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.
17452272
The Pion Cloud in Quenched QCD
Diagrammatic methods and Large $N_c$ QCD are used to argue that the nucleon as calculated in quenched QCD contains physics which can be ascribed to the pion cloud of the nucleon. In particular, it is argued that the physics corresponding to one-pion loops in chiral perturbation theory are included in the quenched approximation.
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.
118487970
Testing the QCD string at large Nc from the thermodynamics of the hadronic phase
It is generally believed that in the limit of a large number of colors (Nc) the description of confinement via flux tubes becomes valid and QCD can be modeled accurately via a hadronic string theory—at least for highly excited states. QCD at large Nc also has a well‐defined deconfinement transition at a temperature Tc. In this talk it is shown how the thermodyanmics of the metastable hadronic phase of QCD (above Tc) at large NC can be related directly to properties of the effective QCD string. The key points in the derivation is the weakly interacting nature of hadrons at large Nc and the existence of a Hagedorn temperature TH for the effective string theory. From this it can be seen at large Nc and near TH, the energy density and pressure of the hadronic phase scale as E ∼ (TH − T)−(D⊥−6)/2 (for D⊥ < 6) and P ∼ (TH − T)−(D⊥−4)/2 (for D⊥ < 4) where D⊥ is the effective number of transverse dimensions of the string theory. This behavior for D⊥ < 6 is qualitatively different from typical models in statistica...
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.
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.
53390439
Boosting stop searches with a 100 TeV proton collider
A bstractA proton-proton collider with center of mass energy around 100 TeV is the energy frontier machine that is likely to succeed the LHC. One of the primary physics goals will be the continued exploration of weak scale naturalness. Here we focus on the pair-production of stops that decay to a top and a neutralino. Most of the heavy stop parameter space results in highly boosted tops, populating kinematic regimes inaccessible at the LHC. New strategies for boosted top-tagging are needed and a simple, detector-independent tagger can be constructed by requiring a muon inside a jet. Assuming 20% systematic uncertainties, this future collider can discover (exclude) stops with masses up to 5.5 (8) TeV with 3000 fb−1 of integrated luminosity. Studying how the exclusion limits scale with luminosity motivates going beyond this benchmark in order to saturate the discovery potential of the machine.
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.
119227010
Wino dark matter under siege
A fermion triplet of SU(2)L — a wino — is a well-motivated dark matter candidate. This work shows that present-day wino annihilations are constrained by indirect detection experiments, with the strongest limits coming from H.E.S.S. and Fermi. The bounds on wino dark matter are presented as a function of mass for two scenarios: thermal (winos constitute a subdominant component of the dark matter for masses less than 3.1 TeV) and non-thermal (winos comprise all the dark matter). Assuming the NFW halo model, the H.E.S.S. search for gamma-ray lines excludes the 3.1 TeV thermal wino; the combined H.E.S.S. and Fermi results completely exclude the non-thermal scenario. Uncertainties in the exclusions are explored. Indirect detection may provide the only probe for models of anomaly plus gravity mediation where the wino is the lightest superpartner and scalars reside at the 100 TeV scale.
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.