that DM has any other interaction but gravity. Thus, one can wonder if the many observational evidences for DM are instead showing departures from the law of gravity itself. This general idea cannot be tested unless expressed in a particular model and the most successful model of this type proposed so far has been the “Modified Newtonian Dynamics” (MOND) [14], and its covariant version, the “Tensor- Vector-Scalar” (TeVeS) gravity model . But they cannot replace DM, as described below.

MONDMOND with only visible matter is not enough at scales larger than galactic scales."

• In 1983 M. Milgrom proposed MOND as an alternative explanation for the flat rotation curves of galaxies. In MOND

F = ma becomes F = μ(a)ma, where μ(a) deviates from unity only for very small accelerations a ≪ a0, for which μ = a/a0.

• Thus the gravitational for M leads to:

F =GMm/r2 =maμ, which for larger,i.e. a≪a0, √yields a = GMa0/r.

Equating this with the centripetal acceleration a = v2/r, one gets a constant orbital speed v = (GMa0)1/4

Mond Problems• MOND is in good agreement with galaxy-scale

observations for a0 ≃ 1.2×10−10 m/s2, without any need for DM (and for this a0, the effects of MOND are too small to be measurable in laboratory or solar-system scale experiments). But it fails at larger scales, in particular in the “Bullet Cluster” , unless some form of DM is introduced

• MOND is only a non-relativistic theory, thus it cannot be used where General Relativity is needed. TeVeS is a relativistically covariant theory in which the tensor field in Einstein’s theory of gravity is replaced by scalar, vector and tensor fields, which interact in such a way to yield MOND in the weak-field non-relativistic limit.

TeVeS Failure:Bullet ClusterBaryonic !

Matter

Dark!Matter

TeVeS Failures• In the “Bullet Cluster” , discovered in 2004, the baryonic matter (hot

gas observed in X-rays) is at the center, spatially segregated from the two lateral gravitational potential wells (measured via weak gravitational lensing).

• CDM Model: The explanation of this system based on DM is that two galaxies collided, leaving behind the interacting gas, while the DM of both galaxies passed through (which yields an upper limit on the self interaction of the DM).

• TeVeS Model requires 2-3 times more matter than accounted for by the visible matter alone. TeVeS advocates propose the existence of some “cluster baryonic dark matter” (CBDM), for example. But once some kind of extra matter is necessary, it then becomes an issue of taste which type of DM one considers more likely.

DM do not interact with light• DM is not observed to interact with light."

• This means that most of the DM must have a small enough electromagnetic coupling or be very heavy. Upper limits are derived from background light at all frequencies

• The DM could be neutral, maybe with a small electric or magnetic dipole moment .

• It could have a small effective electric charge, such as that of “Milli-Charged DM”. Charged DM particles can also act as nearly collisionless if their mass is sufficiently large. “Millicharged DM” can be part of a “dark sector” which couples to SM particles only though the admixture of a “dark photon” of a “dark U’(1)” gauge symmetry with the usual photon (or the Z boson).

• It could be “Atomic DM”, with dark protons and dark electrons forming dark atoms, or “Mirror DM” whose Lagrangian is a copy of that of the SM, but for the mirror particles. These are some possibilities in which the dark or “secluded” sector has some of the richness of the visible sector, with hidden gauge interactions and flavor

• Observational upper limits on the cross section of elastic DM -photon interactions can be surprisingly large, e.g. a recent limit from simulations of Milky Way sub-haloes is σelastic ≤ 4 × 10−33 cm2 (m/GeV) . DM−γ An important consequence of the small interaction of DM with light is that the DM cannot cool by radiating photons during galaxy formation.

Mostly dissipationless• The bulk of the DM must be dissipationless, but part of it could be dissipative."

• “Dissipationless” mean that the DM cannot cool by radiating as baryons do to collapse in the center of disk galaxies. Otherwise, their extended dark halos would not exist.

• Galaxies start as structures made of the primordial admixture of dark and visible matter. Then, visible matter dissipates energy by emitting photons and falls into the potential well of the object. Because this emission is isotropic, the visible matter preserves any angular momentum it might initially have. Thus as it collapses to the center, it increases its angular speed until it becomes unstable towards the formation of a disk, which thus rotates much faster than the dark halo.

• While most of the DM must be nearly dissipationless, a small fraction of it could be dissipative. Part of the matter in the galaxy, the visible matter, is dissipative and its presence does not disrupt the stability of dark haloes. Thus a similar fraction, 5-10%, of the DM could also be dissipative and even form a “Dark Disk”. This is the idea behind “Partially Interacting DM” (PIDM) and “Double Disk DM” (DDDM). The dissipative DM component could emit “dark photons” or other “dark” particles.

• A Dark Disk was shown to arise in some simulations of galaxy formation including baryonic matter besides the usual non-dissipative Cold DM, but with dissipative DM it should be a pervasive feature of all disk galaxies.

MACHOS• The mass m of the major component of the DM has only been constrained within

some 80 orders of magnitude.

• There is a firm upper bound m ≤ 2×10−9 M⊙ = 2×1048 GeV at the 95% CL. It comes from unsuccessful searches for MACHOS (“Massive Astrophysical Compact Halo Objects”) in the dark halo of our galaxy using gravitational microlensing with the Kepler satellite, and from the ground-based MACHO and EROS surveys, combined with bounds on the granularity of the DM for masses larger than 30 M⊙.

• Microlensing is a type of gravitational lensing in which the multiple images of the lensed star are superposed, producing a magnification of the star flux if an object passes near the line of sight to the star as it moves through the dark halo. Above this limit, MACHOS can account for only a small fraction of the dark halo of our galaxy.

• Among the best candidates for MACHOS are “Primordial Black Holes” (PBH). These are hypothetical black holes that could be created in a primordial phase transition, maybe during inflation.

MACHOS CONSTRAINS• However, several limits apply to PBH which do not apply to other MACHOS and

constrain the fraction of DM in PBH to be < 1 for almost any mPBH mass. PBH lighter than 1015g would have decayed by Hawking radiation. Not having observed this radiation in γ-rays excludes mPHB

COLLISIONLESS• DM has been mostly assumed to be collisionless, however the upper limit on DM

self-interactions is very large. The best limits on self-interactions are derived from the “Bullet Cluster”(where the DM of the two colliding galaxies had to pass through each other) and the non-sphericity of the halos of galaxies and galaxy clusters. The upper limit is huge:

σself/m ≤ 1cm2/g ≃ 2 barn/GeV ≃ 2×10−24

cm2/GeV.

• Explaining the existence of DM cores in dwarf galaxies may constitute a problem for the usual collisionless Cold DM models. Collisions of the DM particles with themselves would erase small scale structure and turn cuspy central density profiles into cored profiles in dwarf galaxies, if the cross section is close to the mentioned upper limit.

• DM with this large self-interaction is called “Self-Interacting DM” (SIDM). DM with less than an order of magnitude smaller σself is indistinguishable from collissionless.

• With SIDM the reduced central densities of dwarf galaxies imply reduced velocity dispersions, which can alleviate the “too big to fail problem” of collisionless CDM (see below). There are many particle models for SIDM, most with complicated “dark sectors”

COLD OR WARM, BUT NOT HOT….

• The bulk of the DM is Cold or Warm, thus particle DM requires physics beyond the SM."

• The DM is classified as hot, cold or warm according to how relativistic it is when galactic-size perturbations enter into the horizon (i.e. when these perturbations become encompassed by the growing horizon ≃ ct). This happens when T ≃ keV. Hot DM (HDM) is relativistic, Cold DM (CMD) is non-relativistic and Warm DM (WDM) is becoming non-relativistic at this moment.!

• The presence of DM in the early Universe is necessary for the formation of structure in the Universe. Structures in baryons cannot grow until recombination, when atoms become stable. Before then the photon pressure in the plasma prevents it. But at recombination baryons must fall into already formed potential wells of DM, or there would not be enough time to form the structures we observe now. Thus, it is the DM which determines the major features of the large-scale structure of the Universe.Perturbations in the DM survive at horizon crossing only if the DM is non-relativistic. !

• With HDM, primordial galaxy-size density inhomogeneities would not survive, superclusters would form first and later galaxies through fragmentation. This does not reproduce the observed Universe. !

• With CDM, inhomogeneities much smaller than galaxy size survive, thus galaxies and clusters incorporate many smaller structures which form first. Some of them are not entirely tidally destroyed, thus, a large number of substructure is expected within CDM dark haloes. With WDM the smaller structures formed first are of the size of dwarf galaxy cores, thus there is much less substructure within large haloes than with CDM.

• Either CDM or WDM can account for all the large scale structure observations. The difference between them is at the dwarf-galaxy scale, where observations and their interpretation are still not conclusive.

too big to fail• with only CDM (assumed to be collisionless) find

within a halo similar to that of the Milky Way, of the order of 10 subhaloes so massive and dense that they seem “too big to fail” to form lots of stars within them and be visible. But the Milky Way and Andromeda do not seem to have satellite galaxies with stars moving as fast as would be expected in these dense sub-haloes. This constitute the so called “too big to fail” problem of CDM

DM candidates are relics from the pre-BBN era

• Most DM candidates are relics from the pre-BBN era, from which we have no data."

• The computation of the relic abundance and primordial velocity distribution of particle DM candidates produced before the BBN temperature limit of 4 MeV depends on assumptions made regard-ing the thermal history of the Universe. With different viable cosmological assumptions, the relic density and velocity distribution of the DM candidates may change considerably

• We usually characterize DM particle candidates according to how they are produced as “thermal” or “non-thermal” relics.

• “Thermal” relics are produced via interactions with the thermal bath, reach equilibrium with the bath and then “decouple” or “freeze-out” when their interactions cannot keep up with the expansion of the Universe. Chemical equilibrium is achieved when reactions that change the number of particles are faster than the expansion rate of the Universe H (or the reaction time is shorter than the lifetime of the Universe ≃ H−1). After chemical decoupling or freeze-out the number of particles per comoving volume remains constant. After kinetic decoupling, the exchange of momentum with the radiation bath ceases to be effective.

• “Non-thermal” DM particles are all those not produced in this way. For example, they could be produced via the decay of other particles, which themselves may or may not have a thermal abundance.

Dark Matter Candidates: Take one

Baryonic Dark Matter:• The abundance of light elements that there is also a problem in our understanding of the fraction of the

mass of the Universe that is in normal matter or baryons.

• The fraction of light elements (hydrogen, helium, lithium, boron) indicates that the density of the Universe in baryons is only 2 to 4% what we measure as the observed density.!

• Can dark matter be some form of normal matter that is cold and does not radiate any energy? For example, dead stars?!

• Once a normal star has used up its hydrogen fuel, it usually ends its life as a white dwarf star, slowly cooling to become a black dwarf. However, the timescale to cool to a black dwarf is thousands of times longer than the age of the Universe. !

• High mass stars will explode and their cores will form neutron stars or black holes. However, this is rare and we would need 90% of all stars to go supernova to explain all of the dark matter.!

• Another avenue of thought is to consider low mass objects. Stars that are very low in mass fail to produce their own light by thermonuclear fusion. Thus, many, many brown dwarf stars could make up the dark matter population. Or, even smaller, numerous Jupiter-sized planets, or even plain rocks, would be completely dark outside the illumination of a star. The problem here is that to make-up the mass of all the dark matter requires huge numbers of brown dwarfs, and even more Jupiter's or rocks. We do not find many of these objects nearby, so to presume they exist in the dark matter halos is unsupported.

Barionic DM candidate

Non Baryonic DM candidates

• An alternative idea is to consider forms of dark matter not composed of quarks or leptons, rather made from some exotic material.

• If the neutrino has mass, then it would make a good dark matter candidate since it interacts weakly with matter and, therefore, is very hard to detect. However, neutrinos formed in the early Universe would also have mass, and that mass would have a predictable effect on the cluster of galaxies, which is not seen.!

• Another suggestion is that some new particle exists similar to the neutrino, but more massive and, therefore, more rare. This Weakly Interacting Massive Particle (WIMP) would escape detection in our modern particle accelerators, but no other evidence of its existence has been found.

• The more bizarre proposed solutions to the dark matter problem require the use of little understood relics or defects from the early Universe. One school of thought believes that topological defects may have appears during the phase transition at the end of the GUT era. These defects would have had a string-like form and, thus, are called cosmic strings. Cosmic strings would contain the trapped remnants of the earlier dense phase of the Universe. Being high density, they would also be high in mass but are only detectable by their gravitational radiation.

• Lastly, the dark matter problem may be an illusion. Rather than missing matter, gravity may operate differently on scales the size of galaxies. This would cause us to overestimate the amount of mass, when it is the weaker gravity to blame. This is no evidence of modified gravity in our laboratory experiments to date.

Non Baryonic DM candidates

Current View of Dark Matter:• The current observations and estimates of dark

matter is that 20% of dark matter is probably in the form of massive neutrinos, even though that mass is uncertain.

• Another 5 to 10% is in the form of stellar remnants and low mass, brown dwarfs.

• However, the combination of both these mixtures only makes about 30% the amount mass necessary to close the Universe.

Current View of Dark Matter:

Dark Matter Candidates Take 2

Weakly-interacting massive particles (WIMPs):

• Introduced by Steigman & Turner.

• This key features of this particle class are exactly as described: interactions around or near typical weak-force interactions (the fine-structure constant α near the weak-scale coupling ∼ 10−2), particle masses near the weak scale ( m∼100 GeV in particle-physics units, similar to the mass of a silver atom.)

• Candidates in the WIMP class include the supersymmetric neutralino (the lowest-mass eigenstate of the supersymmetric partners of neutral Standard Model gauge bosons) and the Kaluza-Klein photon. Both of these candidates emerge out of theories to introduce new physics at the electroweak breaking scale (the minimal supersymmetric standard model [MSSM] and universal extra dimensions [UED]), and possibly to explain why that scale is so much lower than the Planck scale.

WIMPS Miracle• The origin of the WIMP miracle is this. If WIMPs are in a thermal

bath in the early Universe with other particles, having been born out of decays of the inflaton or something of the like, then we can solve Boltzmann equations to find that WIMPs “freeze out” (i.e., stop being created/destroyed through annihilations with other particles) at a comoving density that is inversely proportional to the WIMP annihilation cross section σann.

• Unless decays are important, this comoving number density is fixed for all future time. By dimensional analysis (recalling that mass is inversely proportional to the length scale in particle-physics units), the annihilation cross section should be σann∝α2/m2. If you put this dimensional-analysis cross section into early-Universe Boltzmann equations, the comoving number density of WIMPs matches the number density inferred from cosmological observations,

Axions• they emerge out of a solution to the strong-CP problem in

particle physics.

• Axions are in some ways less natural than WIMPs because it is tricky to get their comoving number density to match the observed dark-matter density.

• There are a number of axion production mechanisms (all of which must be present to some extent), but the preferred way to produce dark- matter axions is through non-thermal coherent oscillations of the axion field near the QCD phase transition.

• In that case, axions are light (∼10μeV) and are born with no momentum.

Gravitinos:• The gravitino, the supersymmetric partner of the graviton.

• Depending on exactly how supersymmetry is broken, the gravitino could be anywhere in the mass range of∼eV to TeV, although masses keV are disfavored because they wash out too much small-scale structure.

• In order for lighter gravitinos to be dark matter, one typically must introduce some non-standard cosmology. If the next-lightest supersymmetric particle (NLSP) is only barely more massive than the gravitino, that particle species may be thermally produced and then decay at a later time to gravitinos. Thus, even though gravitinos basically do not interact with the Standard Model (and thus would not typically be born as thermal relics), they can inherit the WIMP miracle from the NLSP.

• The gravitino in this scenario is a “superWIMP”. Because these massive gravitinos are born out of decays at relatively high momentum, they can smear out primordial density perturbations on small scales. Gravitinos are not nearly as beloved as WIMPs as dark-matter candidates because of the difficulty of getting the abundance just right and because they are much harder to detect using conventional methods

Sterile neutrinos:• Sterile neutrinos are neutrinos that do not interact electroweakly. Since

mass eigenstates are not the same as the electroweak eigenstates (i.e.,νe,νμ,ντ), sterile neutrinos may mix with electroweak, or active, neutrinos. Sterile neutrinos have been proposed in a number of contexts; they can be a mass-generating mechanism for the active neutrinos, they can simply be the right-handed counterparts to the active species, or explain certain neutrino-experiment anomalies. As dark matter, sterile neutrinos may be created in the early Universe in a variety of ways.

• Depending on their creation mechanism, they can be consortianed by their effects on smaller-scale structure in the Universe. Because sterile neutrinos mix with active neutrinos, they have a small decay probability to an active neutrino and a photon. The simplest model of sterile neutrino dark matter (Dodelson-Widrow neutrinos) are excluded by a combination of small-scale structure observations and non-detections of X-rays from galaxies.

DM DETECCION

• DM scattering off the nuclei

• DM annihilations in the galaxy

• Produce DM at high energy at the colliders like LHC

Rare interactions