Abstract
We study the conserved charge fluctuations, as quantified by the corresponding susceptibilities, in strongly interacting matter as motived by the quark-gluon plasma. Using the gauge-gravity correspondence approach, we study the patterns of conserved charge fluctuations in two types of holographic models for QCD, the D4/D8 and the D3/D7 models. We compute and compare the quark number susceptibilities in both models and find an interesting common feature of the two: at very strong coupling higher order susceptibilities are suppressed and the conserved charge fluctuations become purely Guassian. In light of the state-of-the-art lattice QCD results we also discuss what we can learn from these susceptibilities about the underlying degrees of freedom in the 1 ~ 2T c quark-gluon plasma and examine the viability of different ideas such as holography, quasi-particles, as well as bound states. From analyzes of second order susceptibilities we conclude that the bound states exist and are important in the 1 ~ 2T c region. We further construct and make predictions for several ratios of fourth-order susceptibilities that can sensitively reveal such bound states.
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Shi, S., Liao, J. Conserved charge fluctuations and susceptibilities in strongly interacting matter. J. High Energ. Phys. 2013, 104 (2013). https://doi.org/10.1007/JHEP06(2013)104
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DOI: https://doi.org/10.1007/JHEP06(2013)104