Axion Dark Matter

5 Dec 2016, 09:00 → 9 Dec 2016, 18:00 Europe/Stockholm

FB42 and FB53 (Nordita, Stockholm)

Ariel Goobar, Frank Wilczek, Katie Freese, Lars Bergström, Sebastian Baum, Yannis Semertzidis

Venue

Nordita, Stockholm, Sweden

Scope

The recent years have brought exciting developments in axion physics and breakthroughs in the experimental searches seem very likely at this time. To review the current status and foreseeable experimental advances, this workshop will bring together leading researchers from around the world who are exploring the physics around axions using a variety of techniques, to share their insights and find synergies.

Timetable

[Registration - deadline October 30]

The number of attendees for this conference is limited to 50.

More information will be available here later.

Monday, 5 December

08:30 → 09:45 Registration

09:45 → 10:00 Welcome

Speakers: Hans Thors Hansson (NORDITA), Prof. Lars Bergström (The Oskar Klein Centre, Fysikum, SU)

10:00 → 11:00 Introduction to Axion Physics

The explanation of approximate time reversal symmetry, based on deep general principles, is one of the great triumphs of modern physics. It has an annoying gap, however. The most convincing ideas to repair the gap lead us to predict the existence of a new kind of particle, the axion, with remarkable properties. If axions exist, it is likely that they make a substantial contribution to the dark matter of the universe. Experiments to detect axions are challenging, but ambitious efforts are underway. The equations of axions also emerge (with different parameters) as the effective description of interesting condensed matter systems, and in that context have inspired some beautiful experiments.

Speaker: Prof. Frank Wilczek (Massachusetts Institute of Technology & Stockholm University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-wilczek.pdf

11:00 → 11:15 Coffee break

11:15 → 12:15 Axion Dark Matter

The axion is arguably one of the best motivated candidates for dark matter. For a decay constant above about 10^9 GeV, axions are dominantly produced non-thermally in the early universe and hence are “cold”, their velocity dispersion being small enough to fit to large scale structure. Moreover, such a large decay constant ensures the stability of axion dark matter at cosmological time scales and its behaviour as a collisionless fluid at cosmological length scales. In this introductory review, we present the state of the art of axion dark matter predictions.

Speaker: Andreas Ringwald (DESY)

slides http://www.nordita.org/docs/agenda/slides-axions2016-ringwald-1.pdf

12:15 → 13:15 Lunch

13:15 → 14:15 The Search for Axions

OKC COLLOQUIUM The axion is a hypothetical particle proposed, almost 40 years ago, to explain why the strong interactions are P and CP invariant. Additional motivation for its existence is due to the fact that a cold population of axions is naturally produced in the early universe. These cold axions may constitute the dark matter today. I'll briefly review the limits on the axion from particle physics, stellar evolution and cosmology. The various constraints suggest that the axion mass is in the micro-eV to milli-eV range. In this range, its interactions are so weak that the axion was once thought invisible. Nonetheless a number of methods have been proposed to search for so-called "invisible" axions. I'll describe these techniques, the experiments that have implemented them, and the results that have been obtained so far.

Speaker: Prof. Pierre Sikivie (University of Florida)

slides www.nordita.org/docs/agenda/slides-axions2016-sikivie-1.pdf

14:15 → 14:45 Coffee break

14:45 → 15:45 Axions in the Skies

Axions and axion-like particles (ALPs) are abundantly produced in stars. The backreaction on stellar evolution, ranging from ordinary stars to core-collapse supernovae, provides powerful astrophysical constraints. The Sun is the source for the CAST and future IAXO axion searches. Moreover, within allowed parameters, ALPs can strongly modify the propagation of TeV gamma rays. The status of these traditional topics is reviewed with an emphasis on possible future developments.

Speaker: Prof. Georg Raffelt (MPI Munich)

slides http://www.nordita.org/docs/agenda/slides-axions2016-raffelt.pdf

15:45 → 16:00 Coffee break

16:00 → 17:00 Status of WIMP searches

Arguably, the WIMP paradigm needs to be disposed of before the bulk of the community would move to searches for axions. In my contribution I will give an overview of status and near future of WIMP searches, including indirect WIMP detection, direct WIMP detection, some words on LHC and a brief comparison of approaches.

Speaker: Jan Conrad (SU Fysikum)

slides http://www.nordita.org/docs/agenda/slides-axions2016-conrad.pdf

17:00 → 17:30 Discussion

19:30 → 21:30 Conference dinner

Tuesday, 6 December

09:30 → 10:00 Microwave Axion Experiment in Korea

The axion is an excellent dark matter candidate motivated by the Peccei-Quinn solution to the strong-CP problem. The IBS Center for Axion and Precision Physics Research (CAPP) in Korea will explore the dark matter axion using a method suggested by P. Sikivie, converting axions into microwave photons in a resonant cavity permeated by a strong magnetic field. CAPP's first microwave axion experiment, CULTASK (CAPP's Ultra Low Temperature Axion Search in Korea) is being launched at KAIST (Korea Advanced Institute of Science and Technology) campus, utilizing top of the line equipment and technology. I will outline many R&D efforts that are currently being undertaken to make the axion search range broader and the sensitivity greater. I will also discuss the results from the recent engineering runs and future plans of the axion experiment.

Speaker: Dr Chung Woohyun (CAPP/IBS)

slides http://www.nordita.org/docs/agenda/slides-axions2016-chung.pdf

10:00 → 10:30 Status of the ADMX RF-cavity axion search

The Axion Dark-Matter Experiment is currently the most sensitive detector of dark-matter QCD axions in the more plausible range of axion masses and couplings. This detector recently began taking data. This is a status report on ADMX data-taking operations and plans.

Speaker: Prof. Leslie Rosenberg (University of Washington)

slides http://www.nordita.org/docs/agenda/slides-axions2016-rosenberg.pdf

10:30 → 11:00 ABRACADABRA: A Broadband Search for Axion-Like Dark Matter

Adding an axion to the SM has the potential to solve two open mysteries of modern physics: the particle nature of dark matter and the strong CP problem. Present searches for axion-like dark matter have typically been resonant-cavity scans focused on the axion mass range $\gtrsim10^{-6}$ eV. We are proposing a new cryogenic-based broadband approach, combining a high-field toroidal magnet and a SQUID read-out system, that allows us to probe much lighter axion masses without a resonant cavity. Our setup is called ABRACADABRA. At MIT, we are building a small proof-of-concept setup with a $\sim12$\,cm diameter toroidal magnet producing a proposed magnetic field of $\sim1$\,T. This will be mounted in our in-house dilution refrigerator and collect data for a few months with a broadband readout circuit. With this readout, we will probe previously unexplored parameter regions of axion-like dark matter. At this point, we will have the option of switching to a resonant readout circuit to perform a resonant search. This first setup will be sensitive to axion masses in the range $10^{-13} \lesssim m_a \lesssim 10^{-8}\,\mathrm{eV}$ down to $g_{a\gamma\gamma}\sim10^{-13}\,\mathrm{GeV}^{-1}$ --- depending on noise sources. In this talk, we discuss the general setup, the expected systematics and projected sensitivity.

Speaker: Dr Jonathan Ouellet (Massachusetts Institute of Technology)

slides http://www.nordita.org/docs/agenda/slides-axions2016-ouellet.pdf

11:00 → 11:30 Coffee break

11:30 → 12:00 The axion from Hell

I describe axion dark matter in the post-inflationary scenario where one can get a prediction for the axion mass in the simplest cosmological scenarios. I describe experimental possibilities to discover it and a new proposal: the dielectric haloscope.

Speaker: Javier Redondo (Zaragoza University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-redondo-1.pdf

12:00 → 12:30 SM*A*S*H - A minimal model for particle physics and cosmology

A minimal extension of the Standard Model (SM) providing a complete and consistent picture of particle physics and cosmology up to the Planck scale is presented. We add to the SM three right-handed SM-singlet neutrinos, a new vector-like color triplet fermion and a complex SM singlet scalar ? whose vacuum expectation value at ?1011 GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously. Primordial inflaton is produced by a combination of ? and the SM Higgs. Baryogenesis proceeds via thermal leptogenesis. At low energies, the model reduces to the SM, augmented by seesaw-generated neutrino masses, plus the axion, which solves the strong CP problem and accounts for the dark matter in the Universe. The model can be probed decisively by the next generation of cosmic microwave background and axion dark matter experiments.

Speaker: Andreas Ringwald (DESY)

slides http://www.nordita.org/docs/agenda/slides-axions2016-ringwald-2.pdf

12:30 → 13:00 Effective Lagrangian for pseudo-scalar mesons and axion

We extend the effective Lagrangian for pseudo-scalar mesons that includes the effect of the axial anomaly, gives a satisfactory spectrum of pseudo-scalar mesons and allows one to compute the $\theta$ dependence of hadronic processes, to include the axion. We use it to show that the $\theta$ dependence disappears and we compute various properties of the axion. In particular, we show that the mass of the axion is given, in the chiral limit, by the Weinberg-Wilczek formula in terms of the quark masses with the addition of a term containing the topological susceptibility of Yang-Mills theory. This additional factor is irrelevant at zero temperature but could become important at finite temperature.

Speaker: Paolo Di Vecchia (Nordita)

slides http://www.nordita.org/docs/agenda/slides-axions2016-divecchia.pdf

13:00 → 14:00 Lunch

14:00 → 14:30 Bose-Einstein Condensation of Dark Matter Axions

It has long been accepted that axions produced by vacuum realignment, and related prccesses, during the QCD phase transition form a cold degenerate Bose gas and are a candidate for the dark matter. More recently it was found that dark matter axions thermalize through their gravitational self-interactions and form a Bose-Einstein condensate (BEC). On time scales long compared to their rethermalization time scale, almost all the axions go to the lowest energy state available to them. In this behaviour they differ from the other dark matter candidates. Axions accreting onto a galactic halo fall in with net overall rotation because they almost all go to their lowest energy available state for given total angular momentum. In contrast, the other proposed forms of dark matter accrete onto galactic halos with an irrotational velocity field. The inner caustics are different in the two cases. I'll argue that the dark matter is axions, at least in part, because there is observational evidence for the type of inner caustic produced by axion BEC.

Speaker: Pierre Sikivie

slides http://www.nordita.org/docs/agenda/slides-axions2016-sikivie-2.pdf

14:30 → 15:00 Axion cold dark matter and miniclusters in modified cosmological models

The properties of cold dark matter axions strongly depend on the thermal history of the Universe prior BBN. I show that axion cold dark matter may be a good probe of the pre-BBN epoch since observational properties like the axion mass, its velocity dispersion, and the mass&size of axion miniclusters can be used to distinguish among different scenarios.

Speaker: Dr Luca Visinelli (Stockholm University, Oskar Klein Centre)

slides http://www.nordita.org/docs/agenda/slides-axions2016-visinelli.pdf

15:00 → 15:30 Simulations of ultralight axion dark matter halos

Ultra-light axions (ULAs) are dark matter candidates which suppress the growth of perturbations on scales below their de Broglie wavelength and predict solitonic halo cores owing to their "quantum pressure" support. They therefore give rise to new phenomenology in large-scale structure formation and galaxy evolution. The nonlinear, non-relativistic dynamics of ULA halos can be numerically modeled by solving the Schroedinger-Poisson equations or, equivalently, the fluid equations with an additional quantum pressure term. Several approaches to simulate structure formation with ULA dark matter, both directly and semi-analytically, as well as a new stochastic model for the core-halo mass relation will be presented.

Speaker: Prof. Jens Niemeyer (Goettingen University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-niemeyer.pdf

15:30 → 16:00 Coffee break

16:00 → 16:30 The ALPS II project at DESY and prospects for future light-shining-through-a-wall experiments

Weakly interacting slim particles (WISPs) are searched for in purely laboratory based experiments with the so-called light-shining-through-a-wall (LSW) approach. Here the detection of axion and axion-like particles, which seem to be the best motivated WISPs from theoretical considerations, requires the presence of a long and strong magnetic field perpendicular to the light path. At DESY, the ALPS II experiment will combine dedicated complex optics, largely based on experiences gained in the context of LIGO, new detector technologies and modified dipoles from the decommissioned HERA proton accelerator. ALPS II aims for taking data in 2019. In the future the sensitivity of LSW experiments could be greatly enhanced by making use of advanced high field magnets presently under development in the frame of HE-LHC and FCC.

Speaker: Dr Axel Lindner (DESY)

slides http://www.nordita.org/docs/agenda/slides-axions2016-lindner-1.pdf

16:30 → 17:00 Coherent generation and detection of axions in laser experiments.

Light shining through walls experiments allow the use of a coherent detection scheme which takes advantage of the well defined energy of the generated relativistic axion. I will discuss the heterodyne detection scheme and its integration into the ALPS experiment.

Speaker: Dr Guido Mueller (University of Florida)

slides http://www.nordita.org/docs/agenda/slides-axions2016-mueller.pdf

17:00 → 17:30 Axion-like particle search with NA62

Fixed target experiments are a particularly useful tool in the search of very weakly coupled particles in the MeV-GeV range: The NA62 experiment at CERN, which is currently taking data, provides an excellent opportunity to search for a plethora of beyond-the Standard Model particles. I will outline the status and prospects of these efforts, detailing on the example of Axion-like Particles.

Speaker: Ms Babette Dobrich (CERN)

slides http://www.nordita.org/docs/agenda/slides-axions2016-doebrich.pdf

17:30 → 18:00 Discussion

Wednesday, 7 December

09:00 → 09:30 Multiple-cavity detectors for axion search

Exploring higher frequency regions in axion dark matter searches using microwave cavity detectors requires a smaller size of the cavity as the TM010 frequency scales inversely with the cavity radius. One of the intuitive ways to make a maximal use of a given magnet volume, and thereby to increase the experimental sensitivity, is to bundle multiple cavities together and combine their individual outputs ensuring phase-matching of the coherent axion signal. The Experiment of Axion Search aT CAPP (EAST-C) is a dedicated project to develop multiple-cavity systems at the Centre for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS). The conceptual design of the phase-matching mechanism and experimental feasibility using a quadruple-cavity system will be presented in this talk.

Speaker: Dr SungWoo Youn (CAPP/IBS)

slides http://www.nordita.org/docs/agenda/slides-axions2016-youn.pdf

09:30 → 10:00 First results from a microwave cavity axion search at 24 micro-eV

I will report on the first results from a new search for axion dark matter using a microwave cavity detector at ~5 GHz frequencies. This detector has achieved near-quantum-limited sensitivity using a dilution refrigerator and a Josephson parametric amplifier, and excluded axion-photon-photon couplings a factor of 2.3 above the benchmark KSVZ model in the mass range 23.55 micro-eV< m <24.0 micro-eV. These are the first limits within the QCD axion model band in the mass decade above 10 micro-eV.

Speaker: Benjamin Brubaker (Yale University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-brubaker.pdf

10:00 → 10:30 Upgrade of WISPDMX and Preliminary Result

The microwave cavity experiment WISPDMX is the first direct WISP (Weakly Interactive slim particles) dark matter search experiment probing the particle masses in the 0.8-2.0 *eV range. The first stage of WISPDMX measurements has been completed at nominal resonant frequencies of the cavity, upgrading of the data acquisition and analyzing has been done to increase the sensitivity of the experiment, with further enhancement from the second plunger. We report preliminary result from the cavity tuning at the second stage of WISPDMX, and preparation for the high resolution run.

Speaker: Mr Le Hoang Nguyen (University of Hamburg)

slides http://www.nordita.org/docs/agenda/slides-axions2016-nguyen.pdf

10:30 → 11:00 Coffee break

11:00 → 11:30 Axion haloscopes with toroidal geometry at CAPP/IBS

The present state of the art axion haloscope employs a cylindrical resonant cavity in a solenoidal field. The Center for Axion and Precision Physics research (CAPP) of the Institute for Basic Science (IBS) in Korea, is pursuing halo axion discovery using this cylindrical geometry. Besides the cylindrical geometry, we are also taking an alternative approach of searching for halo axion with toroidal geometry which offers several advantages. A concept of toroidal axion haloscopes and present ongoing research activities and plans are to be presented.

Speaker: Byeong Rok Ko (CAPP/IBS)

slides http://www.nordita.org/docs/agenda/slides-axions2016-ko.pdf

11:30 → 12:00 proton EDM activities and muon g-2 at CAPP/IBS

The precise measurement of the muon anomalous magnetic moment is very important to check the possibilities of physics beyond the Standard Model. The new muon g-2 experiment at FNAL aims to measure the muon anomalous magnetic moment with four times better precision than previous experiment at BNL and plans to start the experiment next year, 2017. The Storage Ring proton EDM experiment has New Physics sensitivity in the range of 103 - 104 TeV. Using techniques similar to the classical muon g-2 experiment we can probe the proton EDM with high sensitivity. This is due to high intensity polarized proton beams readily available as well as the long spin coherence lifetime possible in all-electric rings. There are a few important technical issues for each experiment that we are addressing, such as CBO and muon losses for muon g-2 experiment, magnetic shielding and polarimeter for proton EDM. The principle, experiment techniques and CAPP/IBS contributions for both experiments will be presented.

Speaker: Dr Young-Im Kim (Institute for Basic Science)

slides http://www.nordita.org/docs/agenda/slides-axions2016-kim.pdf

12:00 → 12:30 Collaboration opportunities at the CAPP/IBS of Korea

The Center for Axion and Precision Physics Research (CAPP) in Korea is using a comprehensive approach towards reaching a solution in the Strong CP-problem. The largest component includes launching several axion dark matter experiments covering a wide axion mass between 1 to 100 micro-eV with the aim to either discover or refute the axion in that range even if they constitute only 10% of the local dark matter density. CAPP is developing a lab infra-structure capable of running several axion dark matter experiments simultaneously, offering opportunities for international collaborations to more efficiently cover the entire, most promising, axion mass range.

Speaker: Yannis Semertzidis (Center for Axion and Precision Physics (CAPP/IBS))

slides http://www.nordita.org/docs/agenda/slides-axions2016-semertzidis.pdf

12:30 → 13:30 Lunch

13:30 → 14:00 Vector dark matter annihilation with internal bremsstrahlung

We consider scenarios in which the annihilation of self-conjugate spin-1 dark matter to a Standard Model fermion-antifermion final state is chirality suppressed, but where this suppression can be lifted by the emission of an additional photon via internal bremsstrahlung. We find that this scenario can only arise if the initial dark matter state is polarized, which can occur in the context of self-interacting dark matter. In particular, this is possible if the dark matter pair forms a bound state that decays to its ground state before the constituents annihilate. We will show that the shape of the resulting photon spectrum is the same as for self-conjugate spin-0 and spin-1/2 dark matter, but the normalization is less heavily suppressed in the limit of heavy mediators.

Speaker: Mr Garurav Kumar Tomar (Physical Research Laboratory, Ahmedabad)

slides http://www.nordita.org/docs/agenda/slides-axions2016-tomar.pdf

14:00 → 14:30 Search for streaming dark matter axions or other exotica.

We suggest a new approach to search for galactic axions or any other particles. In addition, specific time windows, some of which are predictable and others not, could be utilised. We also suggest how to adopt the detection scheme of ongoing or planned dark matter axion searches. The required intervention will be explained. Actually no additional equipment is needed. Instead, more interdisciplinary expertise can strengthen the discovery potential of this proposal.

Speaker: Prof. Konstantin Zioutas (University of Patras)

slides http://www.nordita.org/docs/agenda/slides-axions2016-zioutas.pdf

14:30 → 15:00 Probing pseudo-Nambu-Goldstone bosons via multi-wavelengths four-wave mixing

I will discuss a strategy to search for pseudo-Nambu-Goldstone bosons coupling to two photons from sub-eV to 10 keV range.

Speaker: Prof. Kensuke Homma (Hiroshima University / IZEST, Ecole Polytechnique)

slides http://www.nordita.org/docs/agenda/slides-axions2016-homma.pdf

15:00 → 15:30 Coffee break

15:30 → 16:00 Searches for Axionlike Particles with the Fermi Large Area Telescope

Axionlike particles (ALPs) are dark-matter candidates that occur in a variety of extensions of the Standard Model. Signatures of these particles could be detected at gamma-ray energies with the Fermi Large Area Telescope (LAT) due to the coupling of ALPs to photons in external electromagnetic fields. To date, Fermi-LAT observations provide the strongest constraints on the photon-ALP coupling for ALP masses between 0.5 and 20 neV. Here, we summarize these constraints and present the sensitivity to detect an ALP induced gamma-ray burst from a Galactic core-collapse supernova. ALPs would be produced in the stellar medium via the Primakoff effect and convert into gamma rays in the Galactic magnetic field. Fermi LAT observations would be able to probe couplings where ALPs could constitute the entire dark matter. Below 1 neV, the Fermi-LAT sensitivity would surpass that of future laboratory experiments by one order of magnitude.

Speaker: Dr Manuel Meyer (Stockholm University, Oskar Klein Centre)

slides http://www.nordita.org/docs/agenda/slides-axions2016-meyer.pdf

16:00 → 16:30 Probing axions with core-collaspe supernovae

In this talk I will present an update of the axion bounds from a supernova explision based on the state-of-the art simulations. I will update the bound of photon-axion coupling from the non-observation of gamma-rays in coindicende with the SN 1987A. I will discuss the perspective of improvement in the case of observation of a future supernova with Fermi-LAT satellite. I will also revisit the bound on axions from supernova cooling and I will discuss the impact on future supernova neutrino observations

Speaker: Dr Alessandro Mirizzi (Dept. of Physics, University of Bari)

slides http://www.nordita.org/docs/agenda/slides-axions2016-mirizzi.pdf

16:30 → 17:00 Stellar cooling anomalies and the case of axions and axionlike particles

I will present an update on the axion bounds from stars and of the observed stellar cooling anomalies. I will discuss the interpretation of the observations in terms of axions and ALPs and show that they offer the most compelling solution among the various weakly interacting particles.

Speaker: Maurizio Giannotti (Barry University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-giannotti.pdf

17:00 → 17:30 Searches for modulation of gamma-ray spectra in the Galactic magnetic field as a signature of photon-ALPs mixing

Axion-like particles (ALPs) as an extension of the standard model define a generic class of light pseudo-sclars with a rich phenomenology because of their coupling to photons. Here we explore a so-far neglected opportunity to search for ALPs-photon coupling in the disappearance channel, i.e. a characteristic energy dependent suppression of gamma-rays. To verify this phenomenon we use seven years of Fermi-LAT Pass 8 data with P8R2_SOURCE_V6 IRFs of a selection f promising Galactic and Extragalactic sources and investigate the presence of spectral features of them in accordance with photon-ALPs coupling using particular models of the large-scale Galactic magnetic field. We estimate best fit values of parameters like photon-ALPs coupling and ALPs mass and we find that the signature of photon-ALPs mixing in inter galactic magnetictic field leads to an observable range.

Speaker: Mr Jhilik Majumdar (Institute for Experimental Physics, University of Hamburg)

slides http://www.nordita.org/docs/agenda/slides-axions2016-majumdar.pdf

17:30 → 18:00 Discussion

Thursday, 8 December

11:30 → 12:00 Ultra-High Field Solenoids and Axion Detection

The National High Magnetic Field Laboratory in Tallahassee Florida designs, builds, and operates the world's most powerful magnets; up to 45 T dc and 100 T for ~10 ms pulses. While most magnets are used for condensed-matter physics and have small bores (3 - 5 cm), large bore magnets have been demonstrated such as 11.4 T in a 60 cm bore or 13 T in a 50 cm bore.

Speaker: Ian Dixon (NHMFL-FSU)

slides http://www.nordita.org/docs/agenda/slides-axions2016-dixon.pdf

12:00 → 12:30 aKWISP: investigating short-range interactions at sub-micron scales. Status of the physics program at CAST

The sub-micron scale of distances in the field of short range interactions is presently not accessible to experimental investigation, and may hold the key to understanding al least part of the dark matter puzzle. The aKWISP (advanced-KWISP) proposal builds on the results obtained with the KWISP opto-mechanical, membrane-based, force sensor built at INFN Trieste, and now used in CAST to search for the direct matter coupling of solar chameleons in addition to the photon interaction channel. The current CAST physics program further extends its reach to dark matter axions, searching for them with RF cavities. aKWISP introduces the novel “double-membrane” concept, where interaction distances can be as short as 100 nm, much below the ≈10-30 micron distance which is the lower limit encountered by current experimental efforts. aKWISP reaches the ultimate quantum-limited sensitivity by exploiting an array of technologies, and by working at sub-Kelvin membrane temperatures. Thanks to a recent idea, short range intraction studies might further expand the possibilities also for the detection of axions.

Speaker: Prof. Giovanni Cantatore (University and INFN Trieste, CERN)

paper http://www.nordita.org/docs/agenda/slides-axions2016-cantatore.pdf

12:30 → 13:00 Status of IAXO

The international axion observatory is an initiative to build the next generation solar axion telescope. In this talk we will review the physics case, the proposed experiment and the status of the overall project.

Speaker: Javier Redondo (Zaragoza University)

slides http://www.nordita.org/docs/agenda/slides-axions2016-redondo-2.pdf

13:00 → 14:00 Lunch

14:00 → 14:30 CASPEr and GNOME experiments

These ongoing experiments search for oscillating and transient effects due to axions and ALPs.

Speaker: Dr Dmitry Budker (Helmholtz Institute Mainz)

slides http://www.nordita.org/docs/agenda/slides-axions2016-budker.pdf

14:30 → 15:00 MadMax: a new QCD Dark Matter Axion search

Axions can solve the Dark Matter and the strong CP problems. Most experimental efforts focus on axion masses < 20ueV. For Peccei-Quinn symmetry restoration after inflation the axion mass could be in the 100ueV range. A new project, MadMax, based on axion-photon conversion at the transition between different media is presented. A boost in axion-photon conversion of ~10^5 can be achieved using multiple layers. Within a 10T magnetic field this could be enough to achieve a detectable 100ueV axion-induced photon flux. The proposed design for an experiment is discussed. Results simulations and their comparison to noise, transmission, reflection and boost measurements in a prototype cavity will be presented. The expected sensitivity will be shown.

Speaker: Bela Majorovits (MPI fuer Physik)

slides http://www.nordita.org/docs/agenda/slides-axions2016-majorovits.pdf

15:00 → 15:30 Layered dielectric haloscopes: a new way to detect axion dark matter

Axions and axion-like particles are among the best-motivated candidates for dark matter. In particular, the QCD axion is capable of not only providing a dark matter candidate, but is also gives a natural explanation for the strong CP problem. Consequently, the detection of dark matter axions is of great interest as it would solve two of the most significant problems of modern physics. To this end, we introduce a new method to detect galactic dark-matter axions using dielectrics. When a dielectric interface is inside a strong parallel magnetic field, the oscillating axion field acts as a source of microwaves, which emerge in both directions perpendicular to the surface. These microwaves compensate for a discontinuity in the axion induced electric field. Crucially, the emission rate can be boosted by multiple parallel layers judiciously placed to achieve constructive interference. Starting from the axion-modified Maxwell equations, we calculate the efficiency of this new "layered dielectric haloscope? approach. This technique may prove useful in the well-motivated high-frequency range of 10-100 GHz (axion mass 40-400 ueV), where traditional cavity resonators have difficulties reaching the required volume. This would allow one to study axion dark matter generated by the topological defects, which occur if the reheating temperature after inflation was lower than the Peccei-Quinn scale. Unlike a cavity resonator it is possible for dielectric haloscopes to conduct a broadband search. In particular, we study the relation between the power generated and the bandwidth, the connection between the emission and reflection functions, and the connection to traditional cavity haloscopes.

Speaker: Alexander Millar (Max Planck Institute for Phyiscs)

slides http://www.nordita.org/docs/agenda/slides-axions2016-millar.pdf

15:30 → 16:00 High-field magnets at CAPP

Speaker: Jonghee Yoo (CAPP)

slides http://www.nordita.org/docs/agenda/slides-axions2016-yoo.pdf

16:00 → 16:30 Coffee break

16:30 → 17:00 Constraints on axion properties from cosmological observations

Axions can be produced in the early Universe through thermal or nonthermal processes. In the former case, they contribute to the cosmological energy budget as a hot dark matter component, while in the latter they could be the cold dark matter component. Moreover, if the breaking of the Peccei-Quinn symmetry happens during inflation, quantum fluctuations in the axion field will give rise to isocurvature perturbations. In my talk I will present constraints that can be put on axion properties from cosmological observations, mainly focusing on measurements of the anisotropies of the cosmic microwave background from the Planck satellite. I will also comment on the effect of theoretical uncertainties on estimates of axion parameters.

Speaker: Massimiliano Lattanzi (Universita di Ferrara)

notype http://www.nordita.org/docs/agenda/slides-axions2016-lattanzi.pdf

17:00 → 17:30 Limits on Cosmic ALPs Background from cosmic reionization

Recently it has been pointed out that a cosmic background of relativistic axion-like particles (ALPs) would be produced by the primordial decays of heavy fields(moduli) in the post-inflation epoch, contributing to the extra-radiation content in the Universe today. Primordial magnetic fields would trigger conversions of these ALPs into sub-MeV photons during the dark ages. This photon flux would produce an early reionization of the Universe, leaving a significant imprint on the total optical depth to recombination ?. Using the current measurement of ? and the limit on the extra-radiation content ?Neff by the Planck experiment we put a strong bound on the ALP-photon conversions.

Speaker: Dr Daniele Montanino (Universita del Salento and INFN, Lecce)

slides http://www.nordita.org/docs/agenda/slides-axions2016-montanino.pdf

17:30 → 18:00 Concluding Talk

Speaker: Dr Axel Lindner (DESY)

slides http://www.nordita.org/docs/agenda/slides-axions2016-lindner-2.pdf

18:30 → 20:30 Reception

Friday, 9 December

09:00 → 14:00 Discussions