Chris Kouvaris

Towards working technicolor: Effective theories and dark matter

A fifth force, of technicolor type, responsible for breaking the electroweak theory is an intriguing extension of the standard model. Recently new theories have been shown to feature walking dynamics for a very low number of techniflavors and are not ruled out by electroweak precision measurements. We identify the light degrees of freedom and construct the associated low energy effective theories. These can be used to study signatures and relevant processes in current and future experiments. In our theory the technibaryons are pseudo Goldstone bosons and their masses arise via extended technicolor interactions. There are hypercharge assignments for the techniquarks which renders one of the technibaryons electrically neutral. We investigate the cosmological implications of this scenario and provide a component of dark matter.

Excluding Light Asymmetric Bosonic Dark Matter

We argue that current neutron star observations exclude asymmetric bosonic noninteracting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT. If bosonic weakly interacting massive particles (WIMPs) are composite of fermions, the same limits apply provided the compositeness scale is higher than ∼10¹²  GeV (for WIMP mass ∼1  GeV). In the case of repulsive self-interactions, we exclude the large range of WIMP masses and interaction cross sections which complements the constraints imposed by observations of the Bullet Cluster.

WIMP annihilation and cooling of neutron stars

We study the effect of WIMP annihilation on the temperature of a neutron star. We shall argue that the released energy due to WIMP annihilation inside the neutron stars might affect the temperature of stars older than 10x10{sup 6} years, flattening out the temperature at {approx}10{sup 4} K for a typical neutron star.

Limits on Self-Interacting Dark Matter from Neutron Stars

We impose new severe constraints on the self-interactions of fermionic asymmetric dark matter based on observations of nearby old neutron stars. Weakly interacting massive particle (WIMP) self-interactions mediated by Yukawa-type interactions can lower significantly the number of WIMPs necessary for gravitational collapse of the WIMP population accumulated in a neutron star. Even nearby neutron stars located at regions of low dark matter density can accrete a sufficient number of WIMPs that can potentially collapse, form a mini black hole, and destroy the host star. Based on this, we derive constraints on the WIMP self-interactions which in some cases are by several orders of magnitude stricter than the ones from the bullet cluster.

Boson Stars from Self-Interacting Dark Matter

A bstractWe study the possibility that self-interacting bosonic dark matter forms star-like objects. We study both the case of attractive and repulsive self-interactions, and we focus particularly in the parameter phase space where self-interactions can solve well standing problems of the collisionless dark matter paradigm. We find the mass radius relations for these dark matter bosonic stars, their density profile as well as the maximum mass they can support.

Daily modulation as a smoking gun of dark matter with significant stopping rate

We point out that for a range of parameters, the flux of DM may be stopped significantly by its interactions with the Earth. This can significantly degrade the sensitivity of direct detection experiments to DM candidates with large interactions with terrestrial nuclei. We find that a significant region of parameter space remains unconstrained for DM . a few GeV. For DM candidates with moderate levels of stopping power, the flux of DM may be blocked from below but not above a detector thereby producing a novel daily modulation. This can be explored by low threshold detectors placed on the surface or in shallow sites in the south hemisphere. Preprint: CP3-Origins-2014-019 DNRF90,DIAS-2014-19 I. INTRODUCTION At present many experimental searches use underground detectors in order to be able to detect dark matter particles, while being shielded from unwanted surface backgrounds. Most detection techniques are based on WIMP-nucleus collisions that produce su cient recoil energy to be detected either as phonons, ionization or scintillation light. However it is clear that in order to detect a WIMP it is not merely su cient to have large detector exposures, since one must also ensure that a WIMP has enough kinetic energy to produce a recoil energy above threshold. It is therefore crucial to know how much kinetic energy WIMP lose as they travel from the halo, through the Earth, and finally arrive at the detector. Obviously due to the higher density of the Earth (compared to outer space) most of the energy loss for a WIMP might take place along the distance traveling underground on the way to the detector. It is well known that Strongly Interacting Massive Particles lose enough energy to reach underground detectors with energies way below the required to trigger a signal [1, 2]. In this paper we survey the stopping force that WIMPs experience as they travel underground under a variety of assumptions for the form of the DM-nucleus interaction: electric/magnetic dipoles, light mediator exchange, and contact interactions. Previous work has studied the e ect of nuclear stopping for contact interactions [3‐ 6], and has been briefly touched upon for millicharged DM [7] and electromagnetic dipole moments [8]. We find that although these type of particles might have large enough cross sections to be easily detected in underground experiments like LUX, significant deceleration during their travel underground can invalidate this possibility simply because of their deceleration to energies below the threshold of detection. We study in detail electronic and nuclear stopping power. As we shall argue,

Decaying Dark Atom Constituents and Cosmic Positron Excess

We present a scenario where dark matter is in the form of dark atoms that can accomodate the experimentally observed excess of positrons in PAMELA and AMS-02 while being compatible with the constraints imposed on the gamma-ray flux from Fermi/LAT. This scenario assumes that the dominant component of dark matter is in the form of a bound state between a helium nucleus and a

Muon flux limits for Majorana dark matter from strong coupling theories

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Terrestrial effects on dark matter-electron scattering experiments

particle and a small component is in the form of a WIMP-like dark atom compatible with direct searches in underground detectors. One of the constituents of this WIMP-like state is a

DaMaSCUS: The Impact of Underground Scatterings on Direct Detection of Light Dark Matter

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