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Nucleon decay in GUT and nonGUT SUSY models

Description: I first emphasize the importance of searching for nucleon decay in the context of supersymmetric models. The status of minimal SUSY SU(5) model is reviewed, which can be definitively ruled out by a combination of superKamiokande andLEP-2 experiments. Non-minimal models may provide some suppression in the nucleon decay rates, but there is still a good chance for superKamiokande. I point out that the operators suppressed even by the Planck-scale are too large. We need a suppression mechanism for the operators at the level of 10-7, and the mechanism, I argue, may well be a flavor symmetry. A particular example predicts p --> K0e+ to be the dominant mode which does not arise in GUT models.
Date: June 30, 1996
Creator: Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Alternatives to Seesaw

Description: The seesaw mechanism is attractive not only because it"explains'' small neutrino mass, but also because of its packaging with the SUSY-GUT, leptogenesis, Dark Matter, and electroweak symmetry breaking. However, this package has the flavor, CP, and gravitino problems. I discuss two alternatives to the seesaw mechanism. In one of them, the anomaly-mediated supersymmetry breaking solves these problems, while predicts naturally light Dirac neutrinos. In the other, the light Majorana neutrinos arise from supersymmetry breaking with right-handed neutrinos below TeV, and the Dark Matter and collider phenomenology are significantly different.
Date: October 10, 2004
Creator: Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Outlook: The Next Twenty Years

Description: I present an outlook for the next twenty years in particle physics. I start with the big questions in our field, broken down into four categories: horizontal, vertical, heaven, and hell. Then I discuss how we attack the bigquestions in each category during the next twenty years. I argue for a synergy between many different approaches taken in our field.
Date: December 7, 2003
Creator: Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

More visible effects of the hidden sector

Description: There is a growing appreciation that hidden sector dynamics may affect the supersymmetry breaking parameters in the visible sector (supersymmetric standard model), especially when the dynamics is strong and superconformal. We point out that there are effects that have not been previously discussed in the literature. For example, the gaugino masses are suppressed relative to the gravitino mass. We discuss their implications in the context of various mediation mechanisms. The issues discussed include anomaly mediation with singlets, the mu (B mu) problem in gauge and gaugino mediation, and distinct mass spectra for the superparticles that have not been previously considered.
Date: September 6, 2007
Creator: Murayama, Hitoshi; Murayama, Hitoshi; Nomura, Yasunori & Poland, David
Partner: UNT Libraries Government Documents Department

Neutrinoless Double Beta Decay in Light of SNO Salt Data

Description: In the SNO data from its salt run, probably the most significant result is the consistency with the previous results without assuming the 8B energy spectrum. In addition, they have excluded the maximal mixing at a very high confidence level. This has an important implication on the double beta decay experiments. For the inverted or degenerate mass spectrum, we find bar<m_nu>_ee bar> 0.013 eV at 95percent CL, and the next generation experiments can discriminate Majorana and Dirac neutrinos if the invertedor degenerate mass spectrum will be confirmed by the improvements in cosmology, tritium data beta decay, or long-baseline oscillation experiments.
Date: September 11, 2003
Creator: Murayama, Hitoshi & Pena-Garay, Carlos
Partner: UNT Libraries Government Documents Department

Gravitino Warm Dark Matter with Entropy Production

Description: Gravitinos with a mass in the keV range are an interesting candidate for warm dark matter. Recent measurements of the matter density of the universe and of cosmic structures at the dwarf galaxy scale rule out the simplest gravitino models with thermal freeze-out. We construct a model where the decay of the messenger particles that transmit the supersymmetry breaking to the observable sector generates the required entropy to dilute the gravitino relic density by the required factor of a few to come in line with observations. The model is natural, and requires only that the coupling of the messenger sector to the standard model be set so that the decay happens at the appropriate time.
Date: August 9, 2001
Creator: Baltz, Edward A. & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Non-universal SUSY breaking, hierarchy and squark degeneracty

Description: I discuss non-trivial effects in the soft SUSY breaking terms which appear when one integrates out heavy fields. The effects exist only when the SUSY breaking terms are non-universal. They may spoil (1) the hierarchy between the weak and high-energy scales, or (2) degeneracy among the squark masses even in the presense of a horizontal symmetry. I argue, in the end, that such new effects may be useful in probing physics at high-energy scales from TeV-scale experiments.
Date: March 15, 1995
Creator: Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department


Description: The author reviews phenomenologically interesting aspects of supersymmetry. First he points out that the discovery of the positron can be regarded as a historic analogue to the would-be discovery of supersymmetry. Second he reviews the recent topics on the unification of the gauge coupling constants, m{sub b}-M{sub {tau}} relation, proton decay, and baryogenesis. The author also briefly discusses the recent proposals to solve the problem of flavor changing neutral currents. Finally he argues that the measurements of supersymmetry parameters may probe the physics at the Planck scale.
Date: June 1, 1994
Creator: Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Proton hexality from an anomalous flavor U(1) and neutrino masses--Linking to the string scale

Description: We devise minimalistic gauged U(1)_X Froggatt-Nielsen models which at low-energy give rise to the recently suggested discrete gauge Z_6 symmetry, proton hexality, thus stabilizing the proton. Assuming three generations of right-handed neutrinos, with the proper choice of X-charges, we obtain viable neutrino masses. Furthermore, we find scenarios such that no X-charged hidden sector superfields are needed, which from a bottom-up perspective allows the calculation of g_string, g_X and G_SM's Kac-Moody levels. The only mass scale apart from M_grav is m_soft.
Date: August 7, 2007
Creator: Murayama, Hitoshi; Dreiner, Herbi K.; Luhn, Christoph; Murayama, Hitoshi & Thormeiere, Marc
Partner: UNT Libraries Government Documents Department

Matrix model description of baryonic deformations

Description: We investigate supersymmetric QCD with N{sub c} + 1 flavors using an extension of the recently proposed relation between gauge theories and matrix models.The impressive agreement between the two sides provides a beautiful confirmation of the extension of the gauge theory-matrix model relation to this case.
Date: March 13, 2003
Creator: Bena, Iosif; Murayama, Hitoshi; Roiban, Radu & Tatar, Radu
Partner: UNT Libraries Government Documents Department

How Can We Test Seesaw Experimentally?

Description: The seesaw mechanism for the small neutrino mass has been a popular paradigm, yet it has been believed that there is no way to test it experimentally. We present a conceivable outcome from future experiments that would convince us of the seesaw mechanism. It would involve a variety of data from LHC, ILC, cosmology, underground, and low-energy flavor violation experiments to establish the case.
Date: June 7, 2006
Creator: Buckley, Matthew R. & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Right-Handed New Physics Remains Strangely Beautiful

Description: Current data on CP violation in B_d -> eta' K_S and B_d -> phi K_S, taken literally, suggest new physics contributions in b -> s transitions. Despite a claim to the contrary, we point out that right-handed operators with a single weak phase can account for both deviations thanks to the two-fold ambiguity in the extraction of the weak phase from the corresponding CP-asymmetry. This observation is welcome since large mixing in the right-handed sector is favored by many GUT models and frameworks which address the flavor puzzle. There are also interesting correlations with the B_s system which provide a way to test this scenario in the near future.
Date: August 11, 2005
Creator: Larson, Daniel T.; Murayama, Hitoshi & Perez, Gilad
Partner: UNT Libraries Government Documents Department

Electroweak Symmetry Breaking via UV Insensitive Anomaly Mediation

Description: Anomaly mediation solves the supersymmetric flavor and CP problems. This is because the superconformal anomaly dictates that supersymmetry breaking is transmitted through nearly flavor-blind infrared physics that is highly predictive and UV insensitive. Slepton mass squareds, however, are predicted to be negative. This can be solved by adding D-terms for U(1)_Y and U(1)_{B-L} while retaining the UV insensitivity. In this paper we consider electroweak symmetry breaking via UV insensitive anomaly mediation in several models. For the MSSM we find a stable vacuum when tanbeta< 1, but in this region the top Yukawa coupling blows up only slightly above the supersymmetry breaking scale. For the NMSSM, we find a stable electroweak breaking vacuum but with a chargino that is too light. Replacing the cubic singlet term in the NMSSM superpotential with a term linear in the singlet wefind a stable vacuum and viable spectrum. Most of the parameter region with correct vacua requires a large superpotential coupling, precisely what is expected in the"Fat Higgs'" model in which the superpotential is generated dynamically. We have therefore found the first viable UV complete, UV insensitive supersymmetry breaking model that solves the flavor and CP problems automatically: the Fat Higgs model with UV insensitive anomaly mediation. Moreover, the cosmological gravitino problem is naturally solved, opening up the possibility of realistic thermal leptogenesis.
Date: February 19, 2004
Creator: Kitano, Ryuichiro; Kribs, Graham D. & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

What can we learn from neutrinoless double beta decay experiments?

Description: We assess how well next generation neutrinoless double beta decay and normal neutrino beta decay experiments can answer four fundamental questions. 1) If neutrinoless double beta decay searches do not detect a signal, and if the spectrum is known to be inverted hierarchy, can we conclude that neutrinos are Dirac particles? 2) If neutrinoless double beta decay searches are negative and a next generation ordinary beta decay experiment detects the neutrino mass scale, can we conclude that neutrinos are Dirac particles? 3) If neutrinoless double beta decay is observed with a large neutrino mass element, what is the total mass in neutrinos? 4) If neutrinoless double beta decay is observed but next generation beta decay searches for a neutrino mass only set a mass upper limit, can we establish whether the mass hierarchy is normal or inverted? We base our answers on the expected performance of next generation neutrinoless double beta decay experiments and on simulations of the accuracy of calculations of nuclear matrix elements.
Date: April 8, 2004
Creator: Bahcall, John N.; Murayama, Hitoshi & Pena-Garay, Carlos
Partner: UNT Libraries Government Documents Department

Dynamics of Supersymmetric SU(n_c) and USp(2n_c) Gauge Theories

Description: We study dynamical flavor symmetry breaking in the context of a class of N=1 supersymmetric SU(n_c) and USp(2 n_c) gauge theories, constructed from the exactly solvable N=2 theories by perturbing them with small adjoint and generic bare hypermultiplet (quark) masses. We find that the flavor U(n_f) symmetry in SU(n_c) theories is dynamically broken to $U(r)\times U(n_f-r)$ groups for $n_f \leq n_c$. In the r=1 case the dynamical symmetry breaking is caused by the condensation of monopoles in the $\underlinen_f$ representation. For general r, however, the monopoles in the $\underline_n_fC_r$ representation, whose condensation could explain the flavor symmetry breaking but would produce too-many Nambu--Goldstone multiplets, actually"break up'' into"magnetic quarks'' which condense and induce confinement and the symmetry breaking. In USp(2n_c) theories with $n_f\leq n_c + 1$, the flavor SO(2n_f) symmetry is dynamically broken to U(n_f), but with no description in terms of a weakly coupled local field theory. In both SU(n_c) and USp(2 n_c) theories, with larger numbers of quark flavors, besides the vacua with these properties, there exist also vacua with no flavor symmetry breaking.
Date: January 7, 2000
Creator: Carlino, Giuseppe; Konishi, Kenichi & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Anomalous Flavor U(1)_X for Everything

Description: We present an ambitious model of flavor, based on an anomalous U(1)_X gauge symmetry with one flavon, only two right-handed neutrinos and only two mass scales: M_{grav} and m_{3/2}. In particular, there are no new scales introduced for right-handed neutrino masses. The X-charges of the matter fields are such that R-parity is conserved exactly, higher-dimensional operators are sufficiently suppressed to guarantee a proton lifetime in agreement with experiment, and the phenomenology is viable for quarks, charged leptons, as well as neutrinos. In our model one of the three light neutrinos automatically is massless. The price we have to pay for this very successful model are highly fractional X-charges which can likely be improved with less restrictive phenomenological ansatze for mass matrices.
Date: December 1, 2003
Creator: Dreiner, Herbi K.; Murayama, Hitoshi & Thormeier, Marc
Partner: UNT Libraries Government Documents Department

Lepton-flavor mixing and K --> pi nu nu bar decays

Description: The impact of possible sources of lepton-flavor mixing on K {yields} {pi}{nu}{bar {nu}} decays is analyzed. At the one-loop level lepton-flavor mixing originated from non-diagonal lepton mass matrices cannot generate a CP-conserving K{sub L} {yields} {pi}{sup 0}{nu}{bar {nu}} amplitude. The rates of these modes are sensitive to leptonic flavor violation when there are at least two different leptonic mixing matrices. New interactions that violate both quark and lepton universalities could enhance the CP-conserving component of {Lambda}(K{sub L} {yields} {pi}{sup 0}{nu}{bar {nu}}) and have a substantial impact. Explicit examples of these effects in the context of supersymmetric models, with and without R-parity conservation, are discussed.
Date: November 26, 2003
Creator: Grossman, Yuval; Isidori, Gino & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

The New Minimal Standard Model

Description: We construct the New Minimal Standard Model that incorporates the new discoveries of physics beyond the Minimal Standard Model (MSM): Dark Energy, non-baryonic Dark Matter, neutrino masses, as well as baryon asymmetry and cosmic inflation, adopting the principle of minimal particle content and the most general renormalizable Lagrangian. We base the model purely on empirical facts rather than aesthetics. We need only six new degrees of freedom beyond the MSM. It is free from excessive flavor-changing effects, CP violation, too-rapid proton decay, problems with electroweak precision data, and unwanted cosmological relics. Any model of physics beyond the MSM should be measured against the phenomenological success of this model.
Date: January 13, 2005
Creator: Davoudiasl, Hooman; Kitano, Ryuichiro; Li, Tianjun & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Viable Supersymmetry and Leptogenesis with Anomaly Mediation

Description: The seesaw mechanism that explains the small neutrino masses comes naturally with supersymmetric (SUSY) grand unification and leptogenesis. However, the framework suffers from the SUSY flavor and CP problems, and has a severe cosmological gravitino problem. We propose anomaly mediation as a simple solution to all these problems, which is viable once supplemented by the D-terms for U(1)_Y and U(1)_B-L. Even though the right-handed neutrino mass explicitly breaks U(1)_B-L and hence reintroduces the flavor problem, we show that it lacks the logarithmic enhancement and poses no threat to the framework. The thermal leptogenesis is then made easily consistent with the gravitino constraint.
Date: January 13, 2005
Creator: Ibe, Masahiro; Kitano, Ryuichiro; Murayama, Hitoshi & Yanagida, Tsutomu
Partner: UNT Libraries Government Documents Department

A viable supersymmetric model with UV insensitive anomaly mediation

Description: We propose an electroweak model which is compatible with the UV insensitive anomaly mediated supersymmetry breaking. The model is an extension of the NMSSM by adding vector-like matter fields which can drive the soft scalar masses of the singlet Higgs field negative and the successful electroweak symmetry breaking is achieved. Viable parameter regions are found to preserve perturbativity of all the coupling constants up to the Planck scale. With this success, the model becomes a perfect candidate of physics beyond the standard model without the FCNC and CP problem. The cosmology is also quite interesting. The lightest neutralino is the wino which is a perfect cold dark matter candidate assuming the non-thermal production from the gravitino decay. There is no gravitino problem because it decays before the BBN era, and thus the thermal leptogenesis works. The cosmological domain wall problem inherent in the NMSSM is absent since the Z_3 symmetry is broken by the QCD instanton effect in the presence of the vector-like quarks. We also briefly comment on a possible solution to the strong CP problem a la the Nelson-Barr mechanism.
Date: December 14, 2004
Creator: Ibe, Masahiro; Kitano, Ryuichiro & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Light U(1) gauge boson coupled to baryon number

Description: The authors discuss the phenomenology of a light U(1) gauge boson, {gamma}{sub B}, that couples only to baryon number. Gauging baryon number at high energies can prevent dangerous baryon-number violating operators that may be generated by Planck scale physics. However, they assume at low energies that the new U(1) gauge symmetry is spontaneously broken and that the {gamma}{sub B} mass m{sub B} is smaller than m{sub z}. They show for m{sub {Upsilon}} < m{sub B} < m{sub z} that the {gamma}B coupling {alpha}{sub B} can be as large as {approximately} 0.1 without conflicting with the current experimental constraints. The authors argue that {alpha}{sub B} {approximately} 0.1 is large enough to produce visible collider signatures and that evidence for the {gamma}{sub B} could be hidden in existing LEP data. They show that there are realistic models in which mixing between the {gamma}{sub B} and the electroweak gauge bosons occurs only as a radiative effect and does not lead to conflict with precision electroweak measurements. Such mixing may nevertheless provide a leptonic signal for models of this type at an upgraded Tevatron.
Date: June 1, 1995
Creator: Carone, C.D. & Murayama, Hitoshi
Partner: UNT Libraries Government Documents Department

Probing Dark Energy via Neutrino and Supernova Observatories

Description: A novel method for extracting cosmological evolution parameters is proposed, using a probe other than light: future observations of the diffuse anti-neutrino flux emitted from core-collapse supernovae (SNe), combined with the SN rate extracted from future SN surveys. The relic SN neutrino differential flux can be extracted by using future neutrino detectors such as Gadolinium-enriched, megaton, water detectors or 100-kiloton detectors of liquid Argon or liquid scintillator. The core-collapse SN rate can be reconstructed from direct observation of SN explosions using future precision observatories. Our method, by itself, cannot compete with the accuracy of the optical-based measurements but may serve as an important consistency check as well as a source of complementary information. The proposal does not require construction of a dedicated experiment, but rather relies on future experiments proposed for other purposes.
Date: July 10, 2006
Creator: Hall, Lawrence; Hall, Lawrence J.; Murayama, Hitoshi; Papucci, Michele & Perez, Gilad
Partner: UNT Libraries Government Documents Department