The problem is that other similar DMP detectors (Zeplin III, CDMS 2008) with a different detection medium and higher energy thresholds see no such effect. Also, the 2-4 keV signals seen by DAMA/LIBRA are lower in energy than is theoretically predicted for DMP-nucleus collisions. Therefore, the DAMA/LIBRA result has been the subject of debate and controversy at several recent international conferences.
* * * *
As mentioned above, the other way of searching for DMPs is to look for space radiation produced when somewhere a DMP and anti-DMP annihilate. One particle expected from such annihilations is the positron, the antimatter twin of the electron. The PAMELA detector, launched on a Russian satellite by the WIZARD collaboration, has recently reported an observation of the ratio of positrons to (electrons + positrons) in the energy range 1.5 to 90 GeV. (Here, 1 GeV is 109 eV; for reference, a proton has a mass-energy of 0.938 GeV.)
The theoretical expectation is that such energetic positrons should be produced mainly in gas collisions during the propagation of cosmic ray protons in the galactic medium, and this leads to a positron ratio that should fall steeply with energy. The actual data, however, shows a strong increase in the ratio with energy, starting at a value of about 0.05 at 10 GeV and rising to above 0.15 at 90 GeV. There are similar reports of a positron excess in the 600-800 GeV range from the balloon-borne ATIC cosmic ray detector, but these seem to be in conflict with recent GLAST/Fermi results. This excess of energetic positrons is not easily explained, and could be the result of DMP-anti-DMP annihilation.
The WMAP experiment, which has mapped the cosmic microwave background with great precision, has also reported a hard microwave “haze” coming from the center of our galaxy, not readily explained by known galactic emission mechanisms. This haze could be the synchrotron radiation from energetic electrons and positrons made in DMP-anti-DMP annihilation near the galactic center. Studies there with the EGRET gamma ray detector showed an excess of gamma rays at energies above those expected from pi0 meson decays. It is suggested that the observed gamma rays might arise from the inverse Compton scattering of energetic positrons and electrons colliding with starlight and cosmic background microwaves.
Thus, from several independent sources there is evidence of energetic electrons and positrons, possibly coming from DMP-anti-DMP annihilation. On the other hand, there is no corresponding evidence of any excess of strongly interacting particles like pions and antiprotons, which would be expected from conventional matter-antimatter annihilations. In particular, the PAMELA measurements place tight limits on the antiproton content of cosmic rays, and EGRET measurements place similar limits on gamma rays from pi0 meson decays. Neither provides any indication of strongly interacting annihilation products.
These results present a paradox. If DMP-anti-DMP annihilations are producing electrons and positrons with energies of 90 GeV or more, why are these decays not making any excess of antiprotons or pi0 mesons? This is in direct conflict with expectations based on the standard model, so the observations may point to new physics beyond the standard model.
One version of such new physics has recently been suggested by Arkani-Hamed, Finkbeiner, Slatyer, and Weiner (AFSW). They propose a new “dark” force that acts only between the dark-matter particles. In this AFSW model, when there is a DMP-anti-DMP annihilation between dark matter particles that wander into each other, the particle momentarily produced in annihilation is the carrier of the new dark-matter force. And it is assumed that the force-carrier particle has a mass of around 0.1 GeV, so that its low mass constrains its subsequent decay into electron-positron pairs and/or pairs of gamma rays.
Also, because of this new force, as the particles approach each other before annihilation, an attraction due to the force occurs that increases the probability that the annihilation will occur. This is called a Sommerfeld enhancement, and it can increase the chances of annihilation by several orders of magnitude. And the AFSW model predicts that DMPs should interact primarily with heavy nuclei, giving lower recoil energies, explaining why only detectors containing iodine (like DAMA) or lead nuclei show small but detectable recoil signals.
The AFSW theory can, at the expense of postulating a new and previously unknown force, explain all of the observations described above and make predictions that can be tested by new experiments and observations. In particular, the AFSW theory predicts that, as more data is collected, the positron enhancement observed by PAMELA should continue to increase up to the highest energies that the detector can resolve (~270 GeV). As the sources of positrons become better localized in position, the theory predicts that sources of the energetic positrons should be broadly distributed rather than localized at the galactic center (e.g., at the black hole there).
When the LHC begins operation in a few months (a year late because of a major cryogenics rupture) the AFSW theory predicts observation of a striking signature of highly energetic electrons and positrons among the produced particles in the proton-proton collisions. There are also predictions for new observations from the GLAST/FERMI and HESS detectors that have recently been launched.
* * * *
What are the science-fiction implications of all this? If the picture painted by the AFSW theory is correct, the matter content of the universe is mostly dark matter with its own particles, forces, and interactions. It clusters around galaxies in a somewhat different way than do the stars and planets of normal matter, and it may have complexities and structures that we have not imagined. Are there the equivalent of atoms and molecules made of dark matter that are invisible to us except through their gravitational interactions? There are almost no antiprotons in our galactic neighborhood, but apparently there is plenty of dark matter and antimatter. Can we find chunks of dark matter and dark antimatter and annihilate them for energy and propulsion?
So there may be another force in the universe, a fifth “dark” force that acts only between “dark” particles that ignore us as we ignore them, passing invisibly through our stars and planets as if they were not there.
The surface has just been scratched in this area. For science fiction this has the makings of new kinds of energy sources and propulsion, and perhaps even a new “dark’ territory to be explored by space travelers.
Copyright © 2009 John G. Cramer
* * * *
AV Columns Online: Electronic reprints of over 145 “The Alternate View” columns by John G. Cramer, previously published in Analog, are available online at: www.npl.washington.edu/av.
The AFSW Theory:
N. Arkani-Hamed, D. P. Finkbeiner, T. R. Slatyer, and N. Weiner, “A Theory of Dark matter,” Physical Review D79, 015014 (2009), arXiv preprint 0810.0713v3 [hep-ph].
[Back to Table of Contents]
Short Story: THE UNIVERSE BENEATH OUR FEET by Carl Frederick
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Illustration by John Allemand
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How you see the world depends on how you look at it....
* * * *
he disturbance in the ice perturbed the funeral.
Despite the grinding sounds from the ice beneath, Jerik chirped his attention on Harshket, the High Priest of the People of the Rippling Wall. The priest, four feet planted firmly on the ice, raised his other two to heaven and commended the recently deceased Master of the Fourth School to the Great God, the god of water, the god of good.
A few feet in front of the priest, that Master of the Fourth School, his life-bubbles still pressing him to the ice, lay motionless. On a circle centered on the priest, six of the people, the Beaters to Heaven, stood at the six points of the compass. And behind them, outside another circle, waited the mass of the people—including Jerik. Though he listened to the priest's words (he could hardly do otherwise), he ping-chirped very little; he didn't really care to register the details of the priest's movements. And standing behind Jerik, his friend K'chir ping-chirped not at all. Jerik could hear the tapping as K'chir sequentially raised and lowered his feet in obvious boredom. The Master of the Fo
urth had been K'chir's master. Jerik knew the two didn't like each other and K'chir wasn't exactly crushed at the loss. Jerik sighed. He was still only in Third School. All he could do was hope.
At length, the priest lowered all six of his legs to the ice and addressed the inner circle. “Beaters,” he intoned, “do your sacred duty. Drive the god-given life-bubbles from the deceased. Beat him well and true, and enable him to rise swiftly to join the Great God of the Water. Let the deceased rise far from the evils of the world and from the evil presence of the God of the Ice."
"Finally!” whispered K'chir. “I thought Harshket would never stop babbling."
Those standing in the inner circle clattered somberly to the corpse. Each raised two forward legs above the body and, at a chirp from the priest, brought them down and began pummeling the ex-Master of the Fourth.
A trickle of bubbles dribbled from the master's mouth and collected in a clutch on the ice. Additional life-bubbles, tiny but numerous, shook free from the master's body and leg fur, carpeting the ice and softening the ping echoes.
Ping-chirping steadily now, Jerik observed the beating. He was surprised how few life-bubbles the master had possessed. But then again, the master was very old. And for the most part, vitality equated to how strong one's contact with the ice was—and that depended on one's supply of bubbles. A shift of the current brought Jerik the scent of the corpse—a terrible smell of death. Jerik blew out water in revulsion.
The priest gave a sharp chirp and the Beaters to Heaven moved back, causing the corpse, lighter without its bubbles, to twitch in the current. All was quiet, except for a susurrus of respectful chirping—and the constant grinding from the ice. Jerik could tell from his pings that many of the people resented the grinding and groaning from below. He knew though, that K'chir was far from annoyed; he was excited that there might actually be a release from the constant boredom.
Very slowly, the Master of the Fourth began to rise.
Ping-chirping in respect, Jerik observed the body rising faster, gently twisting and rolling in the current. Jerik breathed in relief as the death smell faded.
Jerik added to the wall of sound as the people, as a whole, ping-chirped the deceased, following the body to heaven with their chirps. As the body progressed steadily higher, the chirp echoes grew ever more faint, until they ceased altogether—until all that remained of the Master of the Fourth was a thin lake of air on the ice, the merged totality of the master's life-bubbles.
"Well, that's over,” K'chir whispered from behind.
"Not quite over,” said Jerik.
The circle of mourners converged on the lake of air. In order of their seniority, the High Priest Harshket going first, they wallowed in the air, trapping minuscule bubbles onto their leg fur. The lake shrank until, when K'chir's turn came, there was no air left at all.
Jerik chuckled. “It's too bad, K'chir,” he said. “It would have been really funny if you'd been able to absorb some of your master's essence—considering how much you hated him."
"I don't believe in that essence nonsense,” said K'chir, turning away from the one-time air-lake. He tapped a leg in disgust. “But the air was certainly full of the master's scent. I'll survive just fine without it.” He chirped a smile. “It's air. Life-giving air, certainly, but that's all."
"It's God's gift,” said Jerik.
"Come on!” said K'chir. “I don't believe in any such god."
Jerik winced. He didn't believe either, or at least didn't think he believed, but saying so aloud was not wise.
"Let's get out of here,” said K'chir. He and Jerik began to glide away, but the High Priest held up two legs.
"K'chir. Please wait until the others leave.” The priest spoke in a voice that was threatening despite the courtesy. “I want to talk to you."
K'chir stopped, but Jerik, as quietly and unobtrusively as he could, continued to glide away.
"And you,” said the priest. “Jerik, by your smell."
Jerik stopped abruptly. “Yes, sir?"
"Stay!"
"Yes, sir.” Jerik glided back to Harshket. He waited nervously with K'chir as the chirps from the people faded away. Then Harshket, without preamble, said, “K'chir. Do you know the Six-fold Way?"
"Of course, I do. Every First School student learns it on the first—"
"Recite it,” Harshket demanded.
"Why?"
"Recite it. Now!"
Jerik heard K'chir tap a leg in a quiet shrug.
"All right,” said K'chir in a voice at the border between polite and put upon. “The qualities of the People of the Rippled Wall are: Obedience.” He stamped his front left leg to the ice as custom required. “Loyalty.” He stamped his front right leg. “Honesty. Knowledge. Wisdom.” At the mention of each quality, he stamped another leg. “And Reverence,” he intoned, stamping his sixth foot.
"Do you think you exemplify these sacred qualities?” said Harshket.
K'chir stood silent.
"From your comments that I and no doubt many others of the people heard,” said Harshket, “I rather think you fail with regard to Reverence, the highest of the qualities."
"I'm not sure I am fully a believer,” said K'chir. Jerik noticed that his friend was being a lot more tentative than usual.
"Not sure?” Harshket raised his forward legs in the air and chirped, the rasping chirp of the elderly. “Can you not detect the sweet manna sent down from heaven by our kind and all-powerful god?"
"Maybe...” said K'chir in a cautious, even frightened voice. “Maybe the manna from heaven is just the dead—decomposed and sent back down to us."
"Nonsense!"
Jerik felt the turbulence of the current reflecting Harshket's anger—and then the turbulence subsided.
"Who, K'chir, do you think does the sending?” Harshket spoke in the voice of a philosophy master, which, of course, he was.
"The same one who sends down those,” said K'chir. He pinged a stream of sulfur-bubbles coming from on high. “And why would God send down foul-smelling, inedible life-bubbles that burn our bodies?"
"To test our faith, of course. You know that.” Harshket spoke as if he were addressing young children.
Jerik moved his mandible in a soft, unpingable show of amusement. Of course, to old Harshket, everyone was surely a child.
"You are in Fourth School—Collective philosophy,” said Harshket, wearily. “Collective! Do you think you're setting a good example for your young friend who is only, if I recall correctly, in Third School—Deductive philosophy?"
"I think, sir, I am setting a good example. At least I'm trying to."
"Then you fall short in the quality of Wisdom as well."
Jerik sensed his friend bristle.
"Yes, I accept the Six-fold way,” said K'chir. “But there are qualities it leaves out. What about Innovation? What about Adventurousness?” He chirped a sigh. “I'm so bored."
"Ah, so that's it.” Harshket chuckled and Jerik breathed easier. He'd been worried his friend had been pushing the priest too far.
"Adventurousness,” said Harshket, thoughtfully. “We have ice-gliding races, wrestling, debate rallies. Compete! That should address your boredom. Or perhaps you might study harder."
"I'm bored with all our rituals and traditions,” said K'chir. “I want to create, to innovate."
"Me too,” said Jerik, wanting to get into the game, now that High Priest Harshket seemed more disputative than angry.
"You are a mere juvenile, Jerik!” said Harshket, in a voice near anger. “And so young that your voice is almost as high pitched as your ping-chirp."
"Yes, sir.” Jerik thought deference the safest course at the moment.
Harshket chirped a sigh. “And as to you, K'chir. You must wait until the Sixth School—Transcendental philosophy. Your time will come."
"Maybe our culture has gotten too old.” K'chir lowered his head and soft-pinged the ice in an expression of sadness. “During our creative period, when we should be
advancing the art, we're still learning what has gone before—studying philosophy, memorizing poetry.” He chirped frustration. “And even then, we study narrower and narrower specialties until we cannot any longer see the whole. True innovation is impossible."
"That is known,” said Harshket. “It is a sign that God's work for his people is almost done."
Jerik was afraid that would set his friend off, would make him say something he'd regret. But K'chir merely said, “I want more in life."
"More?” Now Harshket sounded angry. “Just what do you young people want?"
"For one thing,” said K'chir, “true knowledge."
"Meaning what?"
"Well...” said K'chir in a light tone. He'd apparently also detected the edge in Harshket's voice and knew it could mean danger. K'chir pinged the ice. “I'd sort of like to know what that grinding beneath the ice is."
Clearly, K'chir was trying to lighten the mood.
"Things have come up through the ice before.” Harshket's voice sounded troubled.
"They have?” said K'chir in a curious tone with no trace of challenge.
"You will learn about it in Fifth School next year."
"Please, sir,” said K'chir, “would you tell me about it now?"
Harshket made a throaty chirp toward the ice and said, “It happened many great-tides ago.” He spoke in a distant voice. “This thing came up through a fissure—a crack in the ice after a heaven-quake. And the thing came into the world upside-down. It had four feet rather than six. The feet pointed heavenward—a clear sign that it came from the God of Evil and Ice."
Harshket chirp-mapped the thing slowly and in exquisite detail. It took Jerik's breath away. The thing from the fissure had thin legs, rodlike with pads for feet. And it had a body with more rods sticking out nonsymmetrically from all sides. It seemed alive: a small shell-like object on its head swiveled back and forth, and it virtually reeked with frenzied electromagnetic waves. All this did Harshket transmit through a chirp-map, crisp and precise as if the priest had only encountered the object at last tide.
Analog SFF, December 2009 Page 8
