Minimal Supersymmetric Standard Model

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Minimal Supersymmetric Standard Model

The Minimal Supersymmetric Standard Model (MSSM) is the minimal extension to the Standard Model

Standard Model

The Standard Model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions....
that realizes supersymmetry

Supersymmetry

In particle physics, supersymmetry is a symmetry that relates elementary particles of one Spin to another particle that differs by half a unit of spin and are known as superpartners....
, although non-minimal extensions do exist. Supersymmetry pairs boson

Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
s with fermion

Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s, therefore every Standard Model particle has a partner that has yet to be discovered. If these supersymmetric partners exist, it is likely that they will be observed at the Large Hadron Collider

Large Hadron Collider

The Large Hadron Collider is the List of accelerators in particle physics#Hadron colliders particle accelerator, intended to Collider opposing Charged particle beam, of either protons at an energy of 7 TeV/particle, or lead nuclei at an energy of 574 TeV/nucleus....
, which began operations in 2009. If the superparticles are found, it is analogous to discovering antimatter

Antimatter

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....
and depending on the details of what is found, it could provide evidence for grand unification and might even in principle provide hints as to how string theory

String theory

String theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum gravity. The String s of string theory are one-dimensional oscillating lines, but they are no longer considered fundamental to the theory, which can be formulated in terms of points or surfaces too....
describes nature.

The MSSM was originally proposed in 1981 to stabilize the weak scale, solving the hierarchy problem

Hierarchy problem

In theoretical physics, a hierarchy problem occurs when the fundamental parameters of some Lagrangian mechanics are vastly different from the parameters measured by experiment....
.

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The Minimal Supersymmetric Standard Model (MSSM) is the minimal extension to the Standard Model

Standard Model

Supersymmetry

Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
s with fermion

Fermion

Large Hadron Collider

Antimatter

String theory

Hierarchy problem

In theoretical physics, a hierarchy problem occurs when the fundamental parameters of some Lagrangian mechanics are vastly different from the parameters measured by experiment....
. The Higgs

Higgs

The term Higgs appears in:* Alan Higgs, English businessman and philanthropist* Eric Sidney Higgs, English archaeologist* Sir Derek Higgs, an English business leader and merchant banker...
mass of the Standard Model is unstable to quantum corrections and the theory predicts that weak scale should be much weaker than what is observed to be. In the MSSM, the Higgs boson

Higgs boson

In particle physics, the Higgs boson is a massive Scalar field theory elementary particle predicted to exist by the Standard Model.The Higgs boson is the only Standard Model particle that has not yet been observed....
has a fermionic superpartner, the Higgsino

Higgsino

In particle physics, a Higgsino is the hypothetical superpartner of the Higgs boson, as predicted by supersymmetry. The Higgsino is a Dirac fermion and that is a weak isodoublet with hypercharge half under the Standard Model gauge symmetries....
, that has the same mass as it would if supersymmetry were an exact symmetry. Because fermion masses are radiatively stable, the Higgs mass inherits this stability.

The only unambiguous way to claim discovery of supersymmetry is to produce superparticles in the laboratory. Because superparticles are expected to be 100 to 1000 times heavier than the proton, it requires a huge amount of energy to make these particles that can only be achieved at particle accelerators. Currently the Tevatron

Tevatron

Tevatron is a circular particle accelerator at the Fermilab in Batavia, Illinois and is the highest energy particle collider in the world until collisions begin at the Large Hadron Collider....
is the highest energy particle collider and is actively looking for evidence of the production of supersymmetric particles. Most physicists believe that supersymmetry must be discovered at the LHC

Large Hadron Collider

The Large Hadron Collider is the List of accelerators in particle physics#Hadron colliders particle accelerator, intended to Collider opposing Charged particle beam, of either protons at an energy of 7 TeV/particle, or lead nuclei at an energy of 574 TeV/nucleus....
if it is responsible for stabilizing the weak scale. There are five classes of particle that superpartners of the Standard Model fall into: squarks, gluino

Gluino

A gluino is the hypothetical supersymmetric partner of the gluon. Gluinos are Majorana fermions and interact via the strong interaction as an octet of color....
s, chargino

Chargino

Neutralino

In particle physics, the neutralino is a hypothetical particle, part of the doubling of the menagerie of particles predicted by supersymmetry theories....
s, and sleptons. These superparticles have their interactions and subsequent decays described by the MSSM and each has characteristic signatures.

The MSSM imposes R-parity

R-parity

Proton decay

In particle physics, proton decay is a Hypothesis form of radioactive decay in which the proton decays into lighter subatomic particles, usually a neutral pion and a positron....
. It adds supersymmetry breaking by introducing explicit soft supersymmetry breaking operators into the Lagrangian that is communicated to it by some unknown (and unspecified) dynamics. This means that there are 120 new parameters in the MSSM. Most of these parameters lead to unnacceptable phenomenology such as large flavor changing neutral current

Flavor changing neutral current

In theoretical physics, flavor changing neutral currents are expressions that change the flavor of a fermion current without altering its electric charge....
s or large electric dipole moment

Electric dipole moment

In physics, the electric dipole moment is a measure of the Polarity of a system of electric charges called dipole.In the simple case of two point charges, one with charge and one with charge , the electric dipole moment is:...
s for the neutron and electron. To avoid these problems, the MSSM takes all of the soft susy breaking to be diagonal in flavor space and for all of the new CP violating phases to vanish.

Theoretical Motivations

There are three principle motivations for the MSSM over other theoretical extensions of the Standard Model, namely:

Naturalness
Gauge coupling unification
Dark Matter

These motivations come out without much effort and they are the primary reasons why the MSSM is the leading candidate for a new theory to be discovered at collider experiments such as the Tevatron

Tevatron

Large Hadron Collider

Naturalness

The original motivation for proposing the MSSM was to stabilize the Higgs mass to radiative corrections that are quadratically divergent in the Standard Model (hierarchy problem

Hierarchy problem

In theoretical physics, a hierarchy problem occurs when the fundamental parameters of some Lagrangian mechanics are vastly different from the parameters measured by experiment....
). In supersymmetric models, scalars are related to fermions and have the same mass. Since fermion masses are logarithmically divergent, scalar masses inherit the same radiative stability. The Higgs vacuum expectation value is related to the negative scalar mass in the Lagrangian. In order for the radiative corrections to the Higgs mass to not be dramatically larger than the actual value, the mass of the superpartners of the Standard Model should not be significantly heavier than the Higgs vev

Vacuum expectation value

In quantum field theory the vacuum expectation value of an Operator is its average, expected value in the Vacuum#The quantum-mechanical vacuum....
-- roughly 100 GeV. This mass scale is being probed currently at the Tevatron

Tevatron

Large Hadron Collider

Gauge Coupling Unification

If the superpartners of the Standard Model are near the TeV scale, then measured gauge couplings of the three gauge groups unify at high energies. The beta-function

Beta-function

In theoretical physics, specifically quantum field theory, a beta-function ? encodes the dependence of a Coupling constant, g, on the energy scale, of a given physical process....
s for the MSSM gauge couplings are given by

Gauge Group
SU(3)	8.5
SU(2)	29.6
U(1)	59.2

where is measured in SU(5) normalization -- a factor of different than the Standard Model's nomalization and predicted by Georgi-Glashow SU(5) .

The condition for gauge coupling unification at one loop is whether the following expression is satisfied .

Remarkably, this is precisely satisfied to experimental errors in the values of . There are two loop corrections and both TeV-scale and GUT-scale threshold corrections that alter this condition on gauge coupling unification, and the results of more extensive calculations reveal that gauge coupling unification occurs to an accuracy of 1%, though this is about 3 standard deviations from the theoretical expectations.

This prediction is generally considered as indirect evidence for both the MSSM and SUSY GUT

Grand unification theory

Grand Unification, grand unified theory, or GUT refers to any of several very similar unified field theory or models in physics that predicts that at extremely high energies , the electromagnetic, weak nuclear, and strong nuclear forces are fused into a single unified field....
s. It should be noted that gauge coupling unification does not necessarily imply grand unification and there exist other mechanisms to reproduce gauge coupling unification. However, if superpartners are found in the near future, the apparent success of gauge coupling unification would suggest that a supersymmetric grand unified theory is a promising candidate for high scale physics.

Dark Matter

If R-parity

R-parity

Lightest Supersymmetric Particle

In particle physics, the Lightest Supersymmetric Particle is the generic name given to the lightest of the additional hypothetical particles found in Minimal_Supersymmetric_Standard_Model....
) of the MSSM is stable and is a weakly interacting massive particle (WIMP

WIMP

In astrophysics, weakly interacting massive particles, or WIMPs, are hypothetical particles serving as one possible solution to the dark matter problem....
) — i.e. it does not have electromagnetic or strong interactions. This makes the LSP a good dark matter

Dark matter

In astronomy and physical cosmology, dark matter is Hypothesis matter that is undetectable by its emitted electromagnetic radiation, but whose presence can be inferred from gravity effects on visible matter....
candidate and falls into the category of cold dark matter

Cold dark matter

Cold dark matter is a refinement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material that cannot be observed by its electromagnetic radiation and hence is dark while at the same time the particles making up this matter are slow and hence are cold....
(CDM) particle.

Predictions of the MSSM Regarding Hadron Colliders

The Tevatron

Tevatron

Large Hadron Collider

The Large Hadron Collider is the List of accelerators in particle physics#Hadron colliders particle accelerator, intended to Collider opposing Charged particle beam, of either protons at an energy of 7 TeV/particle, or lead nuclei at an energy of 574 TeV/nucleus....
have active experimental programs searching for supersymmetric particles. Since both of these machines are hadron

Hadron

In particle physics, a hadron is a bound state of quarks. Hadrons are held together by the strong interaction, similarly to how molecules are held together by the electromagnetic force....
colliders — proton antiproton for the Tevatron and proton proton for the LHC — they search best for strongly interacting particles. Therefore most experimental signature involve production of squarks or gluino

Gluino

A gluino is the hypothetical supersymmetric partner of the gluon. Gluinos are Majorana fermions and interact via the strong interaction as an octet of color....
s. Since the MSSM has R-parity

R-parity

R-parity is a concept in particle physics. In the MSSM of the standard model, baryon number and lepton number are no longer conserved by all of the renormalizable couplings...
, the lightest supersymmetric particle is stable and after the squarks and gluinos decay each decay chain will contain one LSP that will leave the detector unseen. This leads to the generic prediction that the MSSM will produce a 'missing energy

Missing energy

In experimental physics particle physics, missing energy refers to energy which is not detected in a particle detector, but is expected because of conservation of energy and conservation of momentum....
' signal from these particles leaving the detector.

Neutralinos

There are four Neutralino

Neutralino

In particle physics, the neutralino is a hypothetical particle, part of the doubling of the menagerie of particles predicted by supersymmetry theories....
s that are fermions and are electrically neutral, the lightest of which is typically stable. They are typically labeled . These four states are mixtures of the Bino, neutral Wino, and neutral Higgsinos. Because these particles only interact with the weak vector bosons, they are not directly produced at hadron colliders in copious numbers. They primarily appear as particles in cascade decays of heavier particles usually originating from colored supersymmetric particles such as squarks or gluinos.

In R-parity

R-parity

R-parity is a concept in particle physics. In the MSSM of the standard model, baryon number and lepton number are no longer conserved by all of the renormalizable couplings...
conserving models, the lightest neutralino is stable and all supersymmetric cascades decays end up decaying into this particle which leaves the detector unseen and its existence can only be inferred by looking for unbalanced momentum in a detector.

The heavier neutralinos typically decay through a to a lighter neutralino or through a to chargino. Thus a typical decay is

Missing energy +
Missing energy +

The mass splittings between the different Neutralinos will dictate which patterns of decays are allowed.

Charginos

There are two Chargino

Chargino

The chargino is a hypothetical supersymmetric particle. It refers to the mass eigenstates of a charged superpartner, i.e. any new electrically charged fermion predicted by supersymmetry....
s that are fermions and are electrically charged. The heavier chargino can decay through to the lighter chargino. Both can decay through a to neutralino.

Squarks

The squarks are the scalar superpartners of the quarks and there is one version for each Standard Model quark. Due to phenomenological constraints from flavor changing neutral currents, typically the lighter two generations of squarks have to be nearly the same in mass and therefore are not given distinct names. The superpartners of the top and bottom quark can be split from the lighter squarks and are called stop and sbottom.

Squarks can be produced through strong interactions and therefore are easily produced at hadron colliders. They decay to quarks and neutralinos or charginos which further decay. Squarks are typically pair produced and therefore a typical signal is

2 jets + Missing energy
2 jets + 2 leptons + Missing energy

Gluinos

Gluinos are Majorana

Majorana

Majorana may refer to:* Majorana equation, a relativistic wave equation* Majorana fermion, a concept in particle physics* Majorana spinor, a concept in quantum field theory...
fermionic partners of the gluon

Gluon

Gluons are elementary particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei....
which means that they are their own antiparticles. They interact strongly and therefore can be produced significantly at the LHC. They can only decay to a quark and a squark and thus a typical gluino signal is

4 jets + Missing energy

Because gluinos are Majorana, gluinos can decay to either a quark+anti-squark or an anti-quark+squark with equal probability. Therefore pairs of gluinos can decay to

4 jets+ + Missing energy

This is a distinctive signature because it has same-sign di-leptons and has very little background in the Standard Model.

Sleptons

Sleptons are the scalar partners of the lepton

Lepton

Leptons are a family of elementary particles, alongside quarks and gauge bosons . Like quarks, leptons are fermions and are subject to the electromagnetic force, the gravitational force, and weak interaction....
s of the Standard Model. They are not strongly interacting and therefore are not produced very often at hadron colliders unless they are very light. They will typically be found in decays of a charginos and neutralinos if they are light enough to be a decay product

MSSM Fields

Fermion

Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
ic superpartners, and bosons have fermionic superpartners. For most of the Standard Model particles, doubling is very straightforward. However, for the Higgs boson, it is more complicated.

A single Higgsino (the fermionic superpartner of the Higgs boson) would lead to a gauge anomaly

Gauge anomaly

In theoretical physics, a gauge anomaly is an example of an anomaly : it is an effect of quantum mechanics?usually a one-loop diagram?that invalidates the gauge symmetry of a quantum field theory; i.e....
and would cause the theory to be inconsistent. However if two Higgsinos are added, there is no gauge anomaly. The simplest theory is one with a two Higgsinos and therefore two scalar Higgs doublets. Another reason for having two scalar Higgs doublets rather than one is in order to have Yukawa couplings

Yukawa interaction

In particle physics, Yukawa's interaction, named after Hideki Yukawa, is an interaction between a scalar field and a Dirac field of the type...
between the Higgs and both down-type quark

Quark

Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....
s and up-type quark

Quark

Complex conjugate

In mathematics, the complex conjugate of a complex number is given by changing the sign of the imaginary part. Thus, the conjugate of the complex number...
(which has Y=+1/2). However in a supersymmetric theory this is not allowed, so two types of Higgs fields are needed.

MSSM Superfields

In supersymmetric theories, every field and its superpartner can be written together as a superfield

Superfield

In theoretical physics, one often analyzes theories with supersymmetry in which superfields play a very important role. In four dimensions, the simplest example - namely the minimal N=1 supersymmetry - may be written using a superspace....
. The superfield formulation of supersymmetry is very convenient to write down manifestly supersymmetric theories (i.e. one does not have to tediously check that the theory is supersymmetric term by term in the Lagrangian). The MSSM contains vector superfield

Vector superfield

SUSY in 4D In theoretical physics, one often analyzes theories with supersymmetry which also haveinternal gauge symmetries. So, it is important to come up with a supersymmetric generalization...
s associated with the Standard Model gauge groups which contain the vector bosons and associated gauginos. It also contains chiral superfield

Chiral superfield

In theoretical physics, one often analyzes theories with supersymmetry in which chiral superfields play an important role. In four dimensions, the minimal N=1 supersymmetry may be written using the notion of superspace....
s for the Standard Model fermions and Higgs bosons (and their respective superpartners).

field	multiplicity	Z₂-parity	Standard Model particle
Q	3	–	left-handed Chirality (physics) A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle.... quark
U^c	3	–	left-handed Chirality (physics) A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle.... up-type anti-quark Quark Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....
D^c	3	–	left-handed Chirality (physics) A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle.... down-type anti-quark Quark Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....
L	3	–	left-handed Chirality (physics) A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle.... lepton
E^c	3	–	left-handed Chirality (physics) A phenomenon is said to be chiral if it is not identical to its mirror image . The Spin of a particle may be used to define a handedness for that particle.... charged anti-lepton
H_u	1	+	Higgs
H_d	1	+	Higgs

The MSSM Lagrangian

The Lagrangian for the MSSM contains several pieces.

The first is the Kahler potential for the matter and Higgs fields which produces the kinetic terms for the fields.

The second piece is the gauge field superpotential that produces the kinetic terms for the gauge bosons and gauginos.

The next term is the superpotential
Superpotential

Superpotential is a concept from particle physics' supersymmetry....
for the matter and Higgs fields. These produce the Yukawa couplings for the Standard Model fermions and also the mass term for the Higgsinos. After imposing R-parity
R-parity

R-parity is a concept in particle physics. In the MSSM of the standard model, baryon number and lepton number are no longer conserved by all of the renormalizable couplings...
, the renormalizable, gauge invariant operators in the superpotential are

The constant term is unphysical in global supersymmetry (as opposed to supergravity

Supergravity

Soft Susy Breaking

The last piece of the MSSM Lagrangian is the soft supersymmetry breaking Lagrangian. The vast majority of the parameters of the MSSM are in the susy breaking Lagrangian. The soft susy breaking are divided into roughly three pieces.

The first are the gaugino masses

Where are the gauginos and is different for the wino, bino and gluino.

The next are the soft masses for the scalar fields

where are any of the scalars in the MSSM and are hermitean matrices for the squarks and sleptons of a given gauge quantum numbers. The eigenvalues of these matrices are actually the masses squared, rather than the masses.

Finally there are the and terms which are given by

The terms are complex matrices much as the scalar masses are.

Problems with the MSSM

There are several problems with the MSSM — most of them falling into understanding the parameters.

The mu problem
Mu problem

In theoretical physics, the μ problem is a problem of supersymmetry theories, concerned with understanding the parameters of the theory.The supersymmetric Higgs mass parameter μ appears as the following term in the superpotential: μHuHd....
: The supersymmetric Higgs
Higgs

The term Higgs appears in:* Alan Higgs, English businessman and philanthropist* Eric Sidney Higgs, English archaeologist* Sir Derek Higgs, an English business leader and merchant banker...
mass parameter µ appears as the following term in the superpotential
Superpotential

Superpotential is a concept from particle physics' supersymmetry....
: µH_uH_d. It should have the same order of magnitude as the electroweak scale
Electroweak scale

In particle physics, the electroweak scale is the energy scale around 246 GeV, a typical energy of processes described by the electroweak theory. The particular number 246 GeV is taken to be the vacuum expectation value of the Higgs field ....
, many orders of magnitude smaller than that of the planck scale
Planck scale

In particle physics and physical cosmology, the Planck scale is an energy scale around 1.22 ? 1028 eV at which quantum mechanics of gravity become strong....
, which is the natural cutoff
Cutoff

In theoretical physics, cutoff is the maximal or minimal value of energy, momentum, or length, so that the objects with even larger or smaller values than these physical quantity are ignored....
scale. The soft supersymmetry breaking terms should also be of the same order of magnitude as the electroweak scale
Electroweak scale

In particle physics, the electroweak scale is the energy scale around 246 GeV, a typical energy of processes described by the electroweak theory. The particular number 246 GeV is taken to be the vacuum expectation value of the Higgs field ....
. This brings about a problem of naturalness
Naturalness (particle physics)

In particle physics, the assumption of naturalness means that unless a more detailed explanation exists, all conceivable terms in the effective action that preserve the required symmetries should appear in this effective action with natural coefficients....
: why are these scales so much smaller than the cutoff scale yet happen to fall so close to each other?
Flavor universality of soft masses and A-terms: since no flavor mixing additional to that predicted by the standard model
Standard Model

The Standard Model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions....
has been discovered so far, the coefficients of the additional terms in the MSSM Lagrangian must be, at least approximately, flavor
Flavor

Flavor or flavour is the sensory impression of a food or other chemical substance, and is determined mainly by the chemical senses of taste and olfaction....
invariant (i.e. the same for all flavors).
Smallness of CP violating phases: since no CP violation
CP violation

In particle physics, CP violation is a violation of the postulated CP symmetry, the combination of C symmetry and P symmetry. CP symmetry states that the laws of physics should be the same if a particle is interchanged with its antiparticle , and left and right were swapped ....
additional to that predicted by the standard model
Standard Model

The Standard Model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions....
has been discovered so far, the additional terms in the MSSM Lagrangian must be, at least approximately, CP invariant, so that their CP violating phases are small.

More recently physicists have become concerned about the non-discovery of the Higgs boson

Higgs boson

Tevatron

Tevatron is a circular particle accelerator at the Fermilab in Batavia, Illinois and is the highest energy particle collider in the world until collisions begin at the Large Hadron Collider....
; many nevertheless hold out hope on account of the possibility that the Large Hadron Collider

Large Hadron Collider

CERN

The European Organization for Nuclear Research , known as CERN , , is the world's largest particle physics laboratory, situated in the northwest suburbs of Geneva on the France-Switzerland border, established in 1954 in science....
in 2009 will discover it.

Theories of Supersymmetry breaking

A large amount of theoretical effort has been spent trying to understand the mechanism for soft supersymmetry breaking

Supersymmetry breaking

In particle physics, supersymmetry breaking is the process to obtain a seemingly non-supersymmetric physics from a supersymmetric theory which is a necessary step to reconcile supersymmetry with actual experiments....
that produces the desired properties in the superpartner masses and interactions. The three most extensively studied mechanisms are

Gravity Mediated Supersymmetry Breaking

Gravity Mediated Supersymmetry Breaking is a method of communicating supersymmetry breaking to the supersymmetric Standard Model through gravitational interactions. It was the first method proposed to communicate supersymmetry breaking. In gravity mediated supersymmetry breaking models, there is a part of the theory that only interacts with the MSSM through gravitational interaction. This hidden sector of the theory breaks supersymmetry. Through the supersymmetric version of the Higgs mechanism

Higgs mechanism

In quantum field theory, the Higgs mechanism is a way that the massless gauge bosons in a gauge theory get a mass by interacting with a background Higgs field....
, the gravitino

Gravitino

The gravitino is the supersymmetry partner of the graviton, as predicted by theories combining general relativity and supersymmetry; i.e. supergravity theories....
, the supersymmetric version of the graviton, acquires a mass. After the gravitino has a mass, gravitational radiative corrections to soft masses are incompletely cancelled beneath the gravitino's mass.

It is currently believed that it is not generic to have a sector completely decoupled from the MSSM and there should be higher dimension operators that couple different sectors together with the higher dimension operators suppressed by the Planck scale. These operators give as large of a contribution to the soft supersymmetry breaking masses as the gravitational loops; therefore, today people usually consider gravity mediation to be gravitational sized direct interactions between the hidden sector and the MSSM.

mSUGRA stands for minimal supergravity. The construction of a realistic model of interactions within N = 1 supergravity

Supergravity

In theoretical physics, supergravity is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry ....
framework where supersymmetry breaking is communicated through the supergravity interactions was carried out by Ali Chamseddine, Richard Arnowitt

Richard Arnowitt

Richard L. Arnowitt is an United States physicist known for his contributions to theoretical particle physics and to general relativity.Arnowitt is a Distinguished Professor at Texas A&M University, where he is a member of the Department of Physics....
and Pran Nath

Pran Nath

Pran Nath is a theoretical physicist working at Northeastern University, with research focus in elementary particle physics. He holds a Matthews Distinguished University Professor chair....
in 1982 . mSUGRA is one of the most widely investigated models of particle physics

Particle physics

Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
due to its predictive power requiring only 4 input parameters and a sign, to determine the low energy phenomenology from the scale of Grand Unification.

Gravity Mediated Supersymmetry Breaking was assumed to be flavor universal because of the universality of gravity; however, in 1986 Hall, Kostelecky, and Raby showed that Planck scale physics that are necessary to generate the Standard Model Yukawa couplings spoil the universality of the supersymmetry breaking.

Gauge Mediated Supersymmetry Breaking (GMSB)

Gauge Mediated Supersymmetry Breaking is method of communicating supersymmetry breaking to the supersymmetric Standard Model through the Standard Model's gauge interactions. Typically a hidden sector breaks supersymmetry and communicates it to massive messenger fields that are charged under the Standard Model. These messenger fields induce a gaugino mass at one loop and then this is transmitted on to the scalar superpartners at two loops.

Anomaly Mediated Supersymmetry Breaking (AMSB)

Anomaly Mediate Supersymmetry Breaking is special type of gravity mediated supersymmetry breaking that results in supersymmetry breaking being communicated to the supersymmetric Standard Model through the conformal anomaly.

External links

by Stephen P. Martin