Indirect dark matter detection: recent results and perspectives - PowerPoint PPT Presentation

Indirect dark matter detection: recent results and perspectives Piero Ullio � SISSA & INFN ( T rieste ) “Frontiers of Fundamental Physics 14”, Marseille, July 15, 2014

Outline: A review focussed on the weakly interacting massive particles ( WIMPs ) as dark matter candidates: • Short introduction on the dark matter problem to put the WIMP prejudice in perspective. • The WIMP paradigm facing the null detection so far of physics beyond � the Standard Model at the LHC: indirect ( or direct ) detection as � guideline? • Recent experimental/theoretical highlights on WIMP indirect detection; any clean signal and/or clean signature? • In case clean signatures are not available, the complementarities among � di ff erent messengers and targets may be the key to solve the dark matter � puzzle; combining di ff erent information however is non - trivial: an � exercise to illustrate this point. Disclaimer: a review making no attempt to produce an exhaustive list of references on all recent results

Dark matter indirectly ( gravitationally ) detected! Plenty of evidence for non - baryonic cold ( or coldish - as opposed to hot ) DM being the building block of all structures in the Universe. E.g.: ( Planck, 2013 ) it accounts for the Angular scale gravitational potential 90 � 18 � 1 � 0.2 � 0.1 � 0.07 � 6000 wells in which CMB 5000 acoustic oscillations 4000 take place: D � [ µ K 2 ] 3000 2000 1000 0 2 10 50 500 1000 1500 2000 2500 . Hu website Multipole moment, � Credit: W Relying on the assumption that GR is the theory of gravity; still, it is very problematic to explain, e.g., the prominence of the third peak in an alternative theory of gravity and matter consisting of baryons only

Connection to a particle dark matter framework? The standard model for cosmology, the Λ CDM model, does not aim to address questions regarding the nature of the DM component: the DM term is treated as a classical, cold, pressure - less fluid subject to gravitational interactions only ( no coupling to ordinary matter or photons, no self - coupling ) ; tests of such gravitational coupling determine with accuracy its mean density: ( Planck, 2013 + WMAP 7 yr pol. ) Ω DM = 0 . 1199 ± 0 . 0027 and the spectrum of its perturbations ( nearly scale invariant, as expected from inflation ) . Reformulating the DM problem in terms of elementary particles in the dilute limit ( two - body interactions dominating over multi - body interactions ) is an assumption, and not the only possible extrapolation, e.g.: the recent attention on primordial black holes as DM; the recent interest on the possibility that DM is the form of ( or, in certain regimes behaves like ) a condensate. Will it be possible to single out this possibilities?

Observations and particle properties of DM Assuming a particle formulation, astro/cosmo observables provide mainly informations on the properties that DM does not have, e.g.: it needs to be non - baryonic, non - relativistic at the phase of matter - radiation equality, … This is enough to say that DM is NOT within the SM of particle physics. At the same time, loose bounds on the properties which are crucial for devising a detection strategy for DM particles - the mass and coupling to ordinary matter. The mass scale is essentially unconstraint, admitting ultralight bosons � 10 − 22 eV ( with macroscopic de Broglie wavelength ) , fermions at the level of about ( Gunn - T remaine bound from phase space density limits ) , and 50 eV no relevant upper limits ( up to the MACHO range tested via lensing searches and even beyond ) The interaction scale has very tight limits with photons ( DM millicharge, electric and magnetic dipole moments severely suppressed ) , significant with baryons, rather weak for self - interactions ( from galaxy clusters morphologies and mergers, such as from the Bullet cluster - early claims of evidence for self interaction from the Musket Ball cluster not confirmed )

Observations and particle properties of DM Assuming a particle formulation, astro/cosmo observables provide mainly informations on the properties that DM does not have, e.g.: it needs to be non - baryonic, non - relativistic at the phase of matter - radiation equality, … This is enough to say that DM is NOT within the SM of particle physics. At the same time, loose bounds on the properties which are crucial for devising a detection strategy for DM particles - the mass and coupling to ordinary matter. i- Particle models cover a large part of the available range of masses and Kim& Carosi, 2010 interactions: sub - eV axions, keV of and sterile neutrinos, GeV - TeV WIMPs, supermassive DM close to the Planck scale; gravitinos with gravitational interactions, numerous weakly interacting DM candidates, mirror s, photons DM with strong self - interactions, …

Guidelines to narrow the DM problem? Focussing corresponds almost always to ratify a prejudice. Possible criteria to support such option include: • A clean production mechanism, e.g.: thermal production ( symmetric, asymmetric ) , non - thermal states ( e.g. from heavier state decays ) , production as a condensate, gravitational production, … � • A motivation from an open problem in the SM of particle physics, e.g.: the naturalness problem, the violation of CP in strong interactions, a mechanism to explain neutrino masses, … � • An impact on observables in cosmology or astrophysics, in connection, e.g., to the possibly discrepancies of the SM with observations on small scales ( non - linear regime; galactic and sub - galactic scales; central over densities and abundance of substructures ) , e.g.: W arm DM, self - interacting DM, DM carrying macroscopic quantum e ff ects, DM with with non - standard couplings with photons or baryons. Numerical N - body simulations are starting to touch these cases; still to be cleared is the role of baryons in DM numerical simulations. �

Guidelines to narrow the DM problem? • An “aesthetic” motivation in analogy to other counterparts, e.g.: Asymmetric DM relying on a mechanism explaining the reason why the density of baryons and DM are comparable. � • A “pragmatic” motivation: lacking incontrovertible evidence for new physics at accelerators, DM may be the only window for new physics. � • A “contingent” motivation: given some “anomaly” ( e.g. an excess in the radiation detected towards the GC ) you study the class of compatible candidates ( mass, interaction, annihilation or decay mode ) without ( necessarily ) a reference particle framework. � • A systematic evaluation of what is experimentally accessible � “Historical” DM candidates - ( SUSY ) WIMPs, axions, sterile neutrinos, … - have mainly been motivated as relying on a natural production mechanism and, at the same time, carrying a particle physics motivation; should one give up on such approach?

CDM particles as thermal relics Thermal equilibrium of enforced via: χ Γ ( T f ) = n eq χ ( T f ) � σ A v � T = T f � H ( T f ) 0.01 Ω χ h 2 � M χ s 0 Y eq χ ( T f ) 0.001 0.0001 ρ c /h 2 Y χ ≡ n χ ( freeze - out + entropy conservation ) s � M χ s 0 H ( T f ) ρ c /h 2 s ( T f ) � σ A v � T f ( standard rad. dominated cosmology ) g � 1 · 10 − 27 cm − 3 s − 1 � M χ χ T f g e ff � σ A v � T = T f with: M χ /T f ∼ 20 1 10 100 1000 Ω χ h 2 ' 3 · 10 − 27 cm − 3 s − 1 WIMP “miracle” h σ A v i T = T f The WIMP recipe to embed a dark matter candidate in a SM extension: foresee an extra particle that is stable ( or with lifetime exceeding the age χ of the Universe ) , massive ( non - relativistic at freeze - out ) and weakly interacting. Plenty of frameworks in which it is viable to apply this recipe.

WIMP coupling to ordinary matter: Early Universe ≈ halo annihilations tests at LHC ! ! q q CP _ _ _ _ q q ! ! direct annihilation production detection ! ! crossing � crossing � symmetry symmetry A model independent approach to WIMP q q detection? scattering

Back to WIMP coupling to ordinary matter: Early Universe ??? ≈ halo annihilations tests at LHC ??? ! ! p SM CP ??? ___ _ _ p ! ! SM direct annihilation production detection ! ! crossing � crossing � ??? symmetry ??? symmetry ??? Details in the model may become critical for q q “light” detection strategy scattering

LHC BSM null detection and the WIMP framework The viewpoint that new states close to the EW scale are needed to address the hierarchy problem, a pillar of beyond - SM searches, is severely shaking. The viability of a WIMP DM is significantly reshaped but not ruled out. � E.g.: among the viable option for MSSM neutralino DM prior the LHC: 1. light Bino ( SU ( 2 ) singlet ) annihilating into fermions via t - & u - channel exchange of moderately light sfermion ( bulk region of the CMSSM ) ; � 2. annihilation on a s - channel Higgs resonance; � 3. coannihilation with a sfermion quasi degenerate in mass; � 4. well - tempering of Bino - Higgsino fraction; � Direct detection target 5. pure Higgsino ( SU ( 2 ) doublet ) of 1.1 TeV mass or pure Wino ( SU ( 2 ) triplet ) of 2.5 TeV mass. Indirect detection target only 1. has been wiped out by the LHC ( but was already in trouble because of flavour observables and Higgs mass limits ) ; 2. has been reshaped by the ( SM ) Higgs discovery; 3., 4. & 5. have not ( or marginally ) addressed.