TASI 2009 Lectures: Searching for Unexpected Physics at the LHC

These TASI lectures consider low mass hidden sectors from Hidden Valleys, Quirks and Unparticles. We show how each corresponds to a different limit of the same class of models: hidden sectors with non-abelian gauge groups with mass gaps well below a TeV that communicate to the Standard Model through weak scale suppressed higher dimension operators. We provide concrete examples of such models and discuss LHC signatures. Lastly we turn to discussing the application of Hidden Valleys to dark matter sectors.Comment: 35 pages, 21 figure

Multi-Component Dark Matter

We explore multi-component dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multi-component nature of the dark matter naturally arises in supersymmetric models, where both R parity and an additional symmetry, such as a $Z_2$, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA, ATIC and synchrotron signals, without an excess in antiprotons which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.Comment: 4 pages, no figures. v2: paper shortened to letter length; modified dark matter spectru

Quantum Darwinism requires an extra-theoretical assumption of encoding redundancy

Observers restricted to the observation of pointer states of apparatus cannot conclusively demonstrate that the pointer of an apparatus A registers the state of a system of interest S without perturbing S. Observers cannot, therefore, conclusively demonstrate that the states of a system S are redundantly encoded by pointer states of multiple independent apparatus without destroying the redundancy of encoding. The redundancy of encoding required by quantum Darwinism must, therefore, be assumed from outside the quantum-mechanical formalism and without the possibility of experimental demonstration.Comment: 5 pages, 1 figure. Comments on foundational assumptions of W. Zurek (2009) Nat Phys 5 181 (arXiv 0903.5082). v2 significant revision to improve clarit

A Natural Supersymmetric Model with MeV Dark Matter

It has previously been proposed that annihilating dark matter particles with MeV-scale masses could be responsible for the flux of 511 keV photons observed from the region of the Galactic Bulge. The conventional wisdom, however, is that it is very challenging to construct a viable particle physics model containing MeV dark matter. In this letter, we challenge this conclusion by describing a simple and natural supersymmetric model in which the lightest supersymmetric particle naturally has a MeV-scale mass and the other phenomenological properties required to generate the 511 keV emission. In particular, the small ($\sim$ $10^{-5}$) effective couplings between dark matter and the Standard Model fermions required in this scenario naturally lead to radiative corrections that generate MeV-scale masses for both the dark matter candidate and the mediator particle.Comment: 4 pages, 1 figure. v2: Small modification to discussion of spectru

Darkogenesis

In standard models of baryogenesis and of dark matter, the mechanisms which generate the densities in both sectors are unrelated to each other. In this paper we explore models which generate the baryon asymmetry through the dark matter sector, simultaneously relating the baryon asymmetry to the dark matter density. In the class of models we explore, a dark matter asymmetry is generated in the hidden sector through a first order phase transition. Within the hidden sector, it is easy to achieve a sufficiently strong first order phase transition and large enough $CP$ violation to generate the observed asymmetry. This can happen above or below the electroweak phase transition, but in both cases significantly before the dark matter becomes non-relativistic. We study examples where the Asymmetric Dark Matter density is then transferred to the baryons both through perturbative and non-perturbative communication mechanisms, and show that in both cases cosmological constraints are satisfied while a sufficient baryon asymmetry can be generated.Comment: 20 pages, 2 figure

Topological Schr\"odinger cats: Non-local quantum superpositions of topological defects

Topological defects (such as monopoles, vortex lines, or domain walls) mark locations where disparate choices of a broken symmetry vacuum elsewhere in the system lead to irreconcilable differences. They are energetically costly (the energy density in their core reaches that of the prior symmetric vacuum) but topologically stable (the whole manifold would have to be rearranged to get rid of the defect). We show how, in a paradigmatic model of a quantum phase transition, a topological defect can be put in a non-local superposition, so that - in a region large compared to the size of its core - the order parameter of the system is "undecided" by being in a quantum superposition of conflicting choices of the broken symmetry. We demonstrate how to exhibit such a "Schr\"odinger kink" by devising a version of a double-slit experiment suitable for topological defects. Coherence detectable in such experiments will be suppressed as a consequence of interaction with the environment. We analyze environment-induced decoherence and discuss its role in symmetry breaking.Comment: 7 pages, 4 figure

On the Effect of Nuclear Response Functions in Dark Matter Direct Detection

We examine the effect of nuclear response functions, as laid out in [Fitzpatrick et al, arXiv:1203.3542], on dark matter (DM) direct detection in the context of well-motivated UV completions, including electric and magnetic dipoles, anapole, spin-orbit, and pseudoscalar-mediated DM. Together, these encompass five of the six nuclear responses extracted from the non-relativistic effective theory of [Fitzpatrick et al, arXiv:1203.3542] (with the sixth difficult to UV complete), with two of the six combinations corresponding to standard spin-independent and -dependent responses. For constraints from existing direct detection experiments, we find that only the COUPP constraint, due to its heavy iodine target with large angular momentum and an unpaired spin, and its large energy range sensitivity, is substantially modified by the new responses compared to what would be inferred using the standard form factors to model the energy dependence of the response. For heavy targets such as xenon and germanium, the behavior of the new nuclear responses as recoil energy increases can be substantially different than that of the standard responses, but this has almost no impact on the constraints derived from experiments such as LUX, XENON100 and CDMS since the maximum nuclear recoil energy detected in these experiments is relatively low. We simulate mock data for 80 and 250 GeV DM candidates utilizing the new nuclear responses to highlight how they might affect a putative signal, and find the new responses are most important for momentum-suppressed interactions such as the magnetic dipole or pseudoscalar-mediated interaction when the target is relatively heavy (such as xenon and iodine).Comment: 42 pages, 12 figures, 5 table

Asymmetric Dark Stars and Neutron Star Stability

We consider gravitationally bound states of asymmetric dark matter (ADM stars), and the impact of ADM capture on the stability of neutron stars. We derive and interpret the equation of state for ADM with both attractive and repulsive interactions, and solve the Tolman-Oppenheimer-Volkoff equations to find equilibrium sequences and maximum masses of ADM stars. Gravitational wave searches can utilize our solutions to model exotic compact objects (ECOs). Our results for attractive interactions differ substantially from those in the literature, where fermionic ADM with attractive self-interactions was employed to destabilize neutron stars more effectively than non-interacting fermionic ADM. By contrast, we argue that fermionic ADM with an attractive force is no more effective in destabilizing neutron stars than fermionic ADM with no self-interactions.Comment: 9 pages plus 2 appendices (15 pages total), 7 figures, 1 tabl

Flavor and Collider Signatures of Asymmetric Dark Matter

We consider flavor constraints on, and collider signatures of, Asymmetric Dark Matter (ADM) via higher dimension operators. In the supersymmetric models we consider, R-parity violating (RPV) operators carrying B-L interact with n dark matter (DM) particles X through an interaction of the form W = X^n O_{B-L}, where O_{B-L} = q l d^c, u^c d^c d^c, l l e^c. This interaction ensures that the lightest ordinary supersymmetric particle (LOSP) is unstable to decay into the X sector, leading to a higher multiplicity of final state particles and reduced missing energy at a collider. Flavor-violating processes place constraints on the scale of the higher dimension operator, impacting whether the LOSP decays promptly. While the strongest limitations on RPV from n-\bar{n} oscillations and proton decay do not apply to ADM, we analyze the constraints from meson mixing, mu-e conversion, mu -> 3 e and b -> s l^+ l^-. We show that these flavor constraints, even in the absence of flavor symmetries, allow parameter space for prompt decay to the X sector, with additional jets and leptons in exotic flavor combinations. We study the constraints from existing 8 TeV LHC SUSY searches with (i) 2-6 jets plus missing energy, and (ii) 1-2 leptons, 3-6 jets plus missing energy, comparing the constraints on ADM-extended supersymmetry with the usual supersymmetric simplified models.Comment: 63 pages, 26 figures, 10 tables, revtex

What is "system": some decoherence-theory arguments

We discuss the possibility of making the {\it initial} definitions of mutually different (possibly interacting, or even entangled) systems in the context of decoherence theory. We point out relativity of the concept of elementary physical system as well as point out complementarity of the different possible divisions of a composite system into "subsystems", thus eventually sharpening the issue of 'what is system'.Comment: 9 pages, no figure