Modified gravity theories on a nutshell: Inflation, bounce and late-time evolution

The Next-to-Minimal Supersymmetric Standard Model

Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. No conclusive signal, despite an extensive search program that combines, often in a complementary way, direct, indirect, and collider probes, has been detected so far. This situation might change in near future due to the advent of one/multi-TON Direct Detection experiments. We thus, find it timely to provide a review of the WIMP paradigm with focus on a few models which can be probed at best by these facilities. Collider and Indirect Detection, nevertheless, will not be neglected when they represent a complementary probe.

/pdf/the-waning-of-the-wimp-a-review-of-models-searches-and-2nu358qery.pdf

The waning of the WIMP? A review of models, searches, and constraints

Dark Matter Self-interactions and Small Scale Structure

We describe the new developments in version 4 of the public computer code HiggsBounds. HiggsBounds is a tool to test models with arbitrary Higgs sectors, containing both neutral and charged Higgs bosons, against the published exclusion bounds from Higgs searches at the LEP, Tevatron and LHC experiments. From the model predictions for the Higgs masses, branching ratios, production cross sections and total decay widths—which are specified by the user in the input for the program—the code calculates the predicted signal rates for the search channels considered in the experimental data. The signal rates are compared to the expected and observed cross section limits from the Higgs searches to determine whether a point in the model parameter space is excluded at 95 % confidence level. In this paper we present a modification of the HiggsBounds main algorithm that extends the exclusion test in order to ensure that it provides useful results in the presence of one or more significant excesses in the data, corresponding to potential Higgs signals. We also describe a new method to test whether the limits from an experimental search performed under certain model assumptions can be applied to a different theoretical model. Further developments discussed here include a framework to take into account theoretical uncertainties on the Higgs mass predictions, and the possibility to obtain the $$\chi ^2$$
 likelihood of Higgs exclusion limits from LEP. Extensions to the user subroutines from earlier versions of HiggsBounds are described. The new features are demonstrated by additional example programs.

http://digital.csic.es/bitstream/10261/96281/1/LEP_tevatron_Bechtle.pdf

HiggsBounds-4: improved tests of extended Higgs sectors against exclusion bounds from LEP, the Tevatron and the LHC

Direct detection of dark matter (DM) requires an interaction of dark matter particles with nucleons. The same interaction can lead to dark matter pair production at a hadron collider, and with the addition of initial state radiation this may lead to mono-jet signals. Mono-jet searches at the Tevatron can thus place limits on DM direct detection rates. We study these bounds both in the case where there is a contact interaction between DM and the standard model and where there is a mediator kinematically accessible at the Tevatron. We find that in many cases the Tevatron provides the current best limit, particularly for light dark matter, below ∼5 GeV, a and for spin dependent interactions. Non-standard dark matter candidates are also constrained. The introduction of a light mediator significantly weakens the collider bound. A direct detection discovery that is in apparent conflict with mono-jet limits will thus point to a new light state coupling the standard model to the dark sector. Mono-jet searches with more luminosity and including the spectrum shape in the analysis can improve the constraints on DM-nucleon scattering cross section.

/pdf/the-tevatron-at-the-frontier-of-dark-matter-direct-detection-2awxz2av4r.pdf

The Tevatron at the frontier of dark matter direct detection

Direct detection of dark matter (DM) requires an interaction of dark matter particles with nucleons. The same interaction can lead to dark matter pair production at a hadron collider, and with the addition of initial state radiation this may lead to mono-jet signals. Mono-jet searches at the Tevatron can thus place limits on DM direct detection rates. We study these bounds both in the case where there is a contact interaction between DM and the standard model and where there is a mediator kinematically accessible at the Tevatron. We find that in many cases the Tevatron provides the current best limit, particularly for light dark matter, below 5 GeV, and for spin dependent interactions. Non-standard dark matter candidates are also constrained. The introduction of a light mediator significantly weakens the collider bound. A direct detection discovery that is in apparent conflict with mono-jet limits will thus point to a new light state coupling the standard model to the dark sector. Mono-jet searches with more luminosity and including the spectrum shape in the analysis can improve the constraints on DM-nucleon scattering cross section.

/pdf/the-tevatron-at-the-frontier-of-dark-matter-direct-detection-3kag86ebra.pdf

The Tevatron at the Frontier of Dark Matter Direct Detection

We analyze the existence of a dilaton in gauge theories with approximate infrared conformal symmetry. To the extent that these theories are governed in the infrared by an approximate fixed point (walking), the explicit breaking of the conformal symmetry at these scales is vanishingly small. If confinement and spontaneous chiral-symmetry breaking set in at some infrared scale, the resultant breaking of the approximate conformal symmetry can lead to the existence of a dilaton with mass parametrically small compared to the confinement scale, and potentially observable at the LHC.

Light dilaton in walking gauge theories

An unbroken discrete symmetry, analogous to $G$ parity in QCD, exists in standard model extensions with vectorlike coupling of electroweak $SU(2)$ to ``hidden sector'' fermions that are confined by a strong gauge force. For an arbitrary irreducible $SU(2)$ representation of the hidden sector fermions, the lightest hidden sector states form an isotriplet of ``pions'' with calculable mass splittings and couplings to standard model fields. The parity can be extended to fermions in real representations of color $SU(3)$, and can provide dark matter candidates with distinct collider signatures.

Weakly interacting stable hidden sector pions

We examine whether the cosmic ray positron excess observed by PAMELA can be explained by neutralino annihilation in the next-to-minimal supersymmetric standard model (NMSSM). The main dark matter annihilation products are the lightest $CP$-even scalar ${h}_{1}$ plus the lightest $CP$-odd scalar ${a}_{1}$, with the ${a}_{1}$ decaying into two muons. The energetic positrons needed to explain PAMELA are thus obtained in the NMSSM simply from kinematics. The required large annihilation cross section is obtained from an $s$-channel resonance with the heavier $CP$-odd scalar ${a}_{2}$. Various experiments constrain the PAMELA-favored NMSSM parameter space, including collider searches for a light ${a}_{1}$. These constraints point to a unique corner of the NMSSM parameter space, having a lightest neutralino mass around 160 GeV and a very light pseudoscalar mass less than a GeV. A simple parametrized formula for the charge-dependent solar modulation effects reconciles the discrepancy between the PAMELA data and the estimated background at lower energies. We also discuss the electron and gamma-ray spectra from the Fermi LAT observations, and point out the discrepancy between the NMSSM predictions and Fermi LAT preliminary results and possible resolution. An NMSSM explanation of PAMELA makes three striking and uniquely correlated predictions: the rise in the PAMELA positron spectrum will turn over at around 70 GeV, the dark matter particle mass is less than the top quark mass, and a light sub-GeV pseudoscalar will be discovered at colliders.

Yang Bai

Papers

The Tevatron at the frontier of dark matter direct detection

The Tevatron at the Frontier of Dark Matter Direct Detection

Light dilaton in walking gauge theories

Weakly interacting stable hidden sector pions

The PAMELA excess from neutralino annihilation in the NMSSM