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Register a new userProbing the axion-photon coupling: phenomenological and experimental perspectives. A snowmass white paper
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G. Carosi
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We present a brief overview of the ongoing searches for the axion particle via its coupling to photons. Both the classical QCD axions and more recently proposed Axion-Like-Particles are considered. Astrophysical bounds on the axion-photon coupling come from considerations of stellar energy loss during Helium burning, in both low- and high-mass stars. Helioscopes look for back-conversion of solar axions into x-ray photons in strong laboratory magnetic fields. Finally, haloscopes aim to detect dark matter axions in our galactic halo. Both types of searches are expecting significant advances in the future, which will enable them to probe large, well-motivated parts of the parameter space below the stellar cooling bounds.
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Stops with the mass nearly degenerate with the top mass, decaying into tops and soft neutralinos, are usually dubbed stealth stops. Their kinematics looks very similar to that of the standard tops events, which leads to events with little or no excess of missing transverse energy. This complicates the probing of this region of the stop parameter space by hadron colliders, rendering the application of standard searching techniques challenging. In this Snowmass white paper we reanalyze the spin correlation approach to the search of stealth stops, focusing on the feasibility of this search at the 14 TeV LHC. We find, while the statistical limitations significantly shrink compared to the low-luminosity 8 TeV run, the systematic PDF uncertainties pose the main obstacle. We show that the current understanding of PDFs probably does not allow us to talk about top and stop discrimination via spin correlation in the inclusive sample. On the other hand the systematic uncertainties significantly shrink if only events with low center of mass energy are considered, rendering the search in this region feasible.
Neutrino masses are clear evidence for physics beyond the standard model and much more remains to be understood about the neutrino sector. We highlight some of the outstanding questions and research opportunities in neutrino theory. We show that most of these questions are directly connected to the very rich experimental program currently being pursued (or at least under serious consideration) in the United States and worldwide. Finally, we also comment on the state of the theoretical neutrino physics community in the U.S.
A portion of light scalar dark matter, especially axions, may organize into gravitationally bound clumps (stars) and be present in large number in the galaxy today. It is therefore of utmost interest to determine if there are novel observational signatures of this scenario. Work has shown that for moderately large axion-photon couplings, such clumps can undergo parametric resonance into photons, for clumps above a critical mass $M^{star}_c$ determined precisely by some of us in Ref. [1]. In order to obtain a clump above the critical mass in the galaxy today would require mergers. In this work we perform full 3-dimensional simulations of pairs of axion clumps and determine the conditions under which mergers take place through the emission of scalar waves, including analyzing head-on and non-head-on collisions, phase dependence, and relative velocities. Consistent with other work in the literature, we find that the final mass from the merger $M^{star}_{text{final}}approx 0.7(M^{star}_1+M^{star}_2)$ is larger than each of the original clump masses (for $M^{star}_1sim M^{star}_2$). Hence, it is possible for sub-critical mass clumps to merge and become super-critical and therefore undergo parametric resonance into photons. We find that mergers are expected to be kinematically allowed in the galaxy today for high Peccei-Quinn scales, which is strongly suggested by unification ideas, although the collision rate is small. While mergers can happen for axions with lower Peccei-Quinn scales due to statistical fluctuations in relative velocities, as they have a high collision rate. We estimate the collision and merger rates within the Milky Way galaxy today. We find that a merger leads to a flux of energy on earth that can be appreciable and we mention observational search strategies.
This paper summarizes discussions of the theoretical developments and the studies performed by the NNbarX collaboration for the 2013 Snowmass Community Summer Study.
In this Snowmass White Paper, we discuss physics opportunities involving heavy quarkonia at the intensity and energy frontiers of high energy physics. We focus primarily on two specific aspects of quarkonium physics for which significant advances can be expected from experiments at both frontiers. The first aspect is the spectroscopy of charmonium and bottomonium states above the open-heavy-flavor thresholds. Experiments at e^+ e^- colliders and at hadron colliders have discovered many new, unexpected quarkonium states in the last 10 years. Many of these states are surprisingly narrow, and some have electric charge. The observations of these charged quarkonium states are the first definitive discoveries of manifestly exotic hadrons. These results challenge our understanding of the QCD spectrum. The second aspect is the production of heavy quarkonium states with large transverse momentum. Experiments at the LHC are measuring quarkonium production with high statistics at unprecedented values of p_T. Recent theoretical developments may provide a rigorous theoretical framework for inclusive production of quarkonia at large p_T. Experiments at the energy frontier will provide definitive tests of this framework. Experiments at the intensity frontier also provide an opportunity to understand the exclusive production of quarkonium states.
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