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.
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.
118984899
Singlet-Doublet Dark Matter
In light of recent data from direct detection experiments and the Large Hadron Collider, we explore models of dark matter in which an SU(2){sub L} doublet is mixed with a Standard Model singlet. We impose a thermal history. If the new particles are fermions, this model is already constrained due to null results from XENON100. We comment on remaining regions of parameter space and assess prospects for future discovery. We do the same for the model where the new particles are scalars, which at present is less constrained. Much of the remaining parameter space for both models will be probed by the next generation of direct detection experiments. For the fermion model, DeepCore may also play an important role.
17675959
Leptophilic dark matter from the lepton asymmetry.
We present a model of weak scale dark matter (DM) where the thermal DM density is set by the lepton asymmetry due to the presence of higher dimension lepton violating operators. In these models there is generically a separation between the annihilation cross section responsible for the relic abundance (through lepton violating operators) and the annihilation cross section that is relevant for the indirect detection of DM (through lepton preserving operators). This implies a perceived boost in the annihilation cross section in the Galaxy today relative to that derived for canonical thermal freeze-out, giving a natural explanation for the observed cosmic ray electron and positron excesses, without resorting to a Sommerfeld enhancement. These models motivate continued searches for DM with apparently nonthermal annihilation cross sections. The DM may also play a role in radiatively generating Majorana neutrino masses.
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.
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.
20988932
On the existence of heavy pentaquarks: The large N c and heavy quark limits and beyond
We present a very general argument that the analogue of a heavy pentaquark (a state with the quantum numbers of a baryon combined with an additional light quark and a heavy antiquark Q) must exist as a particle stable under strong interactions in the combined heavy quark and large N{sub c} limits of QCD. Moreover, in the combined limit these heavy pentaquark states fill multiplets of SU(4)xO(8)xSU(2). We explore the question of whether corrections in the combined 1/N{sub c} and 1/m{sub Q} expansions are sufficiently small to maintain this qualitative result. Since no model-independent way is known to answer this question, we use a class of realistic hadronic models in which a pentaquark can be formed via nucleon-heavy-meson binding through a pion-exchange potential. These models have the virtue that they necessarily yield the correct behavior in the combined limit, and the long-distance parts of the interactions are model independent. If the long-distance attraction in these models were to predict bound states in a robust way (i.e., largely insensitive to the details of the short-range interaction), then one could safely conclude that heavy pentaquarks do exist. However, in practice the binding does depend very strongly on the details of the short-distancemore » physics, suggesting that the real world is not sufficiently near the combined large N{sub c}, m{sub Q} limit to use it as a reliable guide. Whether stable heavy pentaquarks exist remains an open question.« less
119356537
Regularization, renormalization, and range: The nucleon-nucleon interaction from effective field theory
Regularization and renormalization is discussed in the context of low energy effective field theory treatments of two or more heavy particles (such as nucleons). It is desirable to regulate the contact interactions from the outset by treating them as having a finite range. The low energy physical observables should be insensitive to this range provided that the range is of a similar or greater scale than that of the interaction. Alternative schemes, such as dimensional regularization, lead to paradoxical conclusions such as the impossibility of repulsive interactions for truly low energy effective theories where all of the exchange particles are integrated out. This difficulty arises because a nonrelativistic field theory with repulsive contact interactions is trivial in the sense that the S matrix is unity and the renormalized coupling constant zero. Possible consequences of low energy attraction are also discussed. It is argued that in the case of large or small scattering lengths, the region of validity of effective field theory expansion is much larger if the contact interactions are given a finite range from the beginning. {copyright} {ital 1997} {ital The American Physical Society}
119052453
Meson coupling constants at high mass and large Nc
Abstract Quark–hadron duality implies that a process described in terms of quark loops should be the hadronic amplitude when averaged over a sufficient number of states. Ambiguities associated with the notion of quark–hadron duality can be made arbitrarily small for highly excited mesons at large N c . QCD is expected to form a string like description at large N c yielding an exponentially increasing Hagedorn spectrum for high mass. It is shown that in order to reconcile quantum–hadron duality with a Hagedorn spectrum, the magnitude of individual coupling constants between high-lying mesons in a typical decay process must be characteristically larger than the average of the coupling constants to mesons with nearby masses. The ratio of the square of the average coupling to the average of the coupling squared (where the average is over mesons with nearby masses) drops exponentially with the mass of the meson. Scenarios are discussed by which such a high precision cancellation can occur.
119301914
Total nucleon-nucleon cross sections in large Nc QCD
We use contracted spin-flavor symmetry which emerges in the large Nc limit of QCD to obtain relations between proton-proton and proton-neutron total cross sections for both polarized and unpolarized scattering. The formalism used is valid in the semi-classical regime in which the relative momentum of the incident nucleons is much larger than the inverse size of the nucleon, provided that certain technical assumptions are met. The relations should be phenomenologically useful provided that Nc=3 is sufficiently large so that the large Nc results have at least semi-quantitative predictive power. The relations are model-independent in the sense that they depend on properties of large Nc QCD only and not on any particular model-dependent details of the nucleon-nucleon interaction. We compare these model-independent results to experimental data. We find the relation for spin-unpolarized scattering works well empirically. For the case of polarized scattering, the data is consistent with the relations but the cross sections are too small to make sharp predictions.
119421850
SU(3) Clebsch-Gordan coefficients for baryon-meson coupling at arbitrary N c
We present explicit formulas for the SU(3) Clebsch-Gordan coefficients that are relevant for the couplings of large N{sub c} baryons to mesons. In particular, we compute the Clebsch-Gordan series for the coupling of the octet (associated with mesons, and remains the correct representation at large N{sub c}) to the large N{sub c} analogs of the baryon octet and decuplet representations.