Register to reply

Dark photons

by wolram
Tags: dark, photons
Share this thread:
wolram
#1
Nov30-08, 09:43 AM
PF Gold
wolram's Avatar
P: 3,683
http://blogs.discovermagazine.com/co.../dark-photons/

It’s humbling to think that ordinary matter, including all of the elementary particles we’ve ever detected in laboratory experiments, only makes up about 5% of the energy density of the universe. The rest, of course, comes in the form of a dark sector: some form of energy density that can be reliably inferred through the gravitational fields it creates, but which we haven’t been able to make or touch directly ourselves.

It’s irresistible to imagine that the dark sector might be interesting. In other words, thinking like a physicist, it’s natural to wonder whether the dark sector might be complicated, with a rich phenomenology all its own. And in fact there is something interesting going on: over the last 15 years we’ve established that the dark sector comes in at least two different pieces! There is dark matter, 25% of the universe, which we know is like “matter” because it behaves that way — in particular, it clumps together under the force of gravity, and its energy density dilutes away as the universe expands. And then there is dark energy, 70% of the universe, which seems to be eerily uniform — smoothly distributed through space, and persistent (non-diluting) through time. So, there is at least that much structure in the dark sector.
Phys.Org News Partner Space news on Phys.org
Life on Mars? Implications of a newly discovered mineral-rich structure
Students see world from station crew's point of view
Exoplanet measured with remarkable precision
wolram
#2
Nov30-08, 09:48 AM
PF Gold
wolram's Avatar
P: 3,683
Is this the start of the dark ages?
wolram
#3
Nov30-08, 09:52 AM
PF Gold
wolram's Avatar
P: 3,683
http://www.sciam.com/article.cfm?id=...es-dark-matter

Magellan/U.Arizona/D.Clowe et al.
If current theories prove correct, ordinary matter—all that we can see, smell and touch—makes up just a fraction, maybe 4 percent, of the universe. The rest comes from the so-called dark sector: dark matter and dark energy, a mysterious and pervasive energy that is suspected of speeding the universe's expansion. Dark matter, so known because it refuses to emit or interact with light in a way that we can see, is nearly six times as prevalent as ordinary matter. But, for all its ubiquity, it is often tagged as being fairly bland, a sort of galactic deadweight that only reveals itself through its gravitational pull.

New theories about the hidden life of dark matter aim to shed this dull image once and for all. Whereas dark matter may not mix much with the ordinary kind, it may tango with other dark matter particles via some new force—one outside the purview of the Standard Model of particle physics.

A group of researchers at the California Institute of Technology proposes that dark matter could have its own force analogous to electromagnetism—mediated, naturally, by "dark photons". Just as in regular electromagnetism, the force would act over long ranges, and the photon (the discrete unit of light energy) would be massless. As noted by study co-author Sean Carroll, a Caltech physicist, on the blog Cosmic Variance, the theory opens the door to a rich, as yet unseen world of dark radiation, even dark magnetic and electric fields.

wolram
#4
Nov30-08, 10:16 AM
PF Gold
wolram's Avatar
P: 3,683
Dark photons

http://arxiv.org/abs/0810.0713

We propose a comprehensive theory of dark matter that explains the recent proliferation of unexpected observations in high-energy astrophysics. Cosmic ray spectra from ATIC and PAMELA require a WIMP with mass M_chi ~ 500 - 800 GeV that annihilates into leptons at a level well above that expected from a thermal relic. Signals from WMAP and EGRET reinforce this interpretation. Taken together, we argue these facts imply the presence of a GeV-scale new force in the dark sector. The long range allows a Sommerfeld enhancement to boost the annihilation cross section as required, without altering the weak scale annihilation cross section during dark matter freezeout in the early universe. If the dark matter annihilates into the new force carrier, phi, its low mass can force it to decay dominantly into leptons. If the force carrier is a non-Abelian gauge boson, the dark matter is part of a multiplet of states, and splittings between these states are naturally generated with size alpha m_phi ~ MeV, leading to the eXciting dark matter (XDM) scenario previously proposed to explain the positron annihilation in the galactic center observed by the INTEGRAL satellite. Somewhat smaller splittings would also be expected, providing a natural source for the parameters of the inelastic dark matter (iDM) explanation for the DAMA annual modulation signal. Since the Sommerfeld enhancement is most significant at low velocities, early dark matter halos at redshift ~10 potentially produce observable effects on the ionization history of the universe, and substructure is more detectable than with a conventional WIMP. Moreover, the low velocity dispersion of dwarf galaxies and Milky Way subhalos can greatly increase the substructure annihilation signal.
epenguin
#5
Nov30-08, 10:19 AM
HW Helper
epenguin's Avatar
P: 1,978
It is quite obscure.
xantox
#6
Nov30-08, 10:26 AM
PF Gold
P: 247
And of course, a dark quark could emit dark gluons, and they would carry dark colors. With the help of dark gravitons, they could be coupled as well to an N-dimensional dark spacetime.
George Jones
#7
Nov30-08, 11:18 AM
Mentor
George Jones's Avatar
P: 6,242
wolram, without using

...
,

or at least " ... ," it looks like you are commenting on the material from the links, not like you are quoting the material from the links.
wolram
#8
Nov30-08, 11:25 AM
PF Gold
wolram's Avatar
P: 3,683
Quote Quote by George Jones View Post
wolram, without using

,

or at least " ... ," it looks like you are commenting on the material from the links, not like you are quoting the material from the links.

Sorry.
Alfi
#9
Nov30-08, 11:37 AM
P: 151
the recent proliferation of unexpected observations in high-energy astrophysics.
?? there has been a recent proliferation of the unexpected. ??

ref. please.


And of course, a dark quark could emit dark gluons, and they would carry dark colors.
and the new Eighth colour. The colour on Money.


Register to reply

Related Discussions
Superb overview of contemporary research/observations in dark matter, dark energy Cosmology 0
Review of Dark Matter and Dark Energy by M. Kamionkowski Cosmology 5
Are Virtual Photons Responsible For Real Photons? Quantum Physics 11
Dark energy = dark matter*speed of light squared? Astronomy & Astrophysics 14
Dark energy redshifts cmbr photons General Physics 3