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Weird ‘unparticle’ boosted by Tevatron signal
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Kate McAlpine
predicted by the standard model. Two separate groups now suggest an explanation for this larger asymmetry lies in the unparticle, a hypothetical entity conjured up in 2007 by theorist Howard Georgi of Harvard University. Georgi suggested that a property known as scale invariance – seen in fractal-like patterns that remain unchanged even when you zoom in and out to
ELASTIC “unparticles” could explain a mysterious signal glimpsed at a particle collider a year ago. That would link a tenuous but intriguing idea to one of the biggest mysteries in physics: why matter prevails over antimatter in the universe. “I think this will increase the unparticle’s credibility as a theory,” says Run-Hui Li of Yonsei University in Seoul, South Korea, “Their charge and spin would be fixed but their the leader of one of two teams mass would vary depending proposing the link. on the viewing scale” Matter and antimatter are thought to have been created in equal amounts after the big bang, different scales, like the branching of redwood trees and the jagged yet something has caused matter edges of coastlines – could apply to be far more dominant than to individual particles too. The antimatter, at least in our patch charge and spin of unparticles of the universe. would be fixed but, counterA possible explanation is that intuitively, their mass would some physical processes favour somehow vary depending on the matter. For example, according scale at which an observer viewed to the standard model of particle the particle. physics, particles known as Such unparticles could play B mesons constantly switch, a role in a popular proposed or mix, between their matter and antimatter forms. Because it is slightly easier for an anti-B meson to become a normal B meson than vice versa, an imbalance accrues. This “uneven mixing” gets transferred to the particles produced when B mesons decay, but alone is not big enough to explain the observed matterantimatter asymmetry. Previously, several teams have glimpsed examples of asymmetry even larger than the standard model predicts. In May 2010, researchers at the Fermi National Accelerator Laboratory in Batavia, Illinois, reported a 1 per cent preference for the number of B mesons produced in their particle smasher, the Tevatron (arxiv.org/ abs/1005.2757). This is 40 times larger than the imbalance
Do gut problems set the brain up for depression?
EARLY digestive problems may hardwire the brain for depression. While gut problems are often linked with depression, they are generally assumed to arise from hormones released because of alterations in mood. Pankaj Pasricha and colleagues at Stanford University in California believe it might be the other way round. Pasricha’s team gave young rats a mild stomach irritant, then tested them for symptoms of depression at 10 weeks old. The rats showed more signs of depression and higher levels of stress hormones in the brain than healthy rats. Jamming signals from nerves in the gut made no difference to their depression, suggesting that ongoing gut pain wasn’t the trigger. Blocking receptors to stress hormones in the brain did alleviate the effects (PLoS One, DOI: 10.1371/journal. pone.0019498). Next Pasricha wants to explore the role of the vagus nerve, which allows the gut to communicate with the brain. Some people are more susceptible to depression than others, however. Understanding genes involved in the disorder could help to explain why. Gerome Breen at King’s College London and colleagues found strong evidence of a genetic link in cases of severe depression. They scanned the genomes of individuals from over 800 families with a history of depression. The results highlight abnormal variations in genes on chromosome 3 (American Journal of Psychiatry, DOI: 10.1176/appi.ajp.2011.10091342). A group from Washington University in St Louis, Missouri, came to the same conclusion – the first time such a finding has been replicated. Understanding which pathways may be affected by these variations, could help personalise medicine. At the moment only half of the people given medication for depression –Do B mesons hold the answer?– respond at all. Catherine de Lange n FERMILAB/SCIENCE PHOTO LIBRARY
‘Unparticle’ boosted by Tevatron signal
extension to the standard model, known as supersymmetry. Xiao-Gang He and his colleagues at Shanghai Jiao Tong University in China calculate that unparticles might also affect the lifetimes of B mesons. That is because quantum mechanics dictates that if they exist, “virtual” versions must exist too. Such transient unparticles would pop in and out of existence and could sometimes affect the lifetimes of real B mesons. And if this influence differed between the B meson and its antimatter counterpart, it could enhance the already uneven mixing predicted by the standard model enough to account for the mysterious Tevatron signal (Journal of Physics Letters B, DOI: 10.1016/j.physletb.2011.03.001). The unparticle’s elastic mass means it could conceivably have avoided detection in the Tevatron until now. A separate group led by Li has come to a similar conclusion (arxiv.org/abs/1012.0095). Bruce Hoeneisen, a member of the Fermilab team that saw the B meson imbalance in 2010, says other options, including new types of quarks not currently included in the standard model, could explain the Tevatron signal. He also cautions that the Tevatron finding requires confirmation. n
21 May 2011 | NewScientist | 9
Kate McAlpine
predicted by the standard model. Two separate groups now suggest an explanation for this larger asymmetry lies in the unparticle, a hypothetical entity conjured up in 2007 by theorist Howard Georgi of Harvard University. Georgi suggested that a property known as scale invariance – seen in fractal-like patterns that remain unchanged even when you zoom in and out to
ELASTIC “unparticles” could explain a mysterious signal glimpsed at a particle collider a year ago. That would link a tenuous but intriguing idea to one of the biggest mysteries in physics: why matter prevails over antimatter in the universe. “I think this will increase the unparticle’s credibility as a theory,” says Run-Hui Li of Yonsei University in Seoul, South Korea, “Their charge and spin would be fixed but their the leader of one of two teams mass would vary depending proposing the link. on the viewing scale” Matter and antimatter are thought to have been created in equal amounts after the big bang, different scales, like the branching of redwood trees and the jagged yet something has caused matter edges of coastlines – could apply to be far more dominant than to individual particles too. The antimatter, at least in our patch charge and spin of unparticles of the universe. would be fixed but, counterA possible explanation is that intuitively, their mass would some physical processes favour somehow vary depending on the matter. For example, according scale at which an observer viewed to the standard model of particle the particle. physics, particles known as Such unparticles could play B mesons constantly switch, a role in a popular proposed or mix, between their matter and antimatter forms. Because it is slightly easier for an anti-B meson to become a normal B meson than vice versa, an imbalance accrues. This “uneven mixing” gets transferred to the particles produced when B mesons decay, but alone is not big enough to explain the observed matterantimatter asymmetry. Previously, several teams have glimpsed examples of asymmetry even larger than the standard model predicts. In May 2010, researchers at the Fermi National Accelerator Laboratory in Batavia, Illinois, reported a 1 per cent preference for the number of B mesons produced in their particle smasher, the Tevatron (arxiv.org/ abs/1005.2757). This is 40 times larger than the imbalance
Do gut problems set the brain up for depression?
EARLY digestive problems may hardwire the brain for depression. While gut problems are often linked with depression, they are generally assumed to arise from hormones released because of alterations in mood. Pankaj Pasricha and colleagues at Stanford University in California believe it might be the other way round. Pasricha’s team gave young rats a mild stomach irritant, then tested them for symptoms of depression at 10 weeks old. The rats showed more signs of depression and higher levels of stress hormones in the brain than healthy rats. Jamming signals from nerves in the gut made no difference to their depression, suggesting that ongoing gut pain wasn’t the trigger. Blocking receptors to stress hormones in the brain did alleviate the effects (PLoS One, DOI: 10.1371/journal. pone.0019498). Next Pasricha wants to explore the role of the vagus nerve, which allows the gut to communicate with the brain. Some people are more susceptible to depression than others, however. Understanding genes involved in the disorder could help to explain why. Gerome Breen at King’s College London and colleagues found strong evidence of a genetic link in cases of severe depression. They scanned the genomes of individuals from over 800 families with a history of depression. The results highlight abnormal variations in genes on chromosome 3 (American Journal of Psychiatry, DOI: 10.1176/appi.ajp.2011.10091342). A group from Washington University in St Louis, Missouri, came to the same conclusion – the first time such a finding has been replicated. Understanding which pathways may be affected by these variations, could help personalise medicine. At the moment only half of the people given medication for depression –Do B mesons hold the answer?– respond at all. Catherine de Lange n FERMILAB/SCIENCE PHOTO LIBRARY
‘Unparticle’ boosted by Tevatron signal
extension to the standard model, known as supersymmetry. Xiao-Gang He and his colleagues at Shanghai Jiao Tong University in China calculate that unparticles might also affect the lifetimes of B mesons. That is because quantum mechanics dictates that if they exist, “virtual” versions must exist too. Such transient unparticles would pop in and out of existence and could sometimes affect the lifetimes of real B mesons. And if this influence differed between the B meson and its antimatter counterpart, it could enhance the already uneven mixing predicted by the standard model enough to account for the mysterious Tevatron signal (Journal of Physics Letters B, DOI: 10.1016/j.physletb.2011.03.001). The unparticle’s elastic mass means it could conceivably have avoided detection in the Tevatron until now. A separate group led by Li has come to a similar conclusion (arxiv.org/abs/1012.0095). Bruce Hoeneisen, a member of the Fermilab team that saw the B meson imbalance in 2010, says other options, including new types of quarks not currently included in the standard model, could explain the Tevatron signal. He also cautions that the Tevatron finding requires confirmation. n
21 May 2011 | NewScientist | 9