Proton Decay Rate Research Articles

Detailed Analysis of Proton Decay Rate in the Minimal Supersymmetric SO(10) Model

We consider the minimal supersymmetric SO(10) model, where only one 10 and one Higgs multiplets have Yukawa couplings with matter multiplets. This model has the high predictive power for the Yukawa coupling matrices consistent with the experimental data of the charged fermion mass matrices, and all the Yukawa coupling matrices are completely determined once a few parameters in the model are fixed. This feature is essential for definite predictions to the proton decay rate through the dimension five operators. Althogh it is not completely general, we analyze the proton decay rate for the dominant decay modes p→K + by including as many free parameters as possible and varying them. There are two free parameters in the Yukawa sector, while three in the Higgsino sector. It is found that an allowed region exists when the free parameters in the Higgs sector are tuned so as to cancel the proton decay amplitude. The resultant proton lifetime is proportional to 1/tan 2β and the allowed region eventually disappears as tan β becomes large.

PROTON DECAY IN SUPERSYMMETRIC GUT MODELS

The instability of protons is a crucial prediction of supersymmetric GUTs. We review the decay in minimal supersymmetric SU (5), which is dominated by dimension-five operators, and discuss the implications of the failure of Yukawa unification for the decay rate. In a consistent SU (5) model, where SU (5) relations among Yukawa couplings hold, the proton decay rate can be several orders of magnitude smaller than the present experimental bound. Finally, we discuss orbifold GUTs, where proton decay via dimension-five operators is absent. The branching ratios of dimension-six decay can significantly differ from those in four dimensions.

Erratum: Proton decay due to bulk SU(5) gauge bosons in the Randall-Sundrum scenario [Phys. Rev. D66, 024011 (2002)

We calculate the proton decay rate due to five dimensional SU(5) gauge bosons in the Randall-Sundrum scenario with two branes (Planck brane and TeV brane). We consider matter in the usual 10 and \bar 5 SU(5) representations localized on a brane, and consider the case when SU(5) is broken by a Higgs mechanism on the matter brane. We calculate the proton decay rate mediated by X bosons, due to terms in the Lagrangian with X and its derivative along the extra dimension. We confirm that the experimental limit on the proton decay rate allows SU(5) matter to be on the Planck brane, but excludes it from being on the TeV brane in this scenario.

Proton decay of the highly deformed odd-odd nucleusEu130

The proton decay of the highly deformed odd-odd nucleus $^{130}\mathrm{Eu}$ has been observed by bombarding a $^{58}\mathrm{Ni}$ target with a beam of $425\phantom{\rule{0.3em}{0ex}}\text{MeV}$ $^{78}\mathrm{Kr}$ ions. Fusion evaporation residues were separated in-flight using the Argonne fragment mass analyzer and implanted into a double-sided silicon strip detector. $^{130}\mathrm{Eu}$ decays by the emission of a proton with energy ${E}_{p}=1020(15)\phantom{\rule{0.3em}{0ex}}\text{keV}\phantom{\rule{0.3em}{0ex}}[{Q}_{p}=1028(15)\phantom{\rule{0.3em}{0ex}}\text{keV}]$ and half-life ${t}_{1∕2}={0.90}_{\ensuremath{-}0.29}^{+0.49}\phantom{\rule{0.3em}{0ex}}\text{ms}$. The transition is assigned to a highly deformed $({\ensuremath{\beta}}_{2}\ensuremath{\sim}0.3){J}^{\ensuremath{\pi}}={1}^{+}$ ground-state configuration by comparing the decay rate with a new theoretical formalism for deformed odd-odd nuclei. These results clearly demonstrate the sensitivity of the proton decay rate to the spectator neutron configuration.

Proton decay in intersecting D-brane models

We analyze proton decay via dimension-six operators in certain GUT-like models derived from Type IIA orientifolds with D6-branes. The amplitude is parametrically enhanced by a factor of α GUT −1/3 relative to the corresponding result in four-dimensional GUTs. Nonetheless, even assuming a plausible enhancement from the threshold corrections, we find little overall enhancement of the proton decay rate from dimension-six operators, so that the predicted lifetime from this mechanism remains close to 10 36 years.

Proton decay in a consistent supersymmetric [formula omitted] GUT model

It is widely believed that minimal supersymmetric SU(5) GUTs have been excluded by the SuperKamiokande bound for the proton decay rate. However, in the minimal model, the theoretical prediction assumes unification of Yukawa couplings, Y d = Y e , which is known to be badly violated. We analyze the implications of this fact for the proton decay rate. In a consistent SU(5) model with higher dimensional operators, where SU(5) relations among Yukawa couplings hold, the proton decay rate can be several orders of magnitude smaller than the present experimental bound.

Neutrino mass, proton decay, and dark matter in TeV scale universal extra dimension models

We show how the problem of small neutrino masses and suppressed proton decay can be simultaneously resolved in 6-D universal extra dimension models (UED) with a low fundamental scale using extended gauge groups that contain the local $B-L$ symmetry. The extra space dimensions are compactified either on a $T^2/Z_2$ or $T^2/Z_2\times Z'_2$ orbifold depending on whether the full gauge group is $SU(2)_L\times U(1)_{I_{3R}}\times U(1)_{B-L}$ or $SU(2)_L\times SU(2)_{R}\times U(1)_{B-L}$. In both cases, neutrino masses are suppressed by an appropriate orbifold parity assignment for the standard model singlet neutrinos and the proton decay rate is suppressed due to a residual discrete symmetry left over from compactification. For lower values of the fundamental scale, a dominant decay mode of the neutron is $n\to 3 \nu$. An interesting consequence of the model is a possible two component picture for dark matter of the universe.

Dark matter andBs→μ+μ−with minimal SO10soft SUSY breaking

CMSSM boundary conditions are usually used when calculating cosmological dark matter densities. In this paper we calculate the cosmological density of dark matter in the MSSM using minimal $SO_{10}$ soft SUSY breaking boundary conditions. These boundary conditions incorporate several attractive features: they are consistent with $SO_{10}$ Yukawa unification, they result in a "natural" inverted scalar mass hierarchy and they reduce the dimension 5 operator contribution to the proton decay rate. With regards to dark matter, on the other hand, this is to a large extent an unexplored territory with large squark and slepton masses $m_{16}$, large $A_0$ and small $ \{\mu, M_{1/2} \} $. We find that in most regions of parameter space the cosmological density of dark matter is considerably less than required by the data. However there is a well--defined, narrow region of parameter space which provides the observed relic density of dark matter, as well as a good fit to precision electroweak data, including top, bottom and tau masses, and acceptable bounds on the branching fraction of $B_s \to \mu^+ \mu^-$. We present predictions for Higgs and SUSY spectra, the dark matter detection cross section and the branching ratio ${\rm BR}(B_s\to \mu^+ \mu^-)$ in this region of parameter space.

Unification in 5D SO(10)

Gauge unification in a five dimensional supersymmetric SO(10) model compactified on an orbifold $S^1/(Z_2 \times Z_2^{\prime})$ is studied. One orbifolding reduces N=2 supersymmetry to N=1, and the other breaks SO(10) to the Pati-Salam gauge group $\ps$. Further breaking to the standard model gauge group is made through the Higgs mechanism on one of the branes. The differences of the three gauge couplings run logarithmically even in five dimensions and we can keep the predictability for unification as in four dimensional gauge theories. We obtain an excellent prediction for gauge coupling unification with a cutoff scale $M_* \sim 3 \times 10^{17}$ GeV and a compactification scale $M_c \sim 1.5 \times 10^{14}$ GeV. Finally, although proton decay due to dimension 5 operators may be completely eliminated, the proton decay rate in these models is sensitive to the placement of matter multiplets in the 5th dimension, as well as to the unknown physics above the cutoff scale.

Proton decay due to bulk SU(5) gauge bosons in the Randall-Sundrum scenario

We calculate the proton decay rate due to five dimensional SU(5) gauge bosons in the Randall-Sundrum scenario with two branes (Planck brane and TeV brane). We consider matter in the usual 10 and \bar 5 SU(5) representations localized on a brane, and consider the case when SU(5) is broken by a Higgs mechanism on the matter brane. We calculate the proton decay rate mediated by X bosons, due to terms in the Lagrangian with X and its derivative along the extra dimension. We confirm that the experimental limit on the proton decay rate allows SU(5) matter to be on the Planck brane, but excludes it from being on the TeV brane in this scenario.

GUT breaking on the brane

We present a five-dimensional supersymmetric SU(5) theory in which the gauge symmetry is broken maximally (i.e., at the 5D Planck scale M ∗ ) on the same 4D brane where chiral matter is localized. Masses of the lightest Kaluza–Klein modes for the colored Higgs and X and Y gauge fields are determined by the compactification scale of the fifth dimension, M C ∼10 15 GeV, rather than by M ∗ . These fields' wave functions are repelled from the GUT-breaking brane, so that proton decay rates are suppressed below experimental limits. Above the compactification scale, the differences between the standard model gauge couplings evolve logarithmically, so that ordinary logarithmic gauge coupling unification is preserved. The maximal breaking of the grand unified group can also lead to other effects, such as O(1) deviations from SU(5) predictions of Yukawa couplings, even in models utilizing the Froggatt–Nielsen mechanism.

Proton stability and superstring Z′

Recently it was argued that proton lifetime limits impose that the scale of quantum gravity must be above 10 16 GeV. By studying the proton stability in the context of realistic heterotic-string models, I propose that proton longevity necessitates the existence of an additional U(1) Z′ symmetry, which is of non-GUT origin and remains unbroken down to intermediate, or low, energies. It is shown that the realistic string models frequently give rise to U(1) symmetries, which suppress the proton decay mediating operators, with, or without, the possibility of R-parity violation. By studying the F- and D-flat directions, I examine whether the required symmetries remain unbroken in the supersymmetric vacuum and show that in some examples they can, whereas in others they cannot. The proton decay rate is proportional to the U(1) Z′ symmetry breaking scale. Imposing the proton lifetime limits I estimate the U(1) Z′ breaking scale and show that if substantial R-parity violation is present the associated Z′ is within reach of forthcoming collider experiments.

Supersymmetric grand unification under siege: Proton lifetime upper bound

SO(10) supersymmetric (SUSY) grand unified theories provide a beautiful framework for physics beyond the standard model. Experimental measurements of the three gauge couplings are consistent with unification at a scale ${M}_{G}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{16}$ GeV. In addition, predictive models for fermion masses and mixing angles have been found which fit the low energy data, including the recent data for neutrino oscillations. SO(10) boundary conditions can be tested via the spectrum of superparticles. The simplest models also predict neutron and proton decay rates. In this paper we discuss nucleon decay rates and obtain reasonable upper bounds. A clear picture of the allowed SUSY spectra as constrained by nucleon decay is presented.

Proton, alpha and cluster decay rates for nuclei with [formula omitted] and [formula omitted

For studying the rates of radioactive nuclei in various decay chains we propose an approach unifying the advantages of the superfluid model for nucleon clustering and of the classical model for resonance tunneling in many-particle systems. We discuss the theoretical bases and numerical approach for decay rate predictions for some highly unstable proton rich trans-tin nuclei. Information on structure and nuclear mass of some exotic nuclei not yet experimentally accessible have also been obtained from a detailed analysis of the p, α and cluster decay rates. It is shown that the Casten-type rate systematics works very well in various schemes of valence nucleon numbers revealing similar decay properties for the nuclei with the same numbers of valence protons and neutrons above the 100 50Sn 50 and 208 82Pb 126 magic cores.

From minimal to realistic supersymmetric SU(5) grand unification

We construct and discuss a "realistic" example of SUSY SU(5) GUT model, with an additional U(1) flavour symmetry, that is not plagued by the need of large fine tunings, like those associated with doublet-triplet splitting in the minimal model, and that leads to an acceptable phenomenology. This includes coupling unification with a value of alpha_s(m_Z) in much better agreement with the data than in the minimal version, an acceptable hierarchical pattern for fermion masses and mixing angles, also including neutrino masses and mixings, and a proton decay rate compatible with present limits (but the discovery of proton decay should be within reach of the next generation of experiments). In the neutrino sector the preferred solution is one with nearly maximal mixing both for atmospheric and solar neutrinos.

The effect of lipid environment in purple membrane on bacteriorhodopsin

The decay rate of the Bacteriorhodopsin (BR) photocycle intermediate M 412 and proton, the proton pump efficiency (H +/M 412), the ratios of M 412 to other intermediates and the rotational correlation time ( τ c ) in purple membrane (PM) fragments treated by the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) with different concentrations were studied. The results show that: (1) The largest effect of CHAPS on M 412 decay rate and proton decay rate of BR, τ c of PM and the ratios of M 412 to other intermediates in BR photocycle is in the range of its critical micelle concentration (CMC). This indicates that changes of the ratios of M 412 to other intermediates, τ c , M 412 decay and proton decay occur and are due to the variation of the lipid environment. (2) The dependency of proton yield on CHAPS concentrations is basically consistent with that of M 412s%. This indicates the relation between proton pumping function and M 412. These studies show the importance of maintaining a native environment.

Exact calculation of proton decay rates from excited states in spherical nuclei

An exact approach for the determination of proton-decay widths in spherical nuclei is presented. It consists of solving numerically the one-dimensional time-dependent Schr\"odinger equation for initial proton quasistationary states obtained in the framework of a single-particle model. From the time dependence of the metastable state one can infer the dynamics of the decay and calculate the lifetime. The validity of this approach is demonstrated and quantitative comparisons with existing approximate, stationary methods are reviewed. Finally, the advantages and perspectives of this new method are discussed.

NON-SUSY AND SUSY ONE-STEP UNIFICATION

We explore the possibility of achieving one-step unification of the standard model coupling constants within non-supersymmetric and supersymmetric gauge models, which at low energies have only the standard particle content. The constraints are the experimental values of αem, αs and sin 2θW at 102 GeV, and the lower bounds for FCNC and proton decay rates. The analysis is done in a model-independent way.

Proton Radioactivity from Highly Deformed Nuclei

Proton radioactivity from ${}^{141}\mathrm{Ho}$ and ${}^{131}\mathrm{Eu}$ has been identified. The ${}^{141}\mathrm{Ho}$ proton transition has an energy ${E}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1169(8)\mathrm{keV}$, a half-life ${t}_{1/2}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.2(4)\mathrm{ms}$, and is assigned to the decay of the ${7/2}^{\ensuremath{-}}[523]$ Nilsson state. The ${}^{131}\mathrm{Eu}$ transition has an energy ${E}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}950(8)\mathrm{keV}$ and a half-life of 26(6) ms, consistent with decay from either the ${3/2}^{+}[411]$ or ${5/2}^{+}[413]$ Nilsson orbital. The proton decay rates deviate significantly from calculations assuming spherical configurations, and thus indicate the onset of large deformations in the region of the proton drip line below $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}69$.

Suggested new modes in supersymmetric proton decay

We show that in supersymmetric unified theories such as SO(10), implementation of the see–saw mechanism for neutrino masses introduces a new set of color triplet fields and thereby a new source of d=5 proton decay operators. For neutrino masses in a plausible range, these operators are found to have the right strength to yield observable, but not yet excluded, proton decay rates. The flavor structure of the new operators is distinctive. Proton decay modes into a charged lepton, such as ℓ + π 0, ℓ + K 0 and ℓ + η where ℓ= e or μ, can become prominent, even for low or moderate values of tan β≲10, along with the νK + and νπ + modes. A distinctive feature is the charged lepton modes involving an e + and/or a μ + with the ratio Γ(ℓ + K 0): Γ(ℓ + π 0)≃2:1.