We study an SU(3) gauge theory with N f = 8 degenerate flavors of light fermions in the fundamental representation. Using the domain wall fermion formulation, we investigate the light hadron spectrum, chiral condensate ψψ and electroweak S parameter. We consider a range of light fermion masses on two lattice volumes at a single gauge coupling chosen so that IR scales approximately match those from our previous studies of the two-and six-flavor systems. Our results for the N f = 8 spectrum suggest spontaneous chiral symmetry breaking, though fits to the fermion mass dependence of spectral quantities do not strongly disfavor the hypothesis of mass-deformed infrared conformality. Compared to N f = 2 we observe a significant enhancement of ψψ relative to the symmetry breaking scale F , similar to the situation for N f = 6. The reduction of the S parameter, related to parity doubling in the vector and axial-vector channels, is also comparable to our six-flavor results.

We present the spectrum of baryons in a new SU(4) gauge theory with fundamental fermion constituents. The spectrum of these bosonic baryons is of significant interest for composite dark matter theories. Here, we compare the spectrum and properties of SU(3) and SU(4) baryons, and then compute the dark-matter direct detection cross section via Higgs boson exchange for TeVscale composite dark matter arising from a confining SU(4) gauge sector. Comparison with the latest LUX results leads to tight bounds on the fraction of the constituent-fermion mass that may arise from electroweak symmetry breaking. Lattice calculations of the dark matter mass spectrum and the Higgs-dark matter coupling are performed on quenched 16 3 × 32, 32 3 × 64, 48 3 × 96, and 64 3 ×128 lattices with three different lattice spacings, using Wilson fermions with moderate to heavy pseudoscalar meson masses. Our results lay a foundation for future analytic and numerical study of composite baryonic dark matter.

Composite dark matter candidates, which can arise from new strongly-coupled sectors, are wellmotivated and phenomenologically interesting, particularly in the context of asymmetric generation of the relic density. In this work, we employ lattice calculations to study the electromagnetic form factors of electroweak-neutral dark-matter baryons for a three-color, QCD-like theory with N f = 2 and 6 degenerate fermions in the fundamental representation. We calculate the (connected) charge radius and anomalous magnetic moment, both of which can play a significant role for direct detection of composite dark matter. We find minimal N f dependence in these quantities. We generate mass-dependent cross-sections for dark matter-nucleon interactions and use them in conjunction with experimental results from XENON100, excluding dark matter candidates of this type with masses below 10 TeV.PACS numbers: 11.10. Hi, 11.15.Ha, 95.35.+d Introduction Experimental bounds on the interaction of the dark matter with Standard-Model (SM) particles have strengthened by many orders of magnitude in recent years. In particular, dark-matter particles cannot have SMstrength couplings to electroweak gauge bosons, based on direct-detection constraints [1, 2]. At the same time, there is a strong motivation for the dark matter to couple to the SM in some way for the purpose of relic density generation, either as a thermal relic via the so-called "WIMP miracle" (see [3] for a recent review) or through an asymmetric scenario which may be related to the creation of baryon asymmetry [4][5][6][7][8][9][10][11]. Construction of dark matter models thus requires a careful balance between the presence and absence of dark-sector interactions with the SM.Composite dark matter models provide a simple mechanism for attaining this balance, one which can lead to interesting and unique phenomenology. By hypothesizing a new, confining gauge force in the dark sector, an electroweak-neutral composite dark matter candidate can be constructed as a bound state of electroweak-charged constituents. In this way, electroweak interactions can be active in the early Universe for the generation of relic density, but only neutral bound states survive to the present day. Electroweak coupling to the constituents is still possible, leading to form-factor suppressed interactions with the neutral composites. They can be roughly estimated from QCD analogs, but in general can be determined quantitatively only by lattice calculations.In this paper, we consider an underlying SU (3) gauge theory with fermions in the fundamental representation, but

Using lattice simulations, we study the infrared behavior of a particularly interesting SU(2) gauge theory, with six massless Dirac fermions in the fundamental representation. We compute the running gauge coupling derived nonperturbatively from the Schrödinger functional of the theory, finding no evidence for an infrared fixed point up through gauge couplings g(2) of order 20. This implies that the theory either is governed in the infrared by a fixed point of considerable strength, unseen so far in nonsupersymmetric gauge theories, or breaks its global chiral symmetries producing a large number of composite Nambu-Goldstone bosons relative to the number of underlying degrees of freedom. Thus either of these phases exhibits novel behavior.

We present a novel technique for the determination of the topological susceptibility (related to the variance of the distribution of global topological charge) from lattice gauge theory simulations, based on maximum-likelihood analysis of the Markov-chain Monte Carlo time series. This technique is expected to be particularly useful in situations where relatively few tunneling events are observed. Restriction to a lattice subvolume on which topological charge is not quantized is explored, and may lead to further improvement when the global topology is poorly sampled. We test our proposed method on a set of lattice data, and compare it to traditional methods.