Lecture 3 WIMPs as dark matter WIMPs with a new mediating force - PowerPoint PPT Presentation

Lecture 3 � � WIMPs as dark matter � � WIMPs with a new mediating force � � Dark photon as a mediator of a dark force � � Chasing anomalies with light new particles: galactic positrons, muon g-2, charge radius problem, etc � � Strategies to search for dark photons, with light dark matter and without. A few results. � ��

WIMP paradigm, some highlights WIMP-nucleus H mediated - scattering DM-SM mediators DM states SM states Cosmological (also galactic) annihilation Collider WIMP pair-production ! ann v ! 1pbn " c 1. What is inside this green box? I.e. what forces mediate WIMP-SM interaction? � 2. Do sizable annihilation cross section always imply sizable scattering rate and collider DM production? �

Progress in direct detection of WIMPs � Z mediated exchange - hmmmmmu sec- scat- scat- get of 0 get www.M/tggs mediated nu- masses mobelg be- of Fig. 8 Parameter space for elastic spin-independent dark matter- ��

Summary of main features of WIMPs � � Regulates its abundance via self-annihilation with σ v ~ 10 -36 cm 2 � � The mass of WIMPs is in a several GeV – several TeV window (Lee- Weinberg) if the interaction is mediated by weak-scale forces. � - � Direct detection experiments surpass sensitivity of 10 -45 cm 2 without seeing a signal – worrying sign for many models, including models with Z boson mediators. Probes the tree-level Higgs exchange � - � Sensitivity of direct detection will be ultimately limited by elastic recoil of solar and atmospheric neutrinos � � Low mass WIMPs do not carry much energy, and are less constrained � ��

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What changes if we add a mediator? � scale the lower We mass can of DM FYIMGEM .im . Weinberg ⇒ Manual Lee : I |536qyNow Smalley of Mmedoakor is , Wimp lighter than much mw , allowed Dark matter is . ��

“Simplified model” for dark sector (Okun’, Holdom, … ) µ ν + 1 L = L ψ ,A + L χ ,A � − � 2 m 2 µ ) 2 . 2 F µ ν F � A � ( A � . L ψ ,A = − 1 µ ν + ¯ 4 F 2 ψ [ γ µ ( i ∂ µ − eA µ ) − m ψ ] ψ L χ ,A � = − 1 µ ν ) 2 + ¯ 4( F � χ [ γ µ ( i ∂ µ − g � A � µ ) − m χ ] χ , e A – photon, A’ – “dark photon”, γ ψ - an electron, χ - a DM state, � g’ – a “dark” charge γ � χ � “Effective” charge of the “dark sector” particle χ is Q = e × ε (if momentum scale q > m V ). At q < m V one can say that χ � 6 � m − 2 radius, r 2 V . particle χ has a non-vanishing EM charge radius , � � . � � Dark photon can “communicate” interaction between SM and �� dark matter. It represents a simple example of BSM physics. �

A reasonable top down model? � nkfmri ⇒ ngn q =g←aaeptoags € particles heavy magnet my xlog(agg) loops particles of heavy 152 .( deputy E can give = loops ) member the of on . ��

Two types of WIMPs Un-secluded Secluded . E~ / Ultimately discoverable Potentially well-hidden Size of mixing*coupling is set by Mixing angle can be annihilation. Cannot be too small. 10 -10 or so. It is not fixed by DM annihilation You think gravitino DM is depressing, but so can be WIMPs 6 ��

Consequences of light mediator � ) Sommerfeld ( aka enhancement Coulomb . Atiiiiiii - < 2mg ma ' ' A ; . * x←y±⇐⇐± - - - - at DM nomrelatovishe For heavy vEm)G←d=2t¥×(am•% C , at that Notice freeze out - the galaxy inside and V 0.3C ; - v~lo→c c9Igff÷ canoe >>1 ��� . . .

Consequences of light mediator � � Galactic positron excess can be modelled via the annihilation of DM into light mediators. � Need the enhancement of cross section at low galactic velocities ��� � Increasingly under pressure from the absence of the excesss in γ�

Astrophysical motivations for very MeV-scale DM: 511 keV line � FIG. 4 511 keV line map derived from 5 years of INTE- 26 Al γ -ray emission after 9-year FIG. 7 Map of Galactic GRAL/SPI data (from Weidenspointner et al. , 2008a). observations with COMPTEL/CGRO (from Pl¨ uschke et al. , 2001). There is a lot more positrons coming from the Galactic Center and the bulge that expected. The emission seems to be diffuse. 1. Positrons transported into GC by B-fields? 2. Positrons are created by episodic violent events near central BH? 3. Positrons being produced by DM? Either annihilation or decay? ���

Search for dark photons, Snowmass study, 2013 A' ⇧ Standard Model A' ⇧ Standard Model 10 � 2 10 � 2 “bumps in m ll ” a ⇤ , 5 ⌅ WASA KLOE a ⇤ , 5 ⌅ 10 � 3 WASA KLOE a ⇤ , ⌃ 2 ⌅ favored BaBar E774 APEX ⇤ MAMI stress Test Runs a e a ⇤ , ⌃ 2 ⌅ favored 10 � 4 E141 MAMI 10 � 3 Orsay BaBar APEX ⇤ MAMI E774 10 � 5 U70 Test Runs a e 10 � 6 CHARM DarkLight MESA APEX ⇥ ⇥ 10 � 4 VEPP � 3 10 � 7 E141 E137 LSND 10 � 8 Orsay HPS 10 � 9 10 � 5 SN 10 � 10 U70 10 � 11 10 � 3 10 � 2 10 � 1 1 10 � 3 10 � 2 10 � 1 1 m A ' � GeV ⇥ m A ' � GeV ⇥ Dark photon models with mass under 1 GeV, and mixing angles ~ 10 -3 represent a “window of opportunity” for the high-intensity experiments, not least because of the tantalizing positive ~ ( α / π ) ε 2 correction to the ��� muon g - 2 .

Theoretical status of muon g-2, SM The history of theoretical calculations goes very far in the past. Back to Schwinger’s result, a µ 1-loop QED = α / (2 π ) Currently, the QED, Strong and Weak contributions are under control a µ SM theory = 116591828±49 × 10 -11 ← reindeer a µ experiment = 116592089(63) × 10 -11 a µ Deficit = (26.1±8) × 10 -10 'K My Me # - tete ? Even larger than EW contribution ! ��� o a EW = (154 ± 2) · 10 − 11 , � µ

Latest results: A1, Babar, NA48 Signature: “bump” at invariant mass of e + e - pairs = m A’ � � 2 ' WASA KLOE ee % $ # KLOE ee ee $ & Babar: e + e - � γ V � γ l + l - � preliminary ) ! 3 ( ) 2 e " A1(+ APEX): Z e - � Z e - V g -5 ( = 10 � Z e - e + e - � HADES APEX (g " 2) + µ A1 NA48: π 0 � γ V � γ e + e - � -6 10 BaBar NA48/2 preliminary E774 -7 E141 10 -2 -1 10 10 2 m , GeV/c A’ Latest results by NA48 exclude the remainder of parameter space relevant for g-2 discrepancy. � Only more contrived options for muon g-2 explanation remain, e.g. L µ – L τ , or dark photons decaying to light dark matter. ���