The first parallel session of the day. I missed the start of the first talk taking care of some money worries.
2:00 pm: Energy Peak: back to the cosmic gamma ray excess, Jong-Chul Park
Seems to be interested in the 130 GeV and 3.5 keV lines. No wait, about the GCE, just mentioned that for self-promotional purposes.
Model-independent constraints here (?) disfavouring DM coupling to first two generation fermions as possible explanation. Comes from AMS-02 antiproton data. Do they include uncertainties in DM structure?
Some kind of relation to particle physics. Details are not your enemy. Okay, not a connection to particle physics but to kinematics. All of this seems to be finally coming around to using consecutive two-body decays to get a peaked spectrum. In particular need some light pseudoscalar that decays to two photons.
2:25 pm: Morphology of the Soft X-Ray Excess in Galaxy Clusters from a Cosmic ALP Background, Stephen Angus
The soft X-ray excess: almost 20 years old, discovered by EUVE in 1996. Energies ~ 0.4 keV in Virgo & Coma clusters. Confirmed by ROSAT to be found at 38 clusters. Not well-probed by current experiments, because small field of view. Seen up to z ~ 0.3, but only away from galactic plane and far from cluster centre.
Two main astrophysical explanations: thermal bremmstrahlung from warm gas; or IC off of CMB for a non-thermal electron population. For former, expect warm gas to cool much faster than cluster lifetime; also expect thermal emission lines which are not observed. For latter, expect synchrotron emission; also problem that emission extends well outside of core of cluster; are there any photons there? Both ideas have problems but cannot be excluded at this time.
Consider dark radiation. From string theory perspective, expect ~ 100 moduli with associated ALPs. Any non-zero branching ratio for moduli decay to hidden states wil populate DR; in this sense, harder to explain its absence than its presence. Of course, data is consistent with no DR and only allows a small amount.
ALPs produced this way are the "Cosmic ALP Background", CAB. In addition to CMB tests, can look for ALP-photon conversion or ALP decay (e.g. 3.5 keV line). Intention here is to use ALP-γ conversion to explain the X-ray excess. Need axion mass small compared to plasma frequency, 10-12 eV.
2:50 pm: Measuring the TeV Cosmic Ray Electron Flux with CREST, Michael Schubnell
This is CREST, not CRESST, which confused me a little at first.
Very high energy electrons, above measurements from e.g. PAMELA or AMS-02. Indeed, highest previous energies from HESS. Part of the problem is that the electron flux is very low at such high energies, plus an overwhelming proton background. It is worthwhile as it can yield information on the spatial distributions of CR sources. Electrons lose energies like p2, so only close sources (<1 kpc) can contribute. We know of a few but there might be more.
Search looks for synchrotron radiation from electrons in Earth's magnetic field. Using secondaries gives you a large effective area, and since protons don't emit (much) synchroton radiation you have an efficient rejection of that background.
Experiment ran for 10 day flight over antarctic summer. Recovered in good condition but have not flown again. Didn't manage to get as high (low pressure) as hoped; also solar flare backgrounds higher than expected.
Ended up a path-finding rather than scientific mission, which unfortunately did not get further funding.
3:25 pm: Axion Research at CAPP/IBS, Sung Woo Youn
Similarity between Higgs mechanism and axion mechanism: both involve spontaneous breaking of a symmetry. Thus Higgs discovery helps strengthen interest in the axion model.
Use reverse Primakov effect: axion conversion to photons in the presence of a magnetic field. Do this in a resonant cavity. Typical conversion power ~ 10-22 W!!
Hard efforts to increase signal by getting better experimental parameters (bigger cavities, stronger magnetic fields, etc.)
2:00 pm: Energy Peak: back to the cosmic gamma ray excess, Jong-Chul Park
Seems to be interested in the 130 GeV and 3.5 keV lines. No wait, about the GCE, just mentioned that for self-promotional purposes.
Model-independent constraints here (?) disfavouring DM coupling to first two generation fermions as possible explanation. Comes from AMS-02 antiproton data. Do they include uncertainties in DM structure?
Some kind of relation to particle physics. Details are not your enemy. Okay, not a connection to particle physics but to kinematics. All of this seems to be finally coming around to using consecutive two-body decays to get a peaked spectrum. In particular need some light pseudoscalar that decays to two photons.
2:25 pm: Morphology of the Soft X-Ray Excess in Galaxy Clusters from a Cosmic ALP Background, Stephen Angus
The soft X-ray excess: almost 20 years old, discovered by EUVE in 1996. Energies ~ 0.4 keV in Virgo & Coma clusters. Confirmed by ROSAT to be found at 38 clusters. Not well-probed by current experiments, because small field of view. Seen up to z ~ 0.3, but only away from galactic plane and far from cluster centre.
Two main astrophysical explanations: thermal bremmstrahlung from warm gas; or IC off of CMB for a non-thermal electron population. For former, expect warm gas to cool much faster than cluster lifetime; also expect thermal emission lines which are not observed. For latter, expect synchrotron emission; also problem that emission extends well outside of core of cluster; are there any photons there? Both ideas have problems but cannot be excluded at this time.
Consider dark radiation. From string theory perspective, expect ~ 100 moduli with associated ALPs. Any non-zero branching ratio for moduli decay to hidden states wil populate DR; in this sense, harder to explain its absence than its presence. Of course, data is consistent with no DR and only allows a small amount.
ALPs produced this way are the "Cosmic ALP Background", CAB. In addition to CMB tests, can look for ALP-photon conversion or ALP decay (e.g. 3.5 keV line). Intention here is to use ALP-γ conversion to explain the X-ray excess. Need axion mass small compared to plasma frequency, 10-12 eV.
2:50 pm: Measuring the TeV Cosmic Ray Electron Flux with CREST, Michael Schubnell
This is CREST, not CRESST, which confused me a little at first.
Very high energy electrons, above measurements from e.g. PAMELA or AMS-02. Indeed, highest previous energies from HESS. Part of the problem is that the electron flux is very low at such high energies, plus an overwhelming proton background. It is worthwhile as it can yield information on the spatial distributions of CR sources. Electrons lose energies like p2, so only close sources (<1 kpc) can contribute. We know of a few but there might be more.
Search looks for synchrotron radiation from electrons in Earth's magnetic field. Using secondaries gives you a large effective area, and since protons don't emit (much) synchroton radiation you have an efficient rejection of that background.
Experiment ran for 10 day flight over antarctic summer. Recovered in good condition but have not flown again. Didn't manage to get as high (low pressure) as hoped; also solar flare backgrounds higher than expected.
Ended up a path-finding rather than scientific mission, which unfortunately did not get further funding.
3:25 pm: Axion Research at CAPP/IBS, Sung Woo Youn
Similarity between Higgs mechanism and axion mechanism: both involve spontaneous breaking of a symmetry. Thus Higgs discovery helps strengthen interest in the axion model.
Use reverse Primakov effect: axion conversion to photons in the presence of a magnetic field. Do this in a resonant cavity. Typical conversion power ~ 10-22 W!!
Hard efforts to increase signal by getting better experimental parameters (bigger cavities, stronger magnetic fields, etc.)
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