Cosmic e excess and its possible origins and implications

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Cosmic e/- excess and its possible origins and
implications

• Bi Xiao-Jun
• IHEP, CAS
• 2009-6-15

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Results of PAMELA, ATIC, Fermi and HESS
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PAMELA results Nature 458, 607 (2009) (citation
240)Observation of an anomalous positron
abundance in the cosmic radiation
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(No Transcript)
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ATIC bump at the electron/positron spectrum
Chang et al. Nature456, 362 2008
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Fermi results

• Fermi gives softer spectrum of (ee-) than ATIC.
  Excess exists above the conventional model

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HESS result

• HESS measures the Cherenkov light of the showers
  developed by high energy cosmic rays in the
  atmosphere.
• It can discriminate hardronic and EM showers.
  However, can not discriminate electrons and
  gammas.
• Electron flux is larger than gamma beyond the
  galactic plane.
• Energy resolution is at best 15.

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Summary of data

• PAMELA observed substantive positron excess
  beyond the standard prediction by cosmic ray
  physics above 10 GeV up to 80 GeV, which is
  consistent with previous results from HEAT and
  AMS01.
• Both ATIC and Fermi observed excesses at the
  electronpositron spectrum however, they are not
  consistent with each other
• ATIC data show very sharp falling at the
  electron spectrum at 600 GeV. It is consistent
  with the spectrum produced by dark matter Fermi
  shows softer spectrum which may be due to
  astrophysical sources
• Assuming the conventional background from cosmic
  rays, in addition primary sources that generate
  equal amount of electron/positron, ATIC and Fermi
  are consistent with PAMELA separately, that each
  set of data can be explained by the same
  source(s) simultaneously.
• No antiproton excess. The sources seem have to be
  leptonic.

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Explanations by astrophysical origins
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Recalculation of background

• New formulization of spallation cross section pp
  -gt e
• Uncertainty from e- spectrum
• Uncertainty from propagation

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PAMELA result might not be really an excess but
due to the uncertainty of background estimate
Delahaye et al., 0809.5268
But cannot explain ATIC result
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Possible origins of ee- pp interaction (Blasi,
0903.2794) Occur at the cosmic ray
acceleration source hard spectrum
Comment nature for Fermi spectrum antiprotons
may set constraints on this picture
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From CRs interaction
Hu,Yuan,Wang,Fan,Zhang,Bi, 0901.1520

• There is knee in CR spectrum at 1015 eV
• It is proposed the knee is generated by
  interaction, with E?1eV, the threshold energy is
  at 1015 eV
• 3 converted can explain the ATIC or
  Fermi Fermi excess

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Nearby pulsars
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Astrophysical sources
D. Hooper et al. S. Profumo

• Nearby pulsars

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Explanations by dark matter
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Primary positron/electrons from dark matter
implication from new data

• DM annihilation/decay produce leptons mainly in
  order not to produce too much antiprotons.
• Very hard electron spectrum -gt dark matter
  annihilates/decay into leptons.
• Very large annihilation cross section, much
  larger (1000) than the requirement by relic
  density. ( 1) nonthermal production, 2)
  Sommerfeld enhancement, 3) Breit-Wigner
  enhancement, 4) dark matter decay.)

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why should annihilate into leptons?
Yin, et al. arXiv0811.0176
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Dark matter models to produce leptons

• Kinematically suppression
• Mass of fis about 1GeV, is
• Kinematically suppressed to antiprotons
• At the same time attractive interaction can
  enhance the annihilaition rate, Sommerfeld
  enhancement. (Arkani-Hamed et al. 0810.0713  )
• Dynamically suppression, f carries U(1)e-µ(t)
  (Baek Fox Bi)
• DM models related with neutrino masses (Bi et al
  0901.0176 Cao et al. 0901.1334 )
• These models lead to hard positron spectrum and
  suppress antiproton flux naturally.

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Large flux

• Nonthermal production
• (from N. Weiner)
• Sommerfeld enhancement
• For attractive Coulomb Potential
• To enhance the dark matter annihilation we have
  long range attractive force

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Large flux
Ibe, Murayama, Yanagida Guo, Wu Bi, He, Yuan

• Breit-Wigner enhancement,

Bi, He, Yuan 0903.0122
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Decay dark matter with life time 1026s
Yin, Yuan, Liu, Zhang, Bi, Zhu, Zhang Chen,
Nojiri et al Ibarra, Tran Hamguchi, Shirai,
Yanagida
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ATIC and Fermi

• Model of gauged U(1)e-µ(t)
• 1TeV DM to emu, etau can explain ATIC
• 1.5 TeV DM to mutau can explain Fermi data
• All have similar annihilation rate

Bi, He, Yuan 0903.0122
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Models independent constraint on the nature of
dark matter by the PAMELA and ATIC data---
branching ratios to gauge bosons and quarks are
constrained
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Propagation of CRs

• Due to rapid energy loss of electron/positron the
  flux measured on Earth comes from nearby regions
  antiproton can come from far regions
• Height of diffusion region is a crucial factor
  astrophysical sources from the Galactic plane is
  less affected however, DM signals will be
  affected significantly.

From Lavalla
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Give good fits to PAMELA and ATIC results with WW
quark branchs
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Upper bounds on the WW and quark branching ratios
for MDM1TeV
Bi, Li, Gu, Zhang, Zhang
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Constraints on some DM models (1TeV)

• Neutralino, mainly into gauge bosons excluded
• In UED KK mode of U(1)Y gauge boson, 30 into
  quarks (universal KK mass) marginally allowed
• U(1)B-L, 40 into quarks, slightly disfavored
• Leptophilic models U(1)e-mu(tau), best fit
  data

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How to discriminate different scenarios?
Radiations from these primary
electrons/positrons to account for PAMELA and
ATIC data
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Different models can work well

• Adjusting parameters, DM decay/annihilation,
  pulsars can all explain PAMELA and ATIC

Zhang, Bi, Liu, Liu, Yin, Yuan, Zhu, 0812.0522 
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Source distribution
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Can we test these scenarios?

• Detect the synchrotron and IC gamma ray signals
  from the GC.

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Diffuse gamma spectra
Fermi LAT
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Discrimination I. precise spectrum measurement of
ee-
Dark matter vs. pulsar sharp drop or not? (Hall
Hooper, 0811.3362)
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Discrimination I. precise electron spectrum
(continued)
Dark matter vs. pulsar fluctuations on the
spectrum? (Malyshev et al., 0903.1310)
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Discrimination II. anisotropy of electron flux
Diffuse vs. point (Hooper et al., 2009, JCAP,
01, 025)
A local dark matter clump may also behave like
this.
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Constraints on the dark matter scenarios
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Emission from the GC
Bi et al., 0905.1253

• Constraint on the central density of DM
• Tension
• Exist for the
• annihilating
• DM scenario

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Constraints on the minimal subhalos by
observations of clusters
A. Pinzke et al., 0905.1948

• Standard CDM predicts the minimal subhalos
• Observation constrains
• Fermi limit to
• DM is warm

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Constraints from extragalactic diffuse gamma rays

S. Profumo et al., 0906.0001
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Constraints from CMB

• DM annihilation heats and ionizes the
  photon-baryon plasma at z1000, constrained by
  WMAP and Planck

T.R. Slatyer et al., 0906.1197
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Outlook

• PAMELA finally detect positron to 270GeV
  antiproton to 190 GeV (published lt100GeV)
• PAMELA detect ee- to 2 TeV (not released)
• AMS02 launch at 2010
• Re-flight of ATIC for electrons (AREL) was
  proposed to NASA Mar. 2009
• Satellite detector for electron up to 10TeV
  proposed in China
• LHC and DD help to determine nature of dark matter