Mirror matter
Encyclopedia
In physics
, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.
Modern physics deals with three basic types of spatial symmetry
: reflection, rotation and translation. The known elementary particles respect rotation and translation symmetry but do not respect mirror reflection symmetry (also called P-symmetry or parity). Of the four fundamental interactions—electromagnetism
, the strong interaction
, the weak interaction
, and gravity
—only the weak interaction breaks parity.
Parity violation in weak interactions was first postulated by Tsung Dao Lee and Chen Ning Yang in 1956 as a solution to the τ-θ puzzle. They suggested a number of experiments to test if the weak interaction is invariant under parity. These experiments were performed half a year later and they confirmed that the weak interactions of the known particles violate parity.
However parity symmetry can be restored as a fundamental symmetry of nature if the particle content is enlarged
so that every particle has a mirror partner. The theory in its modern form was written down in 1991, although the basic idea dates back earlier. Mirror particles interact amongst themselves in the same way as ordinary particles, except where ordinary particles have left-handed interactions, mirror particles have right-handed interactions. In this way, it turns out that mirror reflection symmetry can exist as an exact symmetry of nature, provided that a "mirror" particle exists for every ordinary particle. Parity can also be spontaneously broken depending on the Higgs potential. While in the case of unbroken parity symmetry the masses of particles are the same as their mirror partners, in case of broken parity symmetry the mirror partners are lighter or heavier.
Mirror matter, if it exists, would have to be very weakly interacting with ordinary matter. This is because the forces between mirror particles are mediated by mirror boson
s. With the exception of the graviton
, none of the known bosons can be identical to their mirror partners. The only way mirror matter can interact with ordinary matter via forces other than gravity is via so-called kinetic mixing of mirror bosons with ordinary bosons or via the exchange of Holdom particles. These interactions can only be very weak. Mirror particles have therefore been suggested as candidates for the inferred dark matter
in the universe.
In another context, mirror matter has been proposed to give rise to an effective Higgs mechanism
responsible for the electroweak symmetry breaking. In such a scenario, mirror fermion
s have masses on the order of 1 TeV since they interact with an additional interaction, while some of the mirror boson
s are identical to the ordinary gauge bosons. In order to emphasize the distinction of this model from the ones above, these mirror particles are usually called katoptrons.
What if mirror matter does exist but has (almost) zero abundance? Like magnetic monopole
s, mirror matter could have been diluted to unobservably low densities during the inflation
epoch. Sheldon Glashow
has shown that if at some high energy scale particles exist which interact strongly with both ordinary and mirror particles, radiative corrections
will lead to a mixing between photon
s and mirror photon
s. This mixing has the effect of giving mirror electric charges a very small ordinary electric charge. Another effect of photon-mirror photon mixing is that it induces oscillations between positronium
and mirror positronium. Positronium could then turn into mirror positronium and then decay into mirror photons.
The mixing between photons and mirror photons could be present in tree level Feynman diagram
s or arise as a consequence of quantum corrections due to the presence of particles that carry both ordinary and mirror charges. In the latter case, the quantum corrections have to vanish at the one and two loop level Feynman diagrams, otherwise the predicted value of the kinetic mixing parameter would be larger than experimentally allowed.
An experiment to measure this effect is currently being planned.
If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA/NaI
and its successor DAMA/LIBRA
. In fact, it is one of the few dark matter candidates which can explain
the positive DAMA/NaI dark matter signal whilst still being consistent
with the null results of other dark matter experiments.
Mirror matter may also be detected in electromagnetic field penetration experiments and there would also be consequences for planetary science.
Mirror matter could also be responsible for the GZK puzzle
. Topological defect
s in the mirror sector could produce mirror neutrinos which can oscillate to ordinary neutrinos. Another possible way to evade the GZK bound is via neutron-mirror neutron oscillations.
, in an attempt to emphasize that antimatter is identical to ordinary matter, except reversed in all possible ways (i.e., CPT). (Forward was apparently not aware of the use of the word "mirror particles" by Russian physicists to mean parity reversed matter that does not interact strongly with "ordinary" matter). This is elucidated in his book Mirror Matter: Pioneering Antimatter Physics (1988), and his editing the small review journal Mirror Matter Newsletter (1986–1990). However, this use of the term "mirror matter" for antimatter was never widely picked up by others and is not currently in common use.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, mirror matter, also called shadow matter or Alice matter, is a hypothetical counterpart to ordinary matter.
Modern physics deals with three basic types of spatial symmetry
Symmetry
Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...
: reflection, rotation and translation. The known elementary particles respect rotation and translation symmetry but do not respect mirror reflection symmetry (also called P-symmetry or parity). Of the four fundamental interactions—electromagnetism
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
, the strong interaction
Strong interaction
In particle physics, the strong interaction is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. As with the other fundamental interactions, it is a non-contact force...
, the weak interaction
Weak interaction
Weak interaction , is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars...
, and gravity
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
—only the weak interaction breaks parity.
Parity violation in weak interactions was first postulated by Tsung Dao Lee and Chen Ning Yang in 1956 as a solution to the τ-θ puzzle. They suggested a number of experiments to test if the weak interaction is invariant under parity. These experiments were performed half a year later and they confirmed that the weak interactions of the known particles violate parity.
However parity symmetry can be restored as a fundamental symmetry of nature if the particle content is enlarged
so that every particle has a mirror partner. The theory in its modern form was written down in 1991, although the basic idea dates back earlier. Mirror particles interact amongst themselves in the same way as ordinary particles, except where ordinary particles have left-handed interactions, mirror particles have right-handed interactions. In this way, it turns out that mirror reflection symmetry can exist as an exact symmetry of nature, provided that a "mirror" particle exists for every ordinary particle. Parity can also be spontaneously broken depending on the Higgs potential. While in the case of unbroken parity symmetry the masses of particles are the same as their mirror partners, in case of broken parity symmetry the mirror partners are lighter or heavier.
Mirror matter, if it exists, would have to be very weakly interacting with ordinary matter. This is because the forces between mirror particles are mediated by mirror boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....
s. With the exception of the graviton
Graviton
In physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton must be massless and must have a spin of 2...
, none of the known bosons can be identical to their mirror partners. The only way mirror matter can interact with ordinary matter via forces other than gravity is via so-called kinetic mixing of mirror bosons with ordinary bosons or via the exchange of Holdom particles. These interactions can only be very weak. Mirror particles have therefore been suggested as candidates for the inferred dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
in the universe.
In another context, mirror matter has been proposed to give rise to an effective Higgs mechanism
Higgs mechanism
In particle physics, the Higgs mechanism is the process in which gauge bosons in a gauge theory can acquire non-vanishing masses through absorption of Nambu-Goldstone bosons arising in spontaneous symmetry breaking....
responsible for the electroweak symmetry breaking. In such a scenario, mirror fermion
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....
s have masses on the order of 1 TeV since they interact with an additional interaction, while some of the mirror boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....
s are identical to the ordinary gauge bosons. In order to emphasize the distinction of this model from the ones above, these mirror particles are usually called katoptrons.
Observational effects of mirror matter
If mirror matter is present in the universe with sufficient abundance then its gravitational effects can be detected. Because mirror matter is analogous to ordinary matter, it is then to be expected that a fraction of the mirror matter exists in the form of mirror galaxies, mirror stars, mirror planets etc. These objects can be detected using gravitational microlensing. One would also expect that some fraction of stars have mirror objects as their companion. In such cases one should be able to detect periodic Doppler shifts in the spectrum of the star. There are some hints that such effects may already have been observed.What if mirror matter does exist but has (almost) zero abundance? Like magnetic monopole
Magnetic monopole
A magnetic monopole is a hypothetical particle in particle physics that is a magnet with only one magnetic pole . In more technical terms, a magnetic monopole would have a net "magnetic charge". Modern interest in the concept stems from particle theories, notably the grand unified and superstring...
s, mirror matter could have been diluted to unobservably low densities during the inflation
Cosmic inflation
In physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized extremely rapid exponential expansion of the early universe by a factor of at least 1078 in volume, driven by a negative-pressure vacuum energy density. The inflationary epoch comprises the first part...
epoch. Sheldon Glashow
Sheldon Lee Glashow
Sheldon Lee Glashow is a Nobel Prize winning American theoretical physicist. He is the Metcalf Professor of Mathematics and Physics at Boston University.-Birth and education:...
has shown that if at some high energy scale particles exist which interact strongly with both ordinary and mirror particles, radiative corrections
Effective field theory
In physics, an effective field theory is, as any effective theory, an approximate theory, that includes appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale, while ignoring substructure and degrees of freedom at shorter distances .-The renormalization...
will lead to a mixing between photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s and mirror photon
Mirror photon
The mirror photon is the mirror counterpart of the photon. It may be massless or massive in theory. Mirror photons and other mirror matter particles have been proposed as a candidate for dark matter. The mirror photon is also invisible and undetectable, except for their gravitational effects...
s. This mixing has the effect of giving mirror electric charges a very small ordinary electric charge. Another effect of photon-mirror photon mixing is that it induces oscillations between positronium
Positronium
Positronium is a system consisting of an electron and its anti-particle, a positron, bound together into an "exotic atom". Being unstable, the two particles annihilate each other to produce two gamma ray photons after an average lifetime of 125 ps or three gamma ray photons after 142 ns in...
and mirror positronium. Positronium could then turn into mirror positronium and then decay into mirror photons.
The mixing between photons and mirror photons could be present in tree level Feynman diagram
Feynman diagram
Feynman diagrams are a pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, first developed by the Nobel Prize-winning American physicist Richard Feynman, and first introduced in 1948...
s or arise as a consequence of quantum corrections due to the presence of particles that carry both ordinary and mirror charges. In the latter case, the quantum corrections have to vanish at the one and two loop level Feynman diagrams, otherwise the predicted value of the kinetic mixing parameter would be larger than experimentally allowed.
An experiment to measure this effect is currently being planned.
If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA/NaI
DAMA/NaI
The DAMA/NaI experiment was designed to detect dark matter using the direct detection technique. It was located at the Laboratori Nazionali del Gran Sasso in Italy and collected data during the period 1996-2002...
and its successor DAMA/LIBRA
DAMA/LIBRA
The DAMA/LIBRA experiment is an experiment designed to detect dark matter using the direct detection technique. It is located at the Laboratori Nazionali del Gran Sasso in Italy. The successor to the DAMA/NaI experiment, it uses very similar detector technology but has a larger target mass of...
. In fact, it is one of the few dark matter candidates which can explain
the positive DAMA/NaI dark matter signal whilst still being consistent
with the null results of other dark matter experiments.
Mirror matter may also be detected in electromagnetic field penetration experiments and there would also be consequences for planetary science.
Mirror matter could also be responsible for the GZK puzzle
Greisen-Zatsepin-Kuzmin limit
The Greisen–Zatsepin–Kuzmin limit is a theoretical upper limit on the energy of cosmic rays coming from "distant" sources. The limit is 5×1019 eV, or about 8 joules. The limit is set by slowing-interactions of cosmic ray protons with the microwave background radiation over long distances...
. Topological defect
Topological defect
In mathematics and physics, a topological soliton or a topological defect is a solution of a system of partial differential equations or of a quantum field theory homotopically distinct from the vacuum solution; it can be proven to exist because the boundary conditions entail the existence of...
s in the mirror sector could produce mirror neutrinos which can oscillate to ordinary neutrinos. Another possible way to evade the GZK bound is via neutron-mirror neutron oscillations.
Alternate terminology
The phrase "mirror matter" was also introduced by physicist and author Dr. Robert L. Forward as an alternative term for what is commonly called antimatterAntimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
, in an attempt to emphasize that antimatter is identical to ordinary matter, except reversed in all possible ways (i.e., CPT). (Forward was apparently not aware of the use of the word "mirror particles" by Russian physicists to mean parity reversed matter that does not interact strongly with "ordinary" matter). This is elucidated in his book Mirror Matter: Pioneering Antimatter Physics (1988), and his editing the small review journal Mirror Matter Newsletter (1986–1990). However, this use of the term "mirror matter" for antimatter was never widely picked up by others and is not currently in common use.
External links
- A collection of scientific articles on various aspects of mirror matter theory
- Mirror matter article on h2g2H2g2h2g2 is a British-based collaborative online encyclopedia project engaged in the construction of, in its own words, "an unconventional guide to life, the universe, and everything", in the spirit of the fictional publication The Hitchhiker's Guide to the Galaxy from the science fiction comedy series...