18819303
Baryons and baryonic matter in the large Nc and heavy quark limits
This paper explores properties of baryons and finite density baryonic matter in an artificial world in which N{sub c}, the number of colors, is large and the quarks of all species are degenerate and much larger than {Lambda}{sub QCD}. It has long been known that in large N{sub c} quantum chromodynamics (QCD), baryons composed entirely of heavy quarks are accurately described in the mean-field approximation. However, the detailed properties of baryons in the combined large N{sub c} and heavy-quark limits have not been fully explored. Here some basic properties of baryons are computed using a variational approach. At leading order in both the large N{sub c} and heavy-quark expansions the baryon mass is shown to be M{sub baryon}{approx_equal}N{sub c}M{sub Q}(1-0.054 26{alpha}-tilde{sub s}{sup 2}), where {alpha}-tilde{sub s}{identical_to}N{sub c}{alpha}s. The baryon form factor is also computed. Baryonic matter, the analog of nuclear matter in this artificial world, should also be well described in the mean-field approximation. In the special case where all baryons have an identical spin-flavor structure, it is shown that in the formal heavy-quark and large N{sub c} limit interactions between baryons are strictly repulsive at low densities. The energy per baryon is computed in this limit and found tomore » be exponentially small. It is shown that when the restriction to baryons with an identical spin-flavor structure is dropped, a phase of baryonic matter exists with a density of 2N{sub f} times that for the restricted case but with the same energy (where N{sub f} is the number of degenerate flavors). It is shown that this phase is at least metastable.« less
118729457
A sticky business: the status of the conjectured viscosity/entropy density bound
There have been a number of forms of a conjecture that there is a universal lower bound on the ratio, η/s, of the shear viscosity, η, to entropy density, s, with several different domains of validity. We examine the various forms of the conjecture. We argue that a number of variants of the conjecture are not viable due to the existence of theoretically consistent counterexamples. We also note that much of the evidence in favor of a bound does not apply to the variants which have not yet been ruled out.
29345433
Quark and gluon condensates in nuclear matter.
Quark and gluon condensates in nuclear matter are studied. These in-medium condensates may be linked to a wide range of nuclear phenomena and are important inputs to QCD sum-rule calculations at finite density. The Hellmann-Feynman theorem yields a prediction of the quark condensate that is model independent to first order in the nucleon density. This linear density dependence, with slope determined by the nucleon {sigma} term, implies that the quark condensate is reduced considerably at nuclear matter saturation density---it is roughly 25--50 % smaller than the vacuum value. The trace anomaly and the Hellmann-Feynman theorem lead to a prediction of the gluon condensate that is model independent to first order in the nucleon density. At nuclear matter saturation density, the gluon condensate is about 5% smaller than the vacuum value. Contributions to the in-medium quark condensate that are of higher order in the nucleon density are estimated with mean-field quark-matter calculations using the Nambu--Jona-Lasinio and Gell-Mann--Levy models. Treatments of nuclear matter based on hadronic degrees of freedom are also considered, and the uncertainties are discussed.
119429672
Systematic power counting in cutoff effective field theories for nucleon-nucleon interactions and the equivalence with PDS
Abstract An analytic expression for the 1 S 0 phase shifts in nucleon-nucleon scattering is derived in the context of the Schrodinger equation in configuration space with a short distance cutoff and with a consistent power counting scheme including pionic effects. The scheme treats the pion mass and the inverse scattering length over the intrinsic short distance scale as small parameters. Working at next-to-leading order in this scheme, we show that the expression obtained is identical to one obtained using the recently introduced PDS approach which is based on dimensional regularization with a novel subtraction scheme. This strongly supports the conjecture that the schemes are equivalent provided one works to the same order in the power counting.
33491035
Color-dielectric models from a lattice point of view.
We study the color-dielectric model, introduced by Nielsen and Patkos, using lattice gauge theory. We argue that the collective color-dielectric field, which is introduced by a block-spinning method, approaches zero in the vacuum for confining theories for a sufficiently large averaging size of the block-spinning box, as a consequence of the area-law behavior of Wilson loops. Increasing the box size increases the effective potential height for quarks, but decreases the resolving power of the effective theory. Estimates show that there exists an optimal choice of the size of the box suitable for a mean-field description of hadrons within the color-dielectric models with confinement. This yields a limit for the maximum momentum scales for which these models are applicable. This limit poses no difficulties for construction of phenomenological models.
126291695
Nuclear and Hadronic Physics at Large N c
This talk briefly surveys some of the advances in large Nc QCD in nuclear and hadronic physics during the past decade or so. It highlights recent results including an analytic result for the total nucleon-nucleon cross section in nucleon-nucleon scattering in the extreme large Nc limit (logNc 1)); it is given by s total = 2p log 2 (Nc) m 2 for p s much larger than the QCD scale. The talk also stresses a demonstration that given certain technical assumptions, it can be shown that QCD must have a Hagedorn spectrum (i.e., a spectrum where the number of hadrons grows exponentially with hadron mass) . Another theme in the talk is the phenomenology of a variant of the large Nc limit based on quarks in the two-index antisymmetric representation. This variant of large Nc QCD is qualitatively different from the conventional one in which quarks are in the fundamental representation and corresponds to a distinct large Nc limit with a distinct 1=Nc expansion. The description of nuclear forces and nuclear matter in both variants of the largeNc limit are discussed.
10334629
A Comparison of Future Proton Colliders Using SUSY Simplified Models: A Snowmass Whitepaper
We present a summary of results for SUSY Simplified Model searches at future proton colliders: the 14 TeV LHC as well as a 33 TeV proton collider and a 100 TeV proton collider. Upper limits and discovery significances are provided for the gluino-neutralino (for both light and heavy flavor decays), squark-neutralino, and gluino-squark Simplified Model planes. Events are processed with the Snowmass combined detector and Standard Model backgrounds are computed using the Snowmass samples. We place emphasis on comparisons between different collider scenarios, along with the lessons learned regarding the impact of systematic errors and pileup. More details are provided in a companion paper.
118415332
Electroweak Baryogenesis and Higgs Signatures
We explore the connection between the strength of the electroweak phase transition and the properties of the Higgs boson. Our interest is in regions of parameter space that can realize electroweak baryogenesis. We do so in a simplified framework in which a single Higgs field couples to new scalar fields charged under $SU(3{)}_{c}$ by way of the Higgs portal. Such new scalars can make the electroweak phase transition more strongly first-order, while contributing to the effective Higgs boson couplings to gluons and photons through loop effects. For Higgs boson masses in the range $115\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{h}\ensuremath{\lesssim}130\text{ }\text{ }\mathrm{GeV}$, whenever the phase transition becomes strong enough for successful electroweak baryogenesis, we find that Higgs boson properties are modified by an amount observable by the LHC. We also discuss the baryogenesis window of the minimal supersymmetric standard model (MSSM), which appears to be under tension. Furthermore, we argue that the discovery of a Higgs boson with standard model-like couplings to gluons and photons will rule out electroweak baryogenesis in the MSSM.
119159310
Asymmetric Dark Matter from a GeV Hidden Sector
Asymmetric dark matter (ADM) models relate the dark matter (DM) density to the baryon asymmetry, so that a natural mass scale for ADM is around a few GeV. In existing models of ADM, this mass scale is unexplained; here we generate this GeV scale for DM) from the weak scale via gauge kinetic mixing with a new Abelian dark force. In addition, this dark sector provides an efficient mechanism for suppressing the symmetric abundance of DM through annihilations to the dark photon. We augment this sector with a higher dimensional operator responsible for communicating the baryon asymmetry to the dark sector. Our framework also provides a DM candidate for gauge mediation models. It results in a direct detection cross section of interest for current experiments: {sigma}{sub p} < or approx. 10{sup -41} cm{sup 2} for DM masses in the range 1-15 GeV.
59031368
Illuminating the 130 GeV gamma line with continuum photons
A bstractThere is evidence for a 130 GeV γ-ray line at the Galactic Center in the Fermi Large Area Telescope data. Dark matter candidates that explain this feature should also annihilate to Standard Model particles, resulting in a continuous spectrum of photons. To study this continuum, we analyze the Fermi data down to 5 GeV, restricted to the inner 3◦ of the Galaxy. We place a strong bound on the ratio of continuum photons to monochromatic line photons that is independent of uncertainties in the dark matter density profile. The derived constraints exclude neutralino dark matter as an explanation for the line.
118834481
Here be dragons: the unexplored continents of the CMSSM
A bstractThe Higgs boson mass and the abundance of dark matter constrain the CMSSM/mSUGRA supersymmetry breaking inputs. A complete map of the CMSSM that is consistent with these two measured quantities is provided. Various “continents”, consisting of non-excluded models, can be organized by their dark matter dynamics. The following mechanisms manifest: well-tempering, resonant pseudo-scalar Higgs annihilation, neutralino/stau coannihilations and neutralino/stop coannihilations. Benchmark models are chosen in order to characterize the viable regions. The expected visible signals of each are described, demonstrating a wide range of predictions for the 13 TeV LHC and a high degree of complementarity between dark matter and collider experiments. The parameter space spans a finite volume, which can be probed in its entirety with experiments currently under consideration.