قیل و قال علم

روزنوشت های علمی من

در آخر شهریور و اول مهر سال آینده همایش بین المللی دیگری روی موضوع فیزیک نوترینو ماده تاریک و فیزیک-بی در پژوهشکده فیزیک برگزار خواهیم کرد. فرم ثبت نام و اطلاعات بیشتر در این سایت قابل دسترس هست.

سال نو پیشاپیش مبارک باد!

+ نوشته شده در  چهارشنبه بیست و هفتم اسفند ۱۳۹۳ساعت 15:43  توسط یاسمن فرزان 

 

خواستم یادآوری کنم سال آینده من و شاهین دانشجو دکتری می گیریم. دقت کنید که نام پژوهشکده ما "پژوهشکده فیزیک" هست نه چیز دیگر. در انتخاب دقت لازم را مبذول نمایید.  در زیر اطلاعیه رسمی را می بینید:

 

 

پژوهشکده فیزیک در سال تحصیلی 95-94 از طریق آزمون سراسری ورودی دکتری در گرایش‌هایی که پژوهشکده در آن فعال است دانشجو می‌پذیرد. این گرایش‌ها عبارتند از فیزیک ذرات (پدیده‌شناسی و فیزیک انرژی‌های بالا- شاخه نظری)  و فیزیک محاسباتی (فیزیک ماده چگال، ماده نرم و آماری). اطلاعات مربوط به جزئیات سایر مراحل انتخاب و پذیرش دانشجو شامل امتحان و مصاحبه در پژوهشگاه پس از مرحله اول آزمون سراسری متعاقباً اعلام خواهد شد.  لازم به ذکر است متقاضیانی که مطابق ضوابط وزارتی مشمول استفاده از سهمیه استعدادهای درخشان می‌شوند، برای پذیرش باید در امتحان و مصاحبه ورودی پژوهشگاه نیز شرکت نمایند.

+ نوشته شده در  یکشنبه بیست و چهارم اسفند ۱۳۹۳ساعت 12:29  توسط یاسمن فرزان 

 Colloquium

 Colloquium  

Dear all,  It is an honor for me to announce that the speaker of the  next colloquium in Farvardin is Prof. Mehdi Zare of IIEES, Tehran. More information can be found in the textbox to the right.

Everybody is welcome to attend.

Happy new year for you and your family! With kind regards, Y. Farzan

 

Speaker

Prof. Mehdi Zare

Affliation

IIEES, Tehran پژوهشگاه بين المللي زلزله شناسي و مهندسي زلزله

Title of talk

An Overview on Earthquake Risk in Tehran Based on Recent Assessments نگاهي به ريسك زلزله در تهران

Date and time

19 Farvardin 1394 (8th April 2015), 4:30 pm

Place

Farmanieh Seminar Room

Abstract

 

 

The seismicity of the region of Tehran might be described on the reported  and recorded earthquakes during the history in this region. Very  recently, we could find some active trends in the region which their activity relate to eastern part of the region especially the North Tehran, Parchin,  Pishva, Mosha and the Garmsar faults. Also, we observed strong  historical earthquakes in this zone. Historical earthquakes showed that  the east of Tehran is more active than the west.  Released seismic  energy map of the region showed the main active zones with high energy  values for microearhquakes data in the east of the region.

The urbanization of Tehran is concentrated on the active fault zones  specially during the last 50 years; such that actually more that 3  million people are living in such dangerous active zones in the south  and north of Tehran. On the other hand, there is an assessment of 10.5  million people living in Tehran and Karaj and their suburbs (a total of  16.2 million population estimated to live in this region in January 2015)  in higher seismic vulnerable zones. We will keep in mind that there a  seismic gap along the major faults passing the urbanized areas of Tehran at least during the last 3000 years, which might be representative at  least for one major earthquake in the future (i.e. M6.5-M7.5). Such  major event might be a major threat for the security of the Capital of  the country. 

 

+ نوشته شده در  شنبه بیست و سوم اسفند ۱۳۹۳ساعت 15:32  توسط یاسمن فرزان 

arXiv:1503.02183 [pdf, other]
Oscillations of the $^7$Be solar neutrinos inside the Earth
Comments: 14 pages, 6 figures, LaTeX
Subjects: High Energy Physics - Phenomenology (hep-ph)

We explore in detail oscillations of the solar $^7$Be neutrinos in the matter of the Earth. The depth of oscillations is about $(0.1 - 0.2)\%$ and the length $\approx 30$ km. The period of the oscillatory modulations in the energy scale is comparable with the width of the line determined by the temperature in the center of the Sun. The latter means that depending on the length of trajectory (nadir angle) one obtains different degree of averaging of oscillations. Exploring these oscillations it is possible to measure the width of the $^7$Be line and therefore the temperature of the Sun, determine precisely $\Delta m^2_{21}$, perform tomography of the Earth, in particular, measure the deviation of its form from sphere, and detect small structures. Studies of the Be neutrinos open up a possibility to test quantum mechanics of neutrino oscillations and search for the sterile neutrinos. Accuracy of these measurements with future scintillator (or scintillator uploaded) detectors of the $\sim 100$ kton mass scale is estimated.

+ نوشته شده در  سه شنبه نوزدهم اسفند ۱۳۹۳ساعت 11:16  توسط یاسمن فرزان 

arXiv:1503.01773 [pdf, other]
Multi-Step Cascade Annihilations of Dark Matter and the Galactic Center Excess
Comments: 18 pages, 15 figures, 2 tables; comments welcome
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

If dark matter is embedded in a non-trivial dark sector, it may annihilate and decay to lighter dark-sector states which subsequently decay to the Standard Model. Such scenarios - with annihilation followed by cascading dark-sector decays - can explain the apparent excess GeV gamma-rays identified in the central Milky Way, while evading bounds from dark matter direct detection experiments. Each 'step' in the cascade will modify the observable signatures of dark matter annihilation and decay, shifting the resulting photons and other final state particles to lower energies and broadening their spectra. We explore, in a model-independent way, the effect of multi-step dark-sector cascades on the preferred regions of parameter space to explain the GeV excess. We find that the broadening effects of multi-step cascades can admit final states dominated by particles that would usually produce too sharply peaked photon spectra; in general, if the cascades are hierarchical (each particle decays to substantially lighter particles), the preferred mass range for the dark matter is in all cases 20-150 GeV. Decay chains that have nearly-degenerate steps, where the products are close to half the mass of the progenitor, can admit much higher DM masses. We map out the region of mass/cross-section parameter space where cascades (degenerate, hierarchical or a combination) can fit the signal, for a range of final states. In the current work, we study multi-step cascades in the context of explaining the GeV excess, but many aspects of our results are general and can be extended to other applications.

+ نوشته شده در  دوشنبه هجدهم اسفند ۱۳۹۳ساعت 11:43  توسط یاسمن فرزان 

arXiv:1503.00101 [pdf, ps, other]
How important is $iε$ in QFT?
Comments: 5 pages, 1 figure
Subjects: High Energy Physics - Phenomenology (hep-ph)

We discuss the role of $i\epsilon$ in quantum field theories and suggest that it can be identified with the dimensional regularization parameter $i\epsilon=4-d$ thus clarifying and simplifying issues related to the infrared divergences without altering any of the present knowledge in QFT. We further present the relevance of this assumption for the optical theorem.

 

منظورم از فلفل همون اپسیلن به ظاهر بی مصرف در مخرج انتشارگر هست. من هم نظریه میدان درس می دم می گم اونو دست کم نگیرید. کانتور که می بندید مهم می شه . نتیجه معجزه آسایش هم این می شه که از شر واگرایی و بی نهایت در تولید آن-شل ذرات ناپایدار در کانال اس رهایتان می کنه.

+ نوشته شده در  سه شنبه دوازدهم اسفند ۱۳۹۳ساعت 16:0  توسط یاسمن فرزان 

Colloquium

Physics Colloquium

 

Dear all, 
It is an honor for me to announce that the speaker of the colloquium this month is Prof. Sheikh-Jabbari. More information can be found in the textbox to the right. See also the attached file.



Everybody is welcome to attend.
With kind regards,
Y. Farzan

 

Speaker

Prof. M. M. Sheikh-Jabbari

Affliation

Physics school, IPM and Iranian academy of Sciences

Title of talk

Naturalness and Implications of LHC Results for Naturalness of Particle Physics Models

Date and time

20 Esfand 1393 (11th March 2015), 4:30 pm

Place

Farmanieh Seminar Room

Abstract

 

Naturalness of physical models which are based on the quantum field theory setups means that dimensionless parameters of the theory or dimensionful parameters measured in the energy scale of the model, are order one numbers; they are not very small or very large. Requirement of naturalness is not a direct outcome of the theoretical consistency of the physical models, nonetheless, it has been one of the important guiding principles in physical model building within quantum field theory settings. In this talk, I will first give some general remarks on the naturalness in established physical models. I will then focus on the case of particle physics standard model and in particular discuss implications of the LHC results, especially 126 GeV Higgs and the lower bound of about 800 GeV on SUSY particles, for the naturalness of standard model and supersymmetric models.

+ نوشته شده در  سه شنبه پنجم اسفند ۱۳۹۳ساعت 8:50  توسط یاسمن فرزان 

فایل صوتی سخنرانی من در روز چهارشنبه و اسلاید ها در  لینک های زیر در دسترس هست:

فایل صوتی

از زمان 1:40 به بعد فایل صوتی شاهین در مورد نظریه ریسمان صحبت می کند

اسلایدها

+ نوشته شده در  شنبه دوم اسفند ۱۳۹۳ساعت 14:17  توسط یاسمن فرزان 

Dear all,
. Instead, I will be happy to give a talk on neutrino physics this Wednesday. The talk will be at introductory level and comprehensible for non-experts

Everybody is welcome to attend. Undergraduate students are specially invited to do so.
With kind regards,
Y. Farzan

Speaker

Yasaman Farzan

Affliation

Physics school, IPM

Title of talk

Some established facts on neutrino physics
واقعیات پذیرفته شده در مورد فیزیک نوترینو

Date and Time

چهارشنبه, 29 بهمن 1393 ساعت چهار و نیم بعد از ظهر

(18th Februrary 2015), 4:30 pm

Place

Farmanieh Seminar Room

Abstract

I will briefly review the history of  neutrino physics taking shape and unraveling some of most important facts about these illusive particles that  has shaped 

our view on the realm of particle physics.

+ نوشته شده در  دوشنبه بیست و هفتم بهمن ۱۳۹۳ساعت 17:52  توسط یاسمن فرزان 

arXiv:1502.03821 (cross-list from astro-ph.GA) [pdf, other]
Evidence for dark matter in the inner Milky Way
Comments: First submitted version of letter published in Nature Physics on Febuary 9, 2015: this http URL
Journal-ref: Nature Physics 3237 (2015)
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Experiment (hep-ex); High Energy Physics - Phenomenology (hep-ph)

The ubiquitous presence of dark matter in the universe is today a central tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies to the observable universe, the evidence for dark matter is compelling in dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales. However, it has been historically difficult to pin down the dark matter contribution to the total mass density in the Milky Way, particularly in the innermost regions of the Galaxy and in the solar neighbourhood. Here we present an up-to-date compilation of Milky Way rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. We show that current data strongly disfavour baryons as the sole contribution to the galactic mass budget, even inside the solar circle. Our findings demonstrate the existence of dark matter in the inner Galaxy while making no assumptions on its distribution. We anticipate that this result will compel new model-independent constraints on the dark matter local density and profile, thus reducing uncertainties on direct and indirect dark matter searches, and will shed new light on the structure and evolution of the Galaxy.

+ نوشته شده در  دوشنبه بیست و هفتم بهمن ۱۳۹۳ساعت 10:17  توسط یاسمن فرزان 

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