Searching for dark photon. Haipeng An Caltech Seminar at USTC

Searching for dark photon Haipeng An Caltech Seminar at USTC 1

The standard model is very successful! 2

The big challenge! We just discovered a massless spin-2 particle.! We don t know how to write down a quantum field theory for it yet.! The leading solution is string theory.! The ultimate form of various string theories is believed to be the M theory, which is the central topic of ICTS. 3

But when we look up into the sky! The rotation curves of galaxies Observed Predicted assuming only the visible disk 4

But when we look up into the sky! Either Newtonian gravity (as well as general relativity) needs to be modified or there is more stuff (dark matter) we cannot see. Bullet cluster Visible stuffs are displaced from the centers of gravitational potential. Strong support of dark matter! 5

Other evidences for dark matter 6

What do we know about dark matter?! Dark (cannot block light)! Relic abundance ~ 1/4! Cold (non-relativistic)! Gravitates (like ordinary matter) 7

What do we know about dark matter?! Dark (cannot block light)! Relic abundance ~ 1/4! Cold (non-relativistic)! Gravitates (like ordinary matter)! Do we know its mass? No! Interactions with us other than gravity? No idea! Self interaction? Maybe! What is the origin of dark matter? Maybe thermal relic 8

How to answer these questions? Direct detection Production χ? χ Indirect detection SM SM 9

Dark matter direct detection 10

Dark matter indirect detection PAMELA Fermi DAMPE (悟空) AMS02 11

Dark matter production 12

Any signals from dark matter?! Direct detection " DAMA, CoGeNT (both excluded by larger experiments, CDEX)! Collider searches " Nothing yet! Indirect detections? " PAMELA positron access later confirmed by Fermi and AMS02! (Might be purely from secondary scattering ) " Fermi GeV access from the Galactic center! (Might be from point-like sources ) 13

Dark matter indirect detection 0810.4995, Nature 2009 PRL 110, 141102, 2013 14

Long range dark force! One possible origin: dark matter annihilation at the galactic center Arkani-Hamed, Finkbeiner, Slatyer, Weiner 0810.0713 Pospelov, Ritz 0810.1502 h vi GC 10 23 cm 3 sec 1! If dark matter relic abundance is from thermal annihilation, h vi Th 3 10 26 cm 3 sec 1! A boost factor is needed. S B O(100) 15

Long range dark force! What is the difference? " At GC, v ~ 10-3 c; " During dark matter freeze-out, v ~ 0.3 c. 16

Long range dark force! What is the difference? " At GC, v ~ 10-3 c; " During dark matter freeze-out, v ~ 0.3 c.! A long range attractive force can enhance the annihilation rate at low velocity (Sommerfeld enhancement). Arkani-Hamed, Finkbeiner, Slatyer, Weiner 0810.0713 Pospelov, Ritz 0810.1502 17

Small scale structure anomalies! Too big to fail problem Klypin et al APJ 1999 & Moore et al APJ 524 " Cold dark matter simulation predicts much more Galactic dwarf satellites than observed.! Core/Cusp problem " Cold dark matter simulation predicts the dark matter distribution has a cusp at the center of dwarf galaxies. " What observed is a core. Flores, Primack APJ 1994 & Moore, Nature 1994 18

Small scale structure anomalies! People are still debating on if the traditional Lambda CDM model with baryonic feedback can solve these problems or not. Hopkins et al 1602.05957 19

Small scale structure anomalies! People are still debating on if the traditional Lambda CDM model with baryonic feedback can solve these problems or not. Hopkins et al 1602.05957! Self interacting dark matter might be the solution to the problem. Spergel, Steinhardt PRL 2000, Tulin, Yu, Zurek PRD 2013, Kaplinghat, Tulin, Yu PRL 2016 20

The dark photon model! Lagrangian L = 1 4 V µ V µ + 1 2 m2 V V µ V µ 1 2 applev µ F µ V µ : dark photon vector boson V µ = @ µ V @ V µ : dark photon field strength tensor m V : mass of dark photon apple : kinetic mixing betweenphoton and dark photon F µ : photon field strength tensor 22

The dark photon model! Lagrangian L = 1 4 V µ V µ + 1 2 m2 V V µ V µ 1 2 applev µ F µ! m V > 1 MeV V! e + e The dark photon decays fast and can be the mediator of the dark force. 24

The dark photon model! Lagrangian L = 1 4 V µ V µ + 1 2 m2 V V µ V µ 1 2 applev µ F µ!! m V > 1 MeV V! e + e The dark photon decays fast and can be the mediator of the dark force. m V < 1 MeV V! 3 Landau-Yang theorem V / apple2 4 m 9 V m 8 e The dark photon can easily be cosmologically stable, and play the roll of dark matter. 25

Outline of the talk! Phenomenology of dark photon as a dark matter candidate m V < 1 MeV " Dark photon from the Sun " Dark photon dark matter! Phenomenology of dark photon as dark force mediator m V > 1 MeV " Collider searches for dark bound states " Dark matter annihilation via bound state formation 26

m V < 1 MeV! People were using CAST experiment and light-shiningthrough-the-wall experiment to detect light dark photon Sun V CAST Shielding Light-shining-through-the-wall Vacuum chamber X-ray Detector 27

m V < 1 MeV Solar Solar life time Redondo (JCAP 2008) Direct searches 28

Solar dark photon Solar Solar life time Redondo (JCAP 2008) New solar dark radiation constraint HA, M.Pospelov, J.Pradler 1302.3884&PLB 29

Solar dark photon! Comparison between photon and dark photon " Photon: massless, two transverse modes " Dark photon: massive, two transverse modes one longitudinal mode. 30

Solar dark photon! Matrix element

Solar dark photon! Matrix element E.O.M

Solar dark photon! Matrix element E.O.M Feynman gauge:

Solar dark photon! Matrix element E.O.M Feynman gauge: Plasma effect

Solar dark photon! Inside a thermal plasma (with NR electrons) " For transverse modes m V! 0

Solar dark photon! Inside a thermal plasma (with NR electrons) " For transverse modes m V! 0 " For longitudinal mode m V! 0

Solar dark photon! Inside the Sun, because of the plasma effect " " Longitudinal flux dominates for m V << E. " The previous calculation of the longitudinal flux was completely wrong. T / (m V /E) 4 L / (m V /E) 2 HA, M.Pospelov, J.Pradler 1302.3884&PLB 39

Solar dark photon! Why CAST is not sensitive? " In the vacuum, photon only has transverse modes " In materials, photon develops longitudinal mode. Sun V CAST Shielding! The detector should contain a large volume of materials ------ the dark matter detector Vacuum chamber X-ray Detector 40

Solar dark photon! Resonant production Transverse resonance Longitudinal resonance

Solar dark photon! Longitudinal resonant production!! p, 1 ev <! p < 300 ev The detector should be able to detect ~ 100 ev energy deposition. 300 ev HA, M.Pospelov, J.Pradler 1309.6599 42

Solar dark photon! We are looking at electron recoils.! Up to now only XENON10 collaboration has published the result in this energy region. V PM T Xenon gas PM T X A ( * ) photons PM T e - E E PM T 1 ev. E r. 300 ev Xenon liquid Xenon atom PM T PM T PM T PM T 43

Solar dark photon Constraint from solar dark radiation HA, M.Pospelov, J.Pradler 1302.3884&PLB HA, M.Pospelov, J.Pradler 1304.3461&PRL 44

Dark photon dark matter! Coherent oscillation 1 2 m2 V V 2! The longitudinal mode of dark photon can be produced during inflation, and keep oscillating till today to be a dark matter candidate. Graham, Mardon, Rajendran 1504.02102 45

Dark photon dark matter! Nonrelativistic v 10 3! m V! Can be detected by XENON if m V > 12 ev. PM T Xenon gas PM T photons PM T E PM T V X A ( * ) e - E Xenon liquid Xenon atom PM T PM T PM T PM T 46

Dark photon dark matter HA, M.Pospelov, J.Pradler, A.Ritz 1412.8378 HA, M.Pospelov, J.Pradler, A.Ritz, K.Ni 1510.04530 47

Summary for m V < 1 MeV! We have shown how to detect the solar dark photon and dark matter dark photon with XENON10.! In principle all the dark matter detectors can used to search for dark photon, it is very important to understand the electron recoil background.! A lot of new proposals are on the way. 48

m V > 1 MeV! Dark photon decays into charged particles " Beam damp experiments " Bump searches " Electron and muon g-2 " Meson decays " Electroweak precision test " Supernova 49

m V > 1 MeV K ±! ± 0, 0!! Dark photon decays into charged particles V, V! e + e source target X Mixing with Z boson wall detector e + e! V, V! e + e,µ + µ 50

m V > 1 MeV! Dark photon decays into charged particles Very little information from dark matter! 51

Searching for dark bound states! Searching for dark photon as the dark force mediator " How to know it carries the dark force? " If the dark force is strong enough, dark bound states can be produced at the colliders. " We propose to use high luminosity B-factories to search for dark bound states. HA, Echenard, Pespelov, Zhang 1510.05020 & PRL 52

Searching for dark bound states 0.01 Hg - 2L e HA, Echenard, Pespelov, Zhang 1510.05020 & PRL NA48 ê 2 Hg - 2L m Dark photonûbabar 0.001 E744 Hcurrent limit, a D =0.25L k 10-4 10-5 E141 Orsay Hcurrent limit, a D =0.5L Hfuture limit, a D =0.25L Hfuture limit, a D =0.5L U70 h D and U D ûbabar future B factory no bound states 10-6 CHARM 0.005 0.01 0.02 0.05 0.1 0.2 0.5 1. 2 m V HGeVL 53

Bound state effects on dark matter indirect detection! The Sommerfeld enhancement Arkani-Hamed, Finkbeiner, Slatyer, Weiner 0810.0713 Pospelov, Ritz 0810.1502! If the dark photon is light enough, dark bound state can form by emitting a dark photon. 54

Bound state effects on dark matter indirect detection! In the limit m V! 0 " Sommerfeld enhancement v = 2 D m 2 D 2 D v " Kramer s formula v = 128 3 D 3 p 3m 2 D v log D v 55

Bound state effects on dark matter indirect detection! In the limit m V! 0 v Kramer v Sommerfeld 4 log D v Z de E = X n 1 2 2 µ/n 3 log 2 log + 1 2 µv2 v v 2 µ n 2 56

Bound state effects on dark matter indirect detection! In the limit m V! 0 v Kramer v Sommerfeld 4 log D v " For gamma rays from the galactic center v ~ 10-3 c " The logarithmic factor is from the infrared divergence. " Famous people sometimes also miss the leading contribution. 57

Bound state effects on dark matter indirect detection 100. 50. CMB a D >0.3 md HTeVL 10. 5. 1. 0.5 Inconsistent with LUX, SN&BBN Focus of this study Bound states cannot form today or during recombination Bound states do not exist 0.1 0.001 0.01 0.1 1 10 100 1000 HGeVL m V 58

Bound state effects on dark matter indirect detection s HGeV -2 L 0.1 0.01 0.001 10-4 10-5 5 10 20 50 100 m V HGeVL HA, Wise, Zhang 1604.01776 59

Bound state effects on dark matter indirect detection! Constraints from the Galactic center gamma rays HA, Wise, Zhang 1604.01776 60

Future works for dark bound states! Collider searches " Other high luminosity colliders (SeaQuest, HPS )! Cosmic rays " Gamma rays from dwarf galaxy " Anti-proton constraint from the AMS02 " Dark matter annihilate inside the Sun & the earth " Sensitivity of DAMPE (future) 61

Summary! Dark photon model is a well motivated model for dark matter self-interaction and dark matter itself.! There is still a lot of work to do. Thank you for your attention! 62