Challenges in the Dark Sector: Alternatives to the WIMP paradigm

16 Dec 2015, 09:00 → 18 Dec 2015, 18:00 Europe/Rome

High Energy Building, Seminar Room (Laboratori Nazionali di Frascati)

Barbara Mele (ROMA1), Enrico Nardi (LNF), Gennaro Corcella (LNF), Giuseppe Degrassi (ROMA3), Mauro Raggi (ROMA1)

Aim of the workshop:

Identifying what Dark Matter (DM) is, as well as its nature and properties, remains a major challenge for both theoretical and experimental astroparticle physics communities. In the past decades, Weakly Interacting Massive Particle (WIMP) DM has been the most hunted candidate, with the result that nowadays WIMPs are cornered by large amounts of experimental data from Direct Detection, Indirect Detection and Collider Experiments. If no WIMP signal is detected in the next few years, the possibility that this very appealing theoretical idea is not what Nature has chosen will become even more compelling and will boost theoretical studies and experimental searches for non-WIMP alternatives for DM.
The aim of this 3-day meeting is to convene experts on alternatives to the WIMP paradigm to stimulate informal discussions on different possibilities (dark photons, axion-like particles, Majorons, self-interacting dark sectors, just to mention a few). We plan to have only three or four talks each day and plenty of time to discuss implications of these DM scenarios, experimental search strategies, new theoretical proposals, and out-of-mainstream ideas. The general approach and format of the talks will be pedagogical and aimed at favoring extended discussions among all participants. The audience will range from theorists who are expert on related topics to skillful experimentalists planning new non-WIMP detection experiments, as well as postdocs, graduate students and non-expert colleagues working in different areas.

Speakers:

J. Beacham     (Ohio State U. & CERN)
"Lost in a Dark Photon Wood: Searches for hidden light gauge bosons at colliders" 
A. Dolgov          (NSU, Novosibirsk & U. Ferrara) 
"Millicharged particles: a review " 
N. Fornengo       (U. Torino)  
"Status of the WIMP miracle"   
F. Kahlhoefer      (DESY) 
"Searching for dark matter and pseudoscalar mediators at the intensity frontier" 
Hye-Sung Lee    (IBS, Daejeon Korea)
"Dark bosons and the g-2 anomaly"        
A. Lindner          (DESY)                                                
"Axion and WISP searches in Labs"
J. Pradler          (Vienna, OAW)
“Astrophysical and cosmological aspects of Dark Photons" 
J. Redondo        (Zaragoza U. & Munich, Max Planck Inst.)
"Axion Cosmology and Astrophysics"                                
M. Roncadelli     (INFN, Pavia) 
"Astrophysical gamma-ray probes of ALPs"                        
S. Tulin             (York U., Canada)                 
"Self interacting Dark Matter"     

Wednesday, 16 December

10:00 → 11:30 Status of the WIMP Miracle

The talk will review the concept of WIMPs as dark matter candidates and will discuss its realization in some selected particle physics models. It will then outline the way WIMP dark matter is searched for in the astrophysical environment, the current status of these searches and their prospects for the future.

Speaker: Nicolao Fornengo (TO)

Slides fornengo.pdf

11:30 → 13:00 Axions and WISPs searches in Labs

In the recent years Weakly Interacting Slim Particles (WISPs), with the axion being it’s most famous representative, have caught increasing interest in theoretical and experimental physics. Presently a number of experiments are taking data or are being prepared to look for dark matter WISPs, solar WISPs or WISPs generated in the laboratory. For the first time these approaches will allow to probe a large fraction of the parameter space for axions constituting the dark matter and for axion-like particles explaining puzzling astrophysical phenomena. This talk will give an overview on such running and planned experiments.

Speaker: Axel Lindner (DESY)

Slides WISP-Searches.pdf

14:30 → 16:00 Astrophysical gamma-ray probes of ALPs

Axion-like particles (ALPs) are quite similar to the axion and are predicted by several extensions of the Standard Models, especially by superstring theories. However, at variance with the axion, they couple only to two photons, and this fact makes them quite elusive. Yet, since 2007 it has been recognized that they can play a crucial role in high-energy astrophysics. This talk reports some results that have been obtained in this field, and especially some hints of their existence arising from the fact that they solve some observed anomalies. The possibility that they are cold dark matter candidates is stressed, along with the fact that for the model parameters required by the above hints they can be detected at ALPS II and IAXO.

Speaker: Marco Roncadelli (PV)

Slides Talk_Frascati_-_Roncadelli.pdf

Thursday, 17 December

10:00 → 11:30 Axion Cosmology and Astrophysics

Axions are one of the most motivated candidates for the dark matter of the universe. In this talk I review the paradigm of axion dark matter and describe current experimental searches to find the axion as dark matter itself and in other laboratory experiments like IAXO, a proposed axion solar telescope.

Speaker: Javier Redondo (Zaragoza U.& Munich, Max Planck Inst.)

Slides AxionAstroDM.key

11:30 → 13:00 Millicharged particles. A review

Cosmological effects of hypothetical millicharged particles and experimental bounds on their existence are considered. Such particles may make a fraction or 100% contribution to dark matter in the universe. If they are light, they could be warm dark matter and alleviate problems of cold dark matter cosmology. This particles can also solve the long standing problem of large scale cosmic magnetic fields. Their existence can be proved or disproved by direct experiments with somewhat improved sensitivity.

Speaker: Alexander Dolgov (FE)

14:30 → 16:00 Self interacting Dark Matter

Astrophysical observations of the structure of galaxies and clusters are no longer simply proving the existence of DM, but have sharpened into a tool probing the particle physics of DM. I review small scale structure anomalies for CDM and their possible implications for DM physics, such as the existence of forces in the dark sector. New results on cluster scales provide a new important handle for constraining DM's interactions, its mass, and the mass of dark mediator particles. I discuss how self-interactions arise in particle physics models and complementarity with other types of dark matter searches.

Speaker: Sean Tulin (York University)

Slides frascati15.pdf

16:00 → 17:30 Searching for dark matter and pseudoscalar mediators at the intensity frontier

I will consider scenarios where dark matter interacts with Standard Model states via the exchange of a light pseudoscalar. While there are typically only weak constraints from direct dark matter searches, the pseudoscalar mediator will induce new interactions between Standard Model particles, providing a promising alternative way to test these models. I will present the constraints arising from rare meson decays and fixed target experiments, with a special focus on how to reliably calculate the production of axion-like particles in proton beam fixed-target experiments such as NA62 or SHiP. The resulting bounds are highly complementary to the information inferred from the dark matter relic density and the constraints from primordial nucleosynthesis. These findings have important implications for the dark matter self-interaction cross section and the prospects of probing dark matter coupled to a light pseudoscalar with direct or indirect detection experiments.

Speaker: Felix Kahlhoefer (DESY)

Slides Frascati.pdf

Friday, 18 December

10:00 → 11:30 Astrophysical and Cosmological aspects of Dark Photons

This talk will highlight astrophysical and cosmological implications of dark photons in the keV - MeV mass bracket. A kinetically mixed vector particle with mass below the electron mass is a viable candidate for dark matter. I will show how direct detection experiments are probing to this “superWIMP” scenario, and present competing astrophysical constraints. In a second part, I will focus on the framework of primordial nucleosynthesis and show how it puts new physics in the MeV mass range to the test. In addition to dark photons, I will also present a new solution to the cosmological lithium problem that is based on ALPs and that is also testable in intensity frontier experiments.

Speaker: Josef Pradler (Vienna OAW)

Slides Frascati_JP.pdf

11:30 → 13:00 Dark bosons and the g-2 anomaly

A dark gauge boson typically refers to a very light gauge boson with very small couplings to the Standard Model particles. It can be motivated from various phenomena, and one of them is the explanation of the 3.6 sigma level deviation in the muon anomalous magnetic moment. We will go over a couple of dark gauge boson models that can address this issue and overview the experimental constraints. We will emphasize the importance of the low-energy parity test as some of the models predict the change of the effective Weinberg angle in the low-energy experiments.

Speaker: Hye-Sung Lee (IBS, Daejeon Korea)

Slides Dark_bosons_and_the_g-2_anomaly_(Frascati_2015).pdf

14:30 → 16:00 Lost in a Dark Photon Wood: Searches for Hidden Light Gauge Bosons at Colliders

The past several years have seen an explosion in experimental searches for new low-mass gauge bosons (dark photons, hidden gauge bosons, A-primes, U-bosons, etc.) at colliders. Much of this activity stems from the intriguing prospect that such a particle with a mass of ~1 GeV could serve as an explanation for anomalies seen in non-collider based dark matter experiments. But as the collider experiments have been designed and performed, the theoretical motivation has developed robustly in parallel, resulting in a rich set of well-motivated production and decay modes — both to Standard Model particles and to invisible states — of low-mass hidden gauge bosons to be sought after in collider experiments. I will review the foundational collider beam dump experiments and other constraints from astrophysical data, describe the recent and current searches being performed at low-energy fixed target experiments and high-energy hadron colliders, and briefly touch upon the prospects and challenges at future circular colliders and even more speculative possibilities.

Speaker: James Beacham (Ohio State U. & CERN)

Slides Beacham_Challenges_Dark_Sector_Frascati_2015Dec.pdf