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Katherine Freese

Publications and source records attributed to Katherine Freese.

At least 145 records · Page 8Linked to original sources
arXiv2009

Compatibility of DAMA/LIBRA dark matter detection with other searches in light of new Galactic rotation velocity measurements

The DAMA/NaI and DAMA/LIBRA annual modulation data, which may be interpreted as a signal for the existence of weakly interacting dark matter (WIMPs) in our galactic halo, are re-examined in light of new measurements of the local velocity relative to the galactic halo. In the vicinity of the Sun, the velocity of the Galactic disk has been estimated to be 250 km/s rather than 220 km/s. Our analysis is performed both with and without the channeling effect included. The best fit regions to the DAMA data are shown to move to slightly lower WIMP masses. Compatibility of DAMA data with null results from other experiments (CDMS, XENON10, and CRESST I) is investigated given these new velocities. A small region of spin-independent (elastic) scattering for 7-8 GeV WIMP masses remains at 3$σ$. Spin-dependent scattering off of protons is viable for 5-15 GeV WIMP masses for direct detection experiments (but has been argued by others to be further constrained by Super-Kamiokande due to annihilation in the Sun).

astro-ph.CO↗
arXiv2009

Is the Carter-Israel conjecture correct?

According to the Carter-Israel conjecture, the end-state of the gravitational collapse of matter is a Kerr-Newman black hole. Nevertheless, neither the theory nor observations can confirm that. In this talk, we discuss the possibility that the collapsing matter can create a super-spinning compact object with no event horizon, and we show how near future observations at sub-millimeter wavelength of SgrA* can test this scenario for the black hole candidate in the Galactic Center.

astro-ph.HE↗
arXiv2009

Are we seeing the beginnings of Inflation?

Phantom Cosmology provides an unique opportunity to "connect" the phantom driven (low en- ergy meV scale) dark energy phase to the (high energy GUT scale) inflationary era. This is possible because the energy density increases in phantom cosmology. We present a concrete model where the energy density, but not the scale factor, cycles through phases of standard radiation/matter domi- nation followed by dark energy/inflationary phases, and the pattern repeating itself. An interesting feature of the model is that once we include interactions between the "phantom fluid" and ordinary matter, the Big rip singularity is avoided with the phantom phase naturally giving way to a near exponential inflationary expansion.

astro-ph.CO↗
arXiv2009

Kaluza-Klein Dark Matter And Neutrinos From Annihilation In The Sun

In models with one universal extra dimension (UED), the first Kaluza-Klein excitations of the hypercharge gauge boson, B^(1), and the neutral component of isospin gauge boson, W^3(1), are each viable dark matter candidates. In either case, such particles are predicted to accumulate in the core of the Sun, where they annihilate to generate a potentially observable flux of high energy neutrinos. In this article, we calculate the flux of neutrinos produced in this model and determine the constraints that can be placed on the UED parameter space from current IceCube data. For the case of B^(1) dark matter, we find that the present limits from IceCube are stronger than those from direct dark matter detection experiments such as CDMS and XENON10. For W^3(1) dark matter, the present IceCube data provides a constraint slightly weaker than direct detection experiments. In addition, we also present the projected regions of UED parameter space that can be probed by IceCube/DeepCore in the near future and compare them to the prospects for future direct detection experiments.

hep-ph↗
arXiv2009

High-Energy Neutrino Signatures of Dark Matter Decaying into Leptons

Decaying dark matter has previously been proposed as a possible explanation for the excess high energy cosmic ray electrons and positrons seen by PAMELA and the Fermi Gamma-Ray Space Telescope (FGST). To accommodate these signals however, the decays must be predominantly leptonic, to muons or taus, and therefore produce neutrinos, potentially detectable with the IceCube neutrino observatory. We find that, with five years of data, IceCube (supplemented by DeepCore) will be able to significantly constrain the relevant parameter space of decaying dark matter, and may even be capable of discovering dark matter decaying in the halo of the Milky Way.

astro-ph.HE↗
arXiv2009

Implications of primordial black holes on the first stars and the origin of the super--massive black holes

If the cosmological dark matter has a component made of small primordial black holes, they may have a significant impact on the physics of the first stars and on the subsequent formation of massive black holes. Primordial black holes would be adiabatically contracted into these stars and then would sink to the stellar center by dynamical friction, creating a larger black hole which may quickly swallow the whole star. If these primordial black holes are heavier than $\sim 10^{22} {\rm g}$, the first stars would likely live only for a very short time and would not contribute much to the reionization of the universe. They would instead become $10 - 10^3 M_\odot$ black holes which (depending on subsequent accretion) could serve as seeds for the super--massive black holes seen at high redshifts as well as those inside galaxies today.

astro-ph↗
arXiv2009

Constraints on dark matter particles charged under a hidden gauge group from primordial black holes

In order to accommodate increasingly tighter observational constraints on dark matter, several models have been proposed recently in which dark matter particles are charged under some hidden gauge group. Hidden gauge charges are invisible for the standard model particles, hence such scenarios are very difficult to constrain directly. However black holes are sensitive to all gauge charges, whether they belong to the standard model or not. Here, we examine the constraints on the possible values of the dark matter particle mass and hidden gauge charge from the evolution of primordial black holes. We find that the existence of the primordial black holes with reasonable mass is incompatible with dark matter particles whose charge to mass ratio is of the order of one. For dark matter particles whose charge to mass ratio is much less than one, we are able to exclude only heavy dark matter in the mass range of 10^(11) GeV - 10^(16) GeV. Finally, for dark matter particles whose charge to mass ratio is much greater than one, there are no useful limits coming from primordial black holes.

hep-ph↗
arXiv2009

High Energy Neutrinos As A Test of Leptophilic Dark Matter

Recently, observations by PAMELA, the Fermi Gamma Ray Space Telescope, and other cosmic ray experiments have generated a great deal of interest in dark matter (DM) particles which annihilate at a high rate to leptons. In this letter, we explore the possibility of using large volume neutrino telescopes, such as IceCube, to constrain such models; specifically we consider signals due to DM annihilation in the inner Milky Way. We find that, if Dark Matter annihilations are responsible for the signals observed by PAMELA and FGST, then IceCube (in conjunction with the planned low threshold extension, DeepCore) should detect or exclude the corresponding neutrino signal from the inner Milky Way with a few years of observation.

astro-ph.CO↗
arXiv2009

Dark Stars: a new look at the First Stars in the Universe

We have proposed that the first phase of stellar evolution in the history of the Universe may be Dark Stars (DS), powered by dark matter heating rather than by nuclear fusion, and in this paper we examine the history of these DS. The power source is annihilation of Weakly Interacting Massive Particles (WIMPs) which are their own antiparticles. These WIMPs are the best motivated dark matter (DM) candidates and may be discovered by ongoing direct or indirect detection searches (e.g. FERMI /GLAST) or at the Large Hadron Collider at CERN. A new stellar phase results, powered by DM annihilation as long as there is DM fuel, from millions to billions of years. We build up the dark stars from the time DM heating becomes the dominant power source, accreting more and more matter onto them. We have included many new effects in the current study, including a variety of particle masses and accretion rates, nuclear burning, feedback mechanisms, and possible repopulation of DM density due to capture. Remarkably, we find that in all these cases, we obtain the same result: the first stars are very large, 500-1000 times as massive as the Sun; as well as puffy (radii 1-10 A.U.), bright ($10^6-10^7 L_\odot$), and cool ($T_{surf} < $10,000 K) during the accretion. These results differ markedly from the standard picture in the absence of DM heating. Hence DS should be observationally distinct from standard Pop III stars. In addition, DS avoid the (unobserved) element enrichment produced by the standard first stars. Once the dark matter fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for the supermassive black holes and intermediate black holes, and explain ARCADE data.

astro-ph.CO↗
arXiv2009

Dark Stars: A New Study of the FIrst Stars in the Universe

We have proposed that the first phase of stellar evolution in the history of the Universe may be Dark Stars (DS), powered by dark matter heating rather than by nuclear fusion. Weakly Interacting Massive Particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a Dark Star, powered by dark matter annihilation as long as there is dark matter fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright ($\sim 10^6 L_\odot$) and cool ($T_{surf} < 10,000$K) during the DS phase, and grow to be very massive (500-1000 times as massive as the Sun). These results differ markedly from the standard picture in the absence of DM heating, in which the maximum mass is about 140$M_\odot$ and the temperatures are much hotter ($T_{surf} > 50,000$K); hence DS should be observationally distinct from standard Pop III stars. Once the dark matter fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.

astro-ph.CO↗
arXiv2009

Apparent shape of super-spinning black holes

We consider the possibility that astrophysical Black Holes (BHs) can violate the Kerr bound; i.e., they can have angular momentum greater than BH mass, $J > M$. We discuss implications on the BH apparent shape. Even if the bound is violated by a small amount, the shadow cast by the BH changes significantly (it is $\sim$ an order of magnitude smaller) from the case with $J \le M$ and can be used as a clear observational signature in the search for super--spinning BHs. We discuss briefly recent observations in the mm range of the super--massive BH at the Center of the Galaxy, speculating on the possibility that it might violate the Kerr bound.

astro-ph↗
arXiv2009

Dark Stars: Död och Återuppståndelse

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the previous contribution present the story of Dark Stars. In this second part, we describe the structure of Dark Stars and predict that they are very massive ($\sim 800 M_\odot$), cool (6000 K), bright ($\sim 10^6 L_\odot$), long-lived ($\sim 10^6$ years), and probable precursors to (otherwise unexplained) supermassive black holes. Later, once the initial dark matter fuel runs out and fusion sets in, dark matter annihilation can predominate again if the scattering cross section is strong enough, so that a Dark Star is born again.

astro-ph.CO↗
arXiv2009

Dark Stars: Begynnelsen

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the following contribution present the story of Dark Stars. In this first part, we describe the conditions under which dark stars form in the early universe: 1) high dark matter densities, 2) the annihilation products get stuck inside the star, and 3) dark matter heating wins over all other cooling or heating mechanisms.

astro-ph.CO↗
arXiv2009

Compatibility of DAMA/LIBRA dark matter detection with other searches

The DAMA/NaI and DAMA/LIBRA annual modulation data, which may be interpreted as a signal for the existence of weakly interacting dark matter (WIMPs) in our galactic halo, are examined in light of null results from other experiments. We use the energy spectrum of the combined DAMA modulation data given in 36 bins, and include the effect of channeling. Several statistical tools are implemented in our study: likelihood ratio with a global fit and with raster scans in the WIMP mass and goodness-of-fit (g.o.f.). These approaches allow us to differentiate between the preferred (global best fit) and allowed (g.o.f.) parameter regions. It is hard to find WIMP masses and couplings consistent with all existing data sets. For spin-independent (SI) interactions, the best fit DAMA regions are ruled out to the 3$σ$ C.L., even with channeling taken into account. However, for WIMP masses of ~8 GeV some parameters outside these regions still yield a moderately reasonable fit to the DAMA data and are compatible with all 90% C.L. upper limits from negative searches, when channeling is included. For spin-dependent (SD) interactions with proton-only couplings, a range of masses below 10 GeV is compatible with DAMA and other experiments, with and without channeling, when SuperK indirect detection constraints are included; without the SuperK constraints, masses as high as ~20 GeV are compatible. For SD neutron-only couplings we find no parameters compatible with all the experiments. Mixed SD couplings are examined: e.g. ~8 GeV mass WIMPs with a_n = +/- a_p are found to be consistent with all experiments. In short, there are surviving regions at low mass for both SI and SD interactions; if indirect detection limits are relaxed, some SD proton-only couplings at high masses also survive.

astro-ph↗
arXiv2008

Dark Stars: the First Stars in the Universe may be powered by Dark Matter Heating

A new line of research on Dark Stars is reviewed, which suggests that the first stars to exist in the universe were powered by dark matter heating rather than by fusion. Weakly Interacting Massive Particles, which may be there own antipartmers, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a Dark Star, powered by dark matter annihilation as long as there is dark matter fuel.

astro-ph↗
arXiv2008

Review of Observational Evidence for Dark Matter in the Universe and in upcoming searches for Dark Stars

Over the past decade, a consensus picture has emerged in which roughly a quarter of the universe consists of dark matter. The observational evidence for the existence of dark matter is reviewed: rotation curves of galaxies, weak lensing measurements, hot gas in clusters, primordial nucleosynthesis and microwave background experiments. In addition, a new line of research on Dark Stars is presented, which suggests that the first stars to exist in the universe were powered by dark matter heating rather than by fusion: the observational possibilities of discovering dark matter in this way are discussed.

astro-ph↗
arXiv2008

Gravity Waves from Chain Inflation

Chain inflation proceeds through a series of first order phase transitions, which can release considerable gravitational waves (GW). We demonstrate that bubble collisions can leave an observable signature for future high-frequency probes of GWs, such as advanced LIGO, LISA and BBO. A "smoking gun" for chain inflation would be wiggles in the spectrum (and consequently in the tensor spectral index) due to the multiple phase transitions. The spectrum could also be distinguished from a single first order phase transition by a small difference in the amplitude at low frequency. A second origin of GWs in chain inflation are tensor modes from quantum fluctuations; these GW can dominate and be observed on large scales. The consistency relation between scalar and tensor modes is different for chain inflation than for standard rolling models and is testable by Cosmic Microwave Background experiments. If inflation happened through a series of rapid tunnelings in the string landscape, future high frequency probes of GW can shed light on the structure of the landscape.

hep-th↗